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Brake bias, caliper BORE size and PAD recomendations... #1233067 05/14/12 02:11 AM 05/14/12 02:11 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Today my brother in law and I finished swapping a 904 into his Duster that was a 4 speed. On the spirited test drive, we ended up "testing" the brakes as well. Years back I swapped in a front disc setup from an 88 5th Avenue. The rear brakes are 10 inch drums. The brakes on this car would rival any new car. Non power master cylinder, but the pedal feel is great and this sucker just stops as if I threw out a grappling hook. What the heck? The brakes in the Charger have been a pisser. In February I added frame connectors and torque boxes. I had to reroute the front to rear brake line. The brakes were bled afterward, but they have given me trouble ever since. Since 2006, the system was: 12" Cordoba rotors, 75 Dart calipers in the front and the 10.7" rear disc brake kit from Dr Diff. I also used a power booster with a master cylinder from a 75 Dart. Braking was excellent except at low speeds since the idle vacuum was so low. I thought that switching to a NON power master cylinder would result in improved braking. It IS a little better, but after driving the BILs Duster, I have MUCH room for improvement. I've read in Mopar Action that the slider calipers have a tendency to allow the pads steel core to DIG into the sliding mechanism, causing the braking action to be radically compromised. I'm pulling the wheels tomorrow to get a look, but the point of this post is.... What relationship does the caliper bore size have to do with brake effectiveness? This Duster flat out STOPS better than any other A body that I've ever driven. It beats the Charger by a long shot. Its probably better that my 2007 Ram, and I've always been impressed with the truck. The only difference on the Duster is the calipers. I thought that I heard that the calipers on the 76 A bodies as well as the FMJ cars had different sized pistons. Does anyone know the specs on the different single piston calipers? I am tempted to swap in a pair of these later calipers if there are gains to be had. I really need the Charger to have brakes that equal the engine! Thanks, Greg. Last edited by Frankenduster; 05/14/12 04:34 AM.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233068 05/14/12 02:33 AM 05/14/12 02:33 AM
Joined: Jan 2006 Posts: 797 WA P pro451bee super stock
pro451bee super stock P Joined: Jan 2006 Posts: 797 WA	Factory Dart calipers do have a smaller piston ,so less pressure and could be a pad issue also.Try swaping your buddies brakes onto your knuckles for a test?

Re: Brake bias and caliper BORE size. [Re: pro451bee] #1233069 05/14/12 02:46 AM 05/14/12 02:46 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	THATs funny. He wouldn't object, but I dont want to jinx his car. It works, so I will let those sleeping dogs right where they are.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233070 05/14/12 04:34 AM 05/14/12 04:34 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Whenever I have doubts about interchange, I go to www.RockAuto.com. That site is great. I just look for part numbers that match and it really clears things up. Their site shows that the 73-75 A body cars used front calipers with 2.6" pistons. The 76 A body and ALL FMJ cars used calipers with 2.75" pistons. The Raybestos line showed those specs. Since the calipers and hoses can physically interchange, I'm inclined to just go ahead and get a pair of the 2.75 bore calipers.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233071 05/14/12 07:54 AM 05/14/12 07:54 AM
Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O 70Cuda383 Too Many Posts
70Cuda383 Too Many Posts Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O	well, a larger piston in the caliper gives you more clamping force for the same size master cylinder, so long as your master cylinder has enough stroke volume to operate the pistons without bottoming out. I just put big brakes on my dakota, went from 10" drum brakes in the rear to 4-piston Brembo calipers on a 13" rotor. on the stock master cylinder, my pedal would go to the floor without generating any real braking effort, and I had to step up to a larger diameter master to get enough stroke volume for the big rear brakes. I think I read on one of Andy's posts that it's not about pad size, but rather, it's all about caliper clamping force. the size of the pad only determines how fast the pad wears. Photobucket sucks

Re: Brake bias and caliper BORE size. [Re: 70Cuda383] #1233072 05/14/12 09:03 PM 05/14/12 09:03 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Heres a few more tidbits: I pulled the wheels to get a look at the calipers. The channel in the caliper mount that the caliper and inner pad ride upon had a few indentations. I read about this in Mopar Action. Rick wrote that this area is problematic, and that a recess here could cause the pads to hang up. I took a flat file and milled down the area until it was smoothe. The pads move free now. I drove the car and noticed no improvement. On the way home, I stood on the brakes harder than ever. It finally locked the REAR wheels. I haven't been able to get a tire to skid in months. Now with the rear skidding, it appears that I need the bias to shift towards the front. The larger piston calipers should help, right? Oddly, the car also stops BETTER in reverse than going forward. I don't understand THAT at all. I bought 2 Raybestos 2.75 calipers and new pads. I'll get them on tomorrow and report back.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233073 05/15/12 02:09 AM 05/15/12 02:09 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Does anyone have a suggestion for caliper piston bias for 4 wheel disc applications? Like many people here, my cars are a sort of "Mr Potato Head" creations. Lots of parts from different cars. A stock bias may not be right for a lowered car with a cornering suspension. There isn't the same degree of brake dive with the stiffer suspension, so in theory, the rear brakes are less likely to skid due to rear end rise. The stock setup for a 75 A body disc/drum car is as follows: 2.60" caliper pistons and 15/16" drum wheel cylinders. This is also with 1" bore NON power master cylinder. MY car has 2.60 front calipers and what appears to be 1 7/16" rear calipers. (Dr Diff Cobra brake kit) It worked great with the power setup except at low speeds/low vacuum.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233074 05/15/12 09:27 AM 05/15/12 09:27 AM
Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O 70Cuda383 Too Many Posts
70Cuda383 Too Many Posts Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O	I always thought you wanted 1000-1200 psi at the caliper for a disc brake system. as far as front/rear bias, if you can't get it dialed in perfectly with just piston sizes, I would err on the side of caution, and go bigger on the rear, then use an adjustable proportioning valve to dial it back so they lock up evenly. you NEVER want to put any kind of prop valve or pressure limiting valve on the fronts! Also, car suspension can greatly effect brake bias. if you have a soft or worn out suspension, all your weight will shift forward, the nose will dive down, and the rear end will get very light. this will cause the rear to lock up before the fronts as well, even if the brake system is evenly matched. Photobucket sucks

Re: Brake bias and caliper BORE size. [Re: 70Cuda383] #1233075 05/15/12 10:03 AM 05/15/12 10:03 AM
Joined: Sep 2007 Posts: 14,889 up yours Supercuda About to go away
Supercuda About to go away Joined: Sep 2007 Posts: 14,889 up yours	No too sure your disc/drum master cylinder is the best choice for an all disc system. Lack of volume for the rear calipers. Also, if you flipped the spindles for sway bar clearance make triply sure the bleeder valve is at the high point of the caliper bore, otherwise you will trap some air and you will have lousy brakes. They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.

Re: Brake bias and caliper BORE size. [Re: Supercuda] #1233076 05/15/12 10:09 AM 05/15/12 10:09 AM
Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O 70Cuda383 Too Many Posts
70Cuda383 Too Many Posts Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O	Quote: No too sure your disc/drum master cylinder is the best choice for an all disc system. Lack of volume for the rear calipers. Also, if you flipped the spindles for sway bar clearance make triply sure the bleeder valve is at the high point of the caliper bore, otherwise you will trap some air and you will have lousy brakes. I thought I read somewhere in one of his threads that he has an aftermarket, disc/disc master with a 15/16" bore? Photobucket sucks

Re: Brake bias and caliper BORE size. [Re: 70Cuda383] #1233077 05/15/12 10:21 AM 05/15/12 10:21 AM
Joined: Sep 2007 Posts: 14,889 up yours Supercuda About to go away
Supercuda About to go away Joined: Sep 2007 Posts: 14,889 up yours	went baack an reread this thread, only mc he mentioned is from a 75 Dart, dunno what he has in it for sure They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.

Re: Brake bias and caliper BORE size. [Re: Supercuda] #1233078 05/15/12 10:49 AM 05/15/12 10:49 AM
Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O 70Cuda383 Too Many Posts
70Cuda383 Too Many Posts Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O	Quote: went baack an reread this thread, only mc he mentioned is from a 75 Dart, dunno what he has in it for sure yea, he said it in his other thread, I went back to verify that I did infact read it in his thread...so many brake threads on here right now! this one he posted in the Q&A forum... https://board.moparts.org/ubbthreads/show...e=0#Post7206072 Photobucket sucks

Re: Brake bias and caliper BORE size. DELETED [Re: Kern Dog] #1233079 05/15/12 11:21 AM 05/15/12 11:21 AM
Joined: May 2005 Posts: 416 Franklin Co. Illinois runinonmt mopar
runinonmt mopar Joined: May 2005 Posts: 416 Franklin Co. Illinois	Post deleted by runinonmt In sixty-five I was seventeen and running up one-o-one I don't know where I'm running now, I'm just running on Jackson Browne-Running On Empty

Re: Brake bias and caliper BORE size. [Re: runinonmt] #1233080 05/15/12 01:02 PM 05/15/12 01:02 PM
Joined: Sep 2007 Posts: 14,889 up yours Supercuda About to go away
Supercuda About to go away Joined: Sep 2007 Posts: 14,889 up yours	he's got 4 wheel discs They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.

Re: Brake bias and caliper BORE size. [Re: Supercuda] #1233081 05/15/12 03:06 PM 05/15/12 03:06 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	I've been pretty confused with these brakes, I forgot to mention in this post that I currently have an aluminum 15/16" 4 wheel disc master cylinder on the car. It stopped BETTER with the power booster and a factory 75 Dart disc/drum master!

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233082 05/15/12 03:31 PM 05/15/12 03:31 PM
Joined: Sep 2007 Posts: 14,889 up yours Supercuda About to go away
Supercuda About to go away Joined: Sep 2007 Posts: 14,889 up yours	The power brake m/c for a 75 Dart looks to be 15/16". the manual one is 1 1/32". Either your new m/c is flaky or you need to upsize it. They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.

Re: Brake bias and caliper BORE size. [Re: Supercuda] #1233083 05/15/12 04:16 PM 05/15/12 04:16 PM
Joined: Jan 2003 Posts: 8,016 Polson, MT DoctorDiff master
DoctorDiff master Joined: Jan 2003 Posts: 8,016 Polson, MT	Sounds like he had an iron 15/16" bore master with power brakes. He now has an aluminum 15/16" bore master with manual brakes. All else being equal, a larger bore master cylinder will DECREASE line pressure at the calipers. Contact info

Re: Brake bias and caliper BORE size. [Re: Supercuda] #1233084 05/15/12 06:48 PM 05/15/12 06:48 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Quote: The power brake m/c for a 75 Dart looks to be 15/16". the manual one is 1 1/32". Either your new m/c is flaky or you need to upsize it. I bought the aluminum master cylinder from Dr Diff. He has the best rep in the business, so I trust his judgement. Regarding the bore diameter of the stock stuff, it appears to me that you may have your spec's backwards. Wouldn't it make more sense for the power applications to use a LARGER bore since they have assistance to push it? Just an idea. I haven't measured the iron power M/C yet.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233085 05/15/12 06:50 PM 05/15/12 06:50 PM
Joined: Sep 2007 Posts: 14,889 up yours Supercuda About to go away
Supercuda About to go away Joined: Sep 2007 Posts: 14,889 up yours	I looked them up at Rock Auto, assuming they had it right I simply posted what they spec'd. They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233086 05/15/12 08:41 PM 05/15/12 08:41 PM
Joined: Jan 2003 Posts: 8,016 Polson, MT DoctorDiff master
DoctorDiff master Joined: Jan 2003 Posts: 8,016 Polson, MT	'73-'75 power brake equipped A-bodies used (smaller) 15/16" bore master cylinders because the booster linkage yields a mechanical disadvantage. Contact info

Re: Brake bias and caliper BORE size. [Re: DoctorDiff] #1233087 05/15/12 10:33 PM 05/15/12 10:33 PM
Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O 70Cuda383 Too Many Posts
70Cuda383 Too Many Posts Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O	Quote: '73-'75 power brake equipped A-bodies used (smaller) 15/16" bore master cylinders because the booster linkage yields a mechanical disadvantage. and the other half of that equation...do those cars use larger wheel cylinders? Photobucket sucks

Re: Brake bias and caliper BORE size. [Re: DoctorDiff] #1233088 05/16/12 12:51 AM 05/16/12 12:51 AM
Joined: Jan 2003 Posts: 28,067 Irving, TX feets Senior Management
feets Senior Management Joined: Jan 2003 Posts: 28,067 Irving, TX	Quote: '73-'75 power brake equipped A-bodies used (smaller) 15/16" bore master cylinders because the booster linkage yields a mechanical disadvantage. 5:1 pedal ratio for manual brake cars. 4:1 pedal ratio for power brake cars. I think that's right. If not, the info was worth what you paid for it. We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon

Re: Brake bias and caliper BORE size. [Re: 70Cuda383] #1233089 05/16/12 01:08 AM 05/16/12 01:08 AM
Joined: Jan 2003 Posts: 8,016 Polson, MT DoctorDiff master
DoctorDiff master Joined: Jan 2003 Posts: 8,016 Polson, MT	As far as I know, '73-'75 A-bodies use (small) 2.6" bore front calipers and (standard) 15/16" bore rear wheel cylinders. On paper, this sounds very rear biased. This may be the reason A-bodies went to standard 2.75" bore calipers in '76. Contact info

Re: Brake bias and caliper BORE size. [Re: DoctorDiff] #1233090 05/16/12 01:59 AM 05/16/12 01:59 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	I installed the 2.75 calipers today along with new semi metallic pads. The brakes are still terrible. EVERY move that I have made with a manual brake master cylinder has resulted in poor results. The 15/16" aluminum master is the only one though that will actually stop the car. Sadly, that just isn't enough. I want brakes that have the ability to skid! As I remember, the brakes are working their hardest just before they lock up. I shouldn't have to stand on the pedal to get there. I've tried both disc/drum and drum/drum combo valves with no noticeable difference. I get fluid movement when I crack the bleeders. I guess it would be interesting to know what the pressure should be at the calipers, so I could buy a guage and test it. Regardless, I'm leaning toward a return to the power brake setup that I had before. When I posted about it some time ago, I had a few responses that suggested adding a vacuum pump to the existing power brakes. I shunned the idea because others chimed in about how their manual brake cars stopped great. Obviously there is a fatal flaw to my system, because so far, it defies logical understanding.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233091 05/16/12 02:28 AM 05/16/12 02:28 AM
Joined: Jan 2003 Posts: 28,067 Irving, TX feets Senior Management
feets Senior Management Joined: Jan 2003 Posts: 28,067 Irving, TX	If you're running a power pedal with a manual master you're losing pressure. Either find a manual brake pedal or move the brake push rod higher on the pedal. Measure from the center of the brake pedal pivot to the middle of the brake pedal pad. Measure from the center of the brake pedal pivot to the center of the pin where master cylinder push rod connects to the pedal. It's needs to be a 5:1 ratio for factory sized master cylinders to work. If you have a power pedal the leverage is greatly reduced. A "correct" sized master cylinder will require a lot more leg effort to get the same brake pressure. To calculate line pressure do the math. (input force * pedal ratio) / surface area of master cylinder piston Here's a list of master cylinder sizes and line pressures using a 4:1 pedal ratio and a 150 lbs pedal force: 3/4" = 1364 psi 7/8" = 1000 psi 15/16" = 869 psi 1" = 759 psi 1-1/8" = 606 psi 1-1/4" = 488 psi Now, using a 5:1 pedal ratio and 150 lbs pedal force you get: 3/4" = 1705 psi 7/8" = 1250 psi 15/16" = 1086 psi 1" = 949 psi 1-1/8" = 758 psi 1-1/4" = 610 psi Does that help? Your 15/16" master cylinder with a 4:1 ratio and pedal effort of 172 lbs gives you 1000 psi. Assume you weigh 172 lbs. Stand on one leg. Do a deep knee bend. The amount of force needed to stand up straight again with one leg is how hard you have to push on the pedal to get the pressure listed above. You want a minimum of 1000 psi working pressure. To get 1200 psi for a comfortable margin you have to push with 207 lbs of force. Either fix the pedal or find a 3/4" master cylinder and hope it has enough travel to make up for the pistons moving. We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon

Re: Brake bias and caliper BORE size. [Re: feets] #1233092 05/16/12 04:08 AM 05/16/12 04:08 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Feets, I'm impressed and honored. That post took some effort and I thank you. This car started out with manual 4 wheel drums. I converted it to Power front disc/rear drum, then to Power 4 wheel disc. Now it is a non power 4 wheel disc. It has the same brake pedal that was in the car when I bought it. I'll have to check and calc the pedal ratio, then report back. I seem to remember that some cars had 2 holes in the brake pedal lever, the top one was supposed to be for manual brakes. I don't recall seeing any 67-76 A bodies that were like this and my Charger certainly isnt. On another note I had the idea of eliminating the combination block, thinking that there may be a better way. I was thinking of running the M/C rearmost port to a TEE which will split off to each front wheel, then run the forewardmost M/C line to the rear with an adjustable proportioning valve in line. My thinking is that THIS may be a "work around" to a possibly defective combo valve. I posted this question elsewhere and a few suggested simply gutting the combo valve and keeping it. I took a drum/drum and a disc/drum combo valve and took the parts out. I blew compressed air through both and found that even with the guts removed, the front and rear ports remained seperate! The combo valve mods are moot if my pedal ratio is waaay off. Another thought: Since the car WAS 4 wheel drum, and since drums require LESS volume to operate, maybe the existing pedal ratio is simply not compatible with a 4 disc system.

Re: Brake bias and caliper BORE size. [Re: feets] #1233093 05/16/12 04:35 AM 05/16/12 04:35 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Quote: 5:1 pedal ratio for manual brake cars. 4:1 pedal ratio for power brake cars. I think that's right. If not, the info was worth what you paid for it. Okay, I'm back. Using the instructions given, my pedal ratio is quite different. I measured from the center of the brake pedal pad to the center of the point at which it swings...12 3/8" The measurement from the pivot to the center of the brake pushrod bolt is 1 7/8". This works out to a 6.6 ratio. I had a mid 70s A body pedal assembly nearby and looked at it for comparison. I got 11 1/4" and 1 5/8" for a ratio of 6.92. I measured AND did the math twice. For the Charger, the brake pushrod would've needed to be 3 1/32" away to be at a 4 to 1 ratio or 2 1/2" away to be close to the 5 to 1 number. It was worth a try.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233094 05/16/12 09:23 AM 05/16/12 09:23 AM
Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O 70Cuda383 Too Many Posts
70Cuda383 Too Many Posts Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O	Quote: Quote: 5:1 pedal ratio for manual brake cars. 4:1 pedal ratio for power brake cars. I think that's right. If not, the info was worth what you paid for it. Okay, I'm back. Using the instructions given, my pedal ratio is quite different. I measured from the center of the brake pedal pad to the center of the point at which it swings...12 3/8" The measurement from the pivot to the center of the brake pushrod bolt is 1 7/8". This works out to a 6.6 ratio. I had a mid 70s A body pedal assembly nearby and looked at it for comparison. I got 11 1/4" and 1 5/8" for a ratio of 6.92. I measured AND did the math twice. For the Charger, the brake pushrod would've needed to be 3 1/32" away to be at a 4 to 1 ratio or 2 1/2" away to be close to the 5 to 1 number. It was worth a try. So you're getting MORE leverage then, if it's 6.6 ratio. maybe you need to go hit the gym? I'd try dropping to the 3/4" master. Photobucket sucks

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233095 05/16/12 10:10 AM 05/16/12 10:10 AM
Joined: Jan 2003 Posts: 8,016 Polson, MT DoctorDiff master
DoctorDiff master Joined: Jan 2003 Posts: 8,016 Polson, MT	Only pre '66 B-bodies used a different pedal for power brakes. I have a few 7/8" bore master cylinders, but that seems kind of extreme. You probably don't need any rear proportioning with your particular disc/disc combination. Did you try a simple drum brake distribution valve? Can you get more aggressive front brake pads? Contact info

Re: Brake bias and caliper BORE size. [Re: Supercuda] #1233096 05/16/12 10:49 AM 05/16/12 10:49 AM
Joined: May 2005 Posts: 416 Franklin Co. Illinois runinonmt mopar
runinonmt mopar Joined: May 2005 Posts: 416 Franklin Co. Illinois	Quote: he's got 4 wheel discs Oops.Silly me. In sixty-five I was seventeen and running up one-o-one I don't know where I'm running now, I'm just running on Jackson Browne-Running On Empty

Re: Brake bias and caliper BORE size. [Re: runinonmt] #1233097 05/16/12 02:20 PM 05/16/12 02:20 PM
Joined: Jul 2010 Posts: 184 Vernon Ct. B bp27 member
bp27 member B Joined: Jul 2010 Posts: 184 Vernon Ct.	This mite be a long shot but how are your flex hoses? when thay go bad thay can make the peddel feel spunge.

Re: Brake bias and caliper BORE size. [Re: runinonmt] #1233098 05/16/12 02:28 PM 05/16/12 02:28 PM
Joined: Feb 2011 Posts: 4,302 Nebraska 72Swinger master
72Swinger master Joined: Feb 2011 Posts: 4,302 Nebraska	I have 74 Dart front calipers,Dr Diff 15/16" MC,11" rear drums and a factory original to my car Drum/drum prop valve and my car stops as good as anything i've ever driven with no rear lockup. My pedal and rod are also orignal manual stuff. If you want I can measure my pedal ratio. It sounds to me like my setup is identical to yours other than the rear discs. Mopar to the bone!!!

Re: Brake bias and caliper BORE size. [Re: DoctorDiff] #1233099 05/16/12 02:52 PM 05/16/12 02:52 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Quote: Only pre '66 B-bodies used a different pedal for power brakes. I have a few 7/8" bore master cylinders, but that seems kind of extreme. You probably don't need any rear proportioning with your particular disc/disc combination. Did you try a simple drum brake distribution valve? Can you get more aggressive front brake pads? I have tried 2 different combination valves, a 75 Dart disc/drum and a drum/drum. The drum/drum valve is in place now. Both delivered the same feel. I may have not mentioned it, but it sorta feels as if the front end isn't getting enough line pressure. On other factory based master cylinders, the outlet fittings are different sizes to ensure the proper front/rear placement. THIS 15/16" master has similar ports front and rear. I have the rearmost reservior connected to the front brakes like a factory application. MORE aggressive front pads? That is an idea. I also have been asked if the current new pads have been bedded in yet. Simply put, if the braking im proved by 20%, they would still suck. It really is that bad. What are the chances of having TWO combo valves with internal blockages? I have considered plumbing the lines without a factory valve.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233100 05/16/12 02:56 PM 05/16/12 02:56 PM
Joined: Oct 2007 Posts: 3,871 Oregon hooziewhatsit master
hooziewhatsit master Joined: Oct 2007 Posts: 3,871 Oregon	Quote: Feets, I'm impressed and honored. That post took some effort and I thank you. Subscribing so I can find this thread again later when I look at my brake issues again. Quote: Can you get more aggressive front brake pads? Is there a certain type that's more aggressive than others? I'm running Autozone cheapies () in my truck, and they just don't seem to have any 'bite'. If you ever find yourself in a fair fight, your tactics suck.

Re: Brake bias and caliper BORE size. [Re: Supercuda] #1233101 05/16/12 08:33 PM 05/16/12 08:33 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Quote: The power brake m/c for a 75 Dart looks to be 15/16". the manual one is 1 1/32". Either your new m/c is flaky or you need to upsize it. I owe you an apology! I just removed the M/C from the power booster that I previously had on the car. The bore WAS 15/16". To confirm, I pulled the M/C from a 73 Dart power disc car. It too was 15/16". I checked my NON power A body factory disc master and it looked like 1 1/16" but it could have been 1 1/32"... hard to tell when they are that close. This is odd. Maybe the increased pedal ratio of the manual setup overcomes the bigger bore?

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233102 05/16/12 11:05 PM 05/16/12 11:05 PM
Joined: Sep 2007 Posts: 14,889 up yours Supercuda About to go away
Supercuda About to go away Joined: Sep 2007 Posts: 14,889 up yours	Well, I am just a piece of carp anyway, lol. I am running manual brakes on my 65 Cuda, 11.75" disc/11" drums. Running the M/C out of a late M body, forget the diameter offhand, but the pedal is not as firm as I would like. I think it's a bleeder on the caliper location issue but haven't gotten around to verifying it yet. I forget, it's been years, exactly what caliper I am running, I think M body and I flipped the calipers to clear the swaybar. This might have put the bleeders in less than optimal position causing my issue. Are you 100% sure the bleeders are at the very top of the caliper bore? They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.

Re: Brake bias and caliper BORE size. [Re: Supercuda] #1233103 05/17/12 12:34 AM 05/17/12 12:34 AM
Joined: Jan 2003 Posts: 28,067 Irving, TX feets Senior Management
feets Senior Management Joined: Jan 2003 Posts: 28,067 Irving, TX	The hot rod has 8 piston calipers up front. The total working area is 4.40 square inches. The rear 4 piston calipers have a working area of 2.05 square inches. I use a 1-1/8" master cylinder on the stock manual brake pedal. I don't remember the pedal ratio. This setup have the best feeling manual brakes I've ever driven. The pedal isn't hard to push and the car slows down as soon as the pedal moves. It's a beautiful thing. Despite soft 245/45-18 and 295/45-18 tires I can lock the brakes without excessive pedal pressure. My situation is a little different with 14.25" front rotors and 13" rear rotors. Your front calipers have a piston area of 5.94 square inches and the rears are 2.43 square inches. Both calipers displace more fluid than mine. Your rotors are 11.75" front and 10.7" rear. I would have to sit down and calculate the difference in brake force between my setup and yours assuming we have the same pedal ratio. I might have to step out into the shop and measure my pedal. We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon

Re: Brake bias and caliper BORE size. [Re: feets] #1233104 05/17/12 01:10 AM 05/17/12 01:10 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Quote: 8 piston calipers up front. The total working area is 4.40 square inches. The rear working area is 2.05 square inches. This makes the rear caliper force about 46 % of the front. Your front calipers have a piston area of 5.94 square inches and the rears are 2.43 square inches. Both calipers displace more fluid than mine. Your rotors are 11.75" front and 10.7" rear. Using the same math, my numbers show the rear calipers here have 41 % of the front I guess this means that I would have a little less rear bias, which I call a GOOD thing!

Re: Brake bias and caliper BORE size. [Re: feets] #1233105 05/17/12 10:06 AM 05/17/12 10:06 AM
Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O 70Cuda383 Too Many Posts
70Cuda383 Too Many Posts Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O	Quote: The hot rod has 8 piston calipers up front. The total working area is 4.40 square inches. The rear 4 piston calipers have a working area of 2.05 square inches. I use a 1-1/8" master cylinder on the stock manual brake pedal. I don't remember the pedal ratio. This setup have the best feeling manual brakes I've ever driven. The pedal isn't hard to push and the car slows down as soon as the pedal moves. It's a beautiful thing. Despite soft 245/45-18 and 295/45-18 tires I can lock the brakes without excessive pedal pressure. My situation is a little different with 14.25" front rotors and 13" rear rotors. That's not bad at all! for comparison, the Gen 2 viper calipers have a combined surface area of 3.88 square inches, and used a 1 1/16" master cylinder with a power booster. I'm running those calipers with a 1 1/8" master on my power brake booster on the Dakota. I love how they borrow parts from each other too! the 03/04 dakota master cylinder is exactly the same as the gen III Viper master cylinders, and the 97-02 Dakota master, the 92-02 Viper master, 03-12 Viper master, and 03/04 Dakota master, all have the same piston depth into the brake booster, the same bolt pattern to bolt the master to the booster, and thus, all 4 masters are interchangable! (with the exception that the gen 2 viper masters use SAE double flare fittings, and the other 3 use metric bubble flare fittings) with my brakes on the booster, it feels really good. If I was to manual brakes, I'd probably find a disc/disc master that was 1 1/16" with these viper calipers. Photobucket sucks

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233106 05/17/12 12:44 PM 05/17/12 12:44 PM
Joined: Jan 2003 Posts: 28,067 Irving, TX feets Senior Management
feets Senior Management Joined: Jan 2003 Posts: 28,067 Irving, TX	I crashed some numbers around last night but lost my internet connection and couldn't post 'em. I compared the hot rod to your car. This wasn't an attempt to make my car look good. The hot rod's brakes work well and I could find all the numbers involved. The pedal ratio on the hot rod is 7.125:1 so my guess was WAY off. I looked at the pedal ratio, MC bore size, and effective brake radius of the cars. With the hot rod, 100 lb pedal effort makes 4883 lb/ft of front brake torque. With your car 100 lb pedal effort makes 4961 lb/ft of front brake torque. The 1.5% will never be seen in the real world. Comparing master cylinder volume to brake caliper volume will show some interesting numbers. When my master moves 1 inch the front calipers move out .1129". When your master cylinder moves 1 inch the calipers move .058". The resulting pedal feel will be quite different. Brake pads are usually a few thousandths of an inch off the rotors unless the rotor is not round. If you have pad material built up on the rotor or lots of runout the pads will get knocked back away from the rotor. Shifting to the rear.. The hot rod turns 100 lb pedal effort into 2156 lb/ft of brake torque. Your car turns 100 lb pedal effort into 1355 lb/ft of brake torque. The 38% difference will be very noticeable. When my master cylinder moves 1" the rear caliper pistons move .242". When your master cylinder moves 1" the rear caliper pistons move .142". *EDIT* I butchered some of those numbers. oopsie. The comparisons between the two systems are the same so you can still learn what you needed to learn. See this post for more accurate info. We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon

Brake bias and caliper BORE size. More clues inside! [Re: feets] #1233107 05/17/12 02:38 PM 05/17/12 02:38 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Quote: I crashed some numbers around last night but lost my internet connection and couldn't post 'em. Comparing master cylinder volume to brake caliper volume will show some interesting numbers. When my master moves 1 inch the front calipers move out .1129". When your master cylinder moves 1 inch the calipers move .058". W O W !! Is this because of the small bore master cylinder moves LESS volume or is it a combination of master cylinder AND pedal ratio? NOT doubting you, I just wondered about the math involved. Last edited by Frankenduster; 05/19/12 02:25 AM.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233108 05/17/12 04:58 PM 05/17/12 04:58 PM
Joined: Jan 2003 Posts: 28,067 Irving, TX feets Senior Management
feets Senior Management Joined: Jan 2003 Posts: 28,067 Irving, TX	The piston movement is easy to figure. You look at the bore of the master cylinder and the bore of the caliper pistons. Divide the master cylinder bore by the caliper piston bore. Take that total and divide by two since you have calipers on the left and right. Figuring one inch of movement is easy. Multiply the area by 1. Can't get much easier than that. At one inches of depth your master cylinder holds .6901 cubic inches of fluid. The calipers have 5.94 square inches of surface area. You have two of them for a total of 11.88 square inches. Take a pan with an area of 11.88 square inches and drop in .69 cubic inches of water. How deep do you think it's going to be? We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon

Re: Brake bias and caliper BORE size. [Re: feets] #1233109 05/17/12 05:33 PM 05/17/12 05:33 PM
Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O 70Cuda383 Too Many Posts
70Cuda383 Too Many Posts Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O	yup. When calculating pressure or force generated at the caliper, that's a 2 dimensional calculation. area of master cylinder vs area of caliper pistons. when calculating pad movement, that's a 3 dimensional calculation, master cylinder piston area times height (or stroke) vs caliper piston area times height/stroke. as an example, I just had a rotor that was .030 out of round. that means as it rotated, it would push the pad and pistons back into the caliper. .030 of movement ends up being .060 of total displacement, because both the outter pistons would push in .030, and the inner pistons would also push in .030. the guy I got the rotor from tried to tell me that my soft pedal that would pump up solid was not because of his out of round rotor, and that I had other problems (but agreed to send me another rotor anyway) I then pointed out to him that with a combined piston area of 7.76 in just one caliper, that I needed several inches of stroke out of the master with just 1" of area just to push the pads back out a combined distance of .060. yes, when calculating pressures, you only use 2 pistons of the 4, because they offset and push against each other, but when you're talking about piston movement to take up the distance from them being pushed back into the caliper by the wobbly rotor, you have to account for ALL of the pistons. anyway, despite him trying to tell me that I had 'other problems causing my soft pedal" a new rotor with nearly zero runnout fixed my issue. Photobucket sucks

Re: Brake bias and caliper BORE size. [Re: 70Cuda383] #1233110 05/17/12 08:23 PM 05/17/12 08:23 PM
Joined: Jan 2003 Posts: 3,704 MICHIGAN DynoDave master
DynoDave master Joined: Jan 2003 Posts: 3,704 MICHIGAN	This is a good read. I'm sorry it's at Frankenduster's expense, but I'm learning quite a bit. And some o fit, honestly, leaves me in a fog. I wish some of feets' math could be put into a spreadsheet with formulas...put in the value, get the ratio/value out. But I guess it's not that simple. DynoDave Walter P. Chrysler Club - Great Lakes Region Member # 12304 1970 Plymouth Duster 1972 Dodge Charger Rallye https://wichargerguy.proboards.com/ 1977 Chrysler Cordoba

Re: Brake bias and caliper BORE size. [Re: DynoDave] #1233111 05/17/12 08:37 PM 05/17/12 08:37 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Quote: This stuff leaves me in a fog. I wish some of feets' math could be put into a spreadsheet with formulas...put in the value, get the ratio/value out. But I guess it's not that simple. I thought that I was pretty decent at math. I should clarify... I am pretty decent at ARITHMETIC. The stuff Feets put up is over my head! I finished the RETURN to power brakes. The car has brake DIVE once again! WOW! All the cussing and frustration.... GONE. I had another couple of posts in the standard Q&A forum. In one of them, a helpful member listed a link to a vacuum can from Summit racing equipment. It was suggested to me a while back. I should have listened. Its sad that I didn't figure it out. I looked at the distribution block that I had with the manual setup. I couldn't find anything wrong with it. All this speculation about pedal ratios and caliper force is good diagnostic efforts, but at this point, the problem remains a mystery!

Re: Brake bias and caliper BORE size. [Re: DynoDave] #1233112 05/17/12 11:04 PM 05/17/12 11:04 PM
Joined: Jan 2003 Posts: 28,067 Irving, TX feets Senior Management
feets Senior Management Joined: Jan 2003 Posts: 28,067 Irving, TX	Quote: This is a good read. I'm sorry it's at Frankenduster's expense, but I'm learning quite a bit. And some o fit, honestly, leaves me in a fog. I wish some of feets' math could be put into a spreadsheet with formulas...put in the value, get the ratio/value out. But I guess it's not that simple. It's really simple math. I've pretty good with numbers but when they started putting letters in there I got lost. The most difficult thing to do is find the area of a circle. It's the radius of the circle multiplied by the radius of the circle then multiplied by 3.14. If the circle is 3 inches across, the radius is 1.5 inches. 1.5 inches times 1.5 inches times 3.14 2.25 inches times 3.14 7.065 square inches. Other than that, you're simply playing with numbers. I really thought about putting them into a spreadsheet just to play with later. To be perfectly honest, getting too hard core into the numbers can leave you chasing a perfection that you will never find. As for Frankenberry, I'm glad he got the brakes worked out. We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon

Re: Brake bias and caliper BORE size. [Re: feets] #1233113 05/18/12 08:48 AM 05/18/12 08:48 AM
Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O 70Cuda383 Too Many Posts
70Cuda383 Too Many Posts Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O	Quote: To be perfectly honest, getting too hard core into the numbers can leave you chasing a perfection that you will never find. Or, in my case, you could run all the numbers, calculate that you need a 7/8" bore master cylinder for that perfect pedal effort on a manual setup, only to have the "expert" at the brake store tell you that you're wrong, and that every manual disc combo really needs a minimum of a 1" bore for fluid volume. I had a pedal that was too stiff, and I never could lock up the fronts, although I was able to make it stop very hard, so I wasn't too concerned about it. just annoyed that I allowed myself to be talked out of what I wanted because the guy posed himself as an expert who deals with this all the time Photobucket sucks

Re: Brake bias and caliper BORE size. [Re: 70Cuda383] #1233114 05/18/12 03:46 PM 05/18/12 03:46 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	It seems as if there are enough variables in NON stock brake setups that there are no hard and fast rules. This reminds me of why "crate" engines became so popular. Sometimes it simplifies things to have a self contained, well engineered system for people that have more money than expertise!

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #1233115 05/18/12 06:54 PM 05/18/12 06:54 PM
Joined: Sep 2007 Posts: 14,889 up yours Supercuda About to go away
Supercuda About to go away Joined: Sep 2007 Posts: 14,889 up yours	You realize that with the power setup you lessen leverage and increase stroke for a given amount of pedal movement. Your fluid volume was too little with the manual setup, ergo my recommendation to upsize the MC. You get more volume one of two ways, longer stroke, or larger bore. They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.

Re: Brake bias and caliper BORE size. [Re: 70Cuda383] #1233116 05/18/12 07:08 PM 05/18/12 07:08 PM
Joined: Jan 2003 Posts: 28,067 Irving, TX feets Senior Management
feets Senior Management Joined: Jan 2003 Posts: 28,067 Irving, TX	Quote: Quote: To be perfectly honest, getting too hard core into the numbers can leave you chasing a perfection that you will never find. Or, in my case, you could run all the numbers, calculate that you need a 7/8" bore master cylinder for that perfect pedal effort on a manual setup, only to have the "expert" at the brake store tell you that you're wrong, and that every manual disc combo really needs a minimum of a 1" bore for fluid volume. I had a pedal that was too stiff, and I never could lock up the fronts, although I was able to make it stop very hard, so I wasn't too concerned about it. just annoyed that I allowed myself to be talked out of what I wanted because the guy posed himself as an expert who deals with this all the time It's kinda funny. As your master cylinder size goes up your pedal effort goes up but the brake pressure goes down. We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon

Re: Brake bias and caliper BORE size. [Re: feets] #1233117 05/18/12 07:11 PM 05/18/12 07:11 PM
Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O 70Cuda383 Too Many Posts
70Cuda383 Too Many Posts Joined: Oct 2003 Posts: 21,345 Marysville, O-H-I-O	Quote: Quote: Quote: To be perfectly honest, getting too hard core into the numbers can leave you chasing a perfection that you will never find. Or, in my case, you could run all the numbers, calculate that you need a 7/8" bore master cylinder for that perfect pedal effort on a manual setup, only to have the "expert" at the brake store tell you that you're wrong, and that every manual disc combo really needs a minimum of a 1" bore for fluid volume. I had a pedal that was too stiff, and I never could lock up the fronts, although I was able to make it stop very hard, so I wasn't too concerned about it. just annoyed that I allowed myself to be talked out of what I wanted because the guy posed himself as an expert who deals with this all the time It's kinda funny. As your master cylinder size goes up your pedal effort goes up but the brake pressure goes down. Yup! which is why I was so hesitant after doing my own calculations and decided a 7/8" was what I needed, but started to doubt myself when the "expert" told me I needed a 1" bore. then once I started driving it, I was annoyed that my pedal effort was harder than I wanted, but not annoyed to the point of wanting to change it Photobucket sucks

Re: Brake bias & caliper BORE size. Problem found? [Re: 70Cuda383] #1233118 05/19/12 02:34 AM 05/19/12 02:34 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	This is the last manual master cylinder that I used. I got it from Dr Diff. Nice looking piece... 15/16", Aluminum with plastic reserviors, very light. The fitting sizes were sorta small though. 7211960-DSCN1367.JPG (137 downloads)

Re: Brake bias & caliper BORE size. Problem found? [Re: Kern Dog] #1233119 05/19/12 02:37 AM 05/19/12 02:37 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	The 3/8" fittings posed a small problem. The combo block used a larger inlet fitting for the front line. I had to use an adapter. 7211962-DSCN1368.JPG (131 downloads)

Re: Brake bias & caliper BORE size. Problem found? [Re: Kern Dog] #1233120 05/19/12 02:39 AM 05/19/12 02:39 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	This is the inlet of the adapter. I'm wondering if this thing caused some sort of restriction...? 7211963-DSCN1371.JPG (137 downloads)

Re: Brake bias & caliper BORE size. Problem found? [Re: Kern Dog] #1233121 05/19/12 02:41 AM 05/19/12 02:41 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Outlet 7211965-DSCN1372.JPG (122 downloads)

Re: Brake bias & caliper BORE size. Problem found? [Re: Kern Dog] #1233122 05/19/12 02:51 AM 05/19/12 02:51 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	As stated, the facts elsewhere just dont add up to explain the problems with the manual setup. Pedal ratio would have been the same with the 4 wheel drums that the car had long before. The front brake line needed to be 3/8" at the master and 9/16" at the combo valve. I am terrible at flaring such small tubing, so I paid a guy to put a 9/16" fitting into a new brake like that had 3/8" fitting on the other end. HIS flaring skills were not any better than mine and the line leaked. THAT is why I used that adapter. Feets, 383Cuda.... ANYONE have an opinion on the chance that THIS is the problem? I just can't seem to let this one go.....!

Re: Brake bias & caliper BORE size. Problem found? [Re: Kern Dog] #1233123 05/19/12 02:55 AM 05/19/12 02:55 AM
Joined: Jan 2003 Posts: 28,067 Irving, TX feets Senior Management
feets Senior Management Joined: Jan 2003 Posts: 28,067 Irving, TX	Many master cylinders use larger fittings on one line. However, the lines themselves are the same size. It keeps people from installing the lines incorrectly. If the adapter you used did not reduce the fluid passage below the size of the line I don't see where it would have been a problem. We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon

Re: Brake bias & caliper BORE size. Problem found? [Re: feets] #1233124 01/26/14 05:09 AM 01/26/14 05:09 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	I really wish that I had an answer for this. Its been almost 2 years since I started this thread and I still think about it. Some thought my pedal ratio was wrong for manual brakes to work. I responded, saying the pedal ratio is identical to what the car had when I bought it with 4 wheel drums. I tried 4 different non power master cylinders with different bore sizes and every one sucked. Hard pedal and poor stopping. I thought of taking a spare brake pedal and drilling a new hole, higher toward the pivot point. This would increase the ratio. This would make for less effort, but would it be enough?

Re: Brake bias & caliper BORE size. Problem found? [Re: Kern Dog] #1233125 01/26/14 04:30 PM 01/26/14 04:30 PM
Joined: Jan 2007 Posts: 7,664 IN A ahy master
ahy master A Joined: Jan 2007 Posts: 7,664 IN	In part it comes down to weight and size. Your B body is heavier than the A you are comparing to so that gives the A an advantage. On line pressure, making the master bore smaller increases pressure but risks running out of volume. In the spirit of being a bit conservative I wouldn't want to go smaller than recommended and maybe sometime run out of volume. Also I wouldn't personally modify the linkage. Lots of design and testing went into it to make it robust. Also pads. For around town driving with cool brakes, the low cost organic pads have more bite than anything. The higher end DD type pads also have good bite (think parts store "gold"). Standard grade semi-metallic and performance pads have the least bite when cool... but hang in there well when hot. Also vacuum. Sounds like you have a bigger cam and lower vacuum. PB work best with 18+ vacuum. Anything over 10 or 12 is usually enough for putting around but max assist needs more vacuum. One test would be to get up to speed and downshift so the engine is spinning>2000 RPM with throttle closed. At that point it should be making good vacuum. Are the brakes noticeably better? In your case, I'll suggest maybe a pad change would help or more boost. An 8" double booster would give roughly 50% more boost compared to a 9" single. Or hydroboost which would also take vacuum out of the equation. I've got a similar opportunity. I've got 13" Baer brakes up front. Piston area is smaller than OE and the 9" booster does not have enough "oomph". The brakes work very well but I run out of boost before I run out of brakes. I'll likely do the double booster or hydroboost. My preference is the hydroboost as its lighter, more compact and provides more pressure. It's just spendy.

Re: Brake bias & caliper BORE size. Problem found? [Re: ahy] #1233126 01/26/14 05:56 PM 01/26/14 05:56 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Quote: Also vacuum. Sounds like you have a bigger cam and lower vacuum. PB work best with 18+ vacuum. Anything over 10 or 12 is usually enough for putting around but max assist needs more vacuum. One test would be to get up to speed and downshift so the engine is spinning>2000 RPM with throttle closed. At that point it should be making good vacuum. Are the brakes noticeably better? At speed, the brakes work fantastic. While rolling along at parking lot speeds, they are not good. I'm sure is related to engine vacuum. It is exactly because of this that I am still curious as to how I could make a manual brake combination work.

Re: Brake bias & caliper BORE size. Problem found? [Re: Kern Dog] #1233127 01/27/14 12:38 AM 01/27/14 12:38 AM
Joined: Jan 2007 Posts: 7,664 IN A ahy master
ahy master A Joined: Jan 2007 Posts: 7,664 IN	Sounds like adding an electric vacuum pump would fix it for good. 18"+ all the time. Master Power Brakes, Summit or others carry them. A few cars had them as original equipment so it may be possible to find one in a JY.

Re: Brake bias & caliper BORE size. Problem found? [Re: Kern Dog] #1233128 01/27/14 09:13 PM 01/27/14 09:13 PM
Joined: Jan 2003 Posts: 28,067 Irving, TX feets Senior Management
feets Senior Management Joined: Jan 2003 Posts: 28,067 Irving, TX	I don't understand why you had a problem with manual brakes. I've got large diameter multi-piston manual brakes and the pedal feel is equivalent to that of the modern performance cars I deal with at work. We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon

Re: Brake bias & caliper BORE size. Problem found? [Re: feets] #1233129 01/27/14 10:13 PM 01/27/14 10:13 PM
Joined: Aug 2013 Posts: 106 Central IL T Trojmn member
Trojmn member T Joined: Aug 2013 Posts: 106 Central IL	maybe i missed it, but you do or do not have a rear proportioning valve? if im thinking about this correctly, rear disk would want much higher line pressure than rear drums.

Re: Brake bias & caliper BORE size. Problem found? [Re: Trojmn] #1233130 01/28/14 01:04 AM 01/28/14 01:04 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	I agree. The system is plumbed like a 4 wheel drum setup with what was originally a drum distribution block. I tried 4 wheel drum versions, a few disc/drum versions and found zero difference between any of them. The electric vacuum pump may be the answer. I'd prefer to simplify the system but unless I can figure out the reasonong for the poor performance of the manual setup, it seems that I am limited in my choices.

Re: Brake bias and caliper BORE size. [Re: feets] #3058760 07/13/22 03:02 AM 07/13/22 03:02 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Originally Posted by feets Or, in my case, you could run all the numbers, calculate that you need a 7/8" bore master cylinder for that perfect pedal effort on a manual setup, only to have the "expert" at the brake store tell you that you're wrong, and that every manual disc combo really needs a minimum of a 1" bore for fluid volume. I had a pedal that was too stiff, and I never could lock up the fronts, although I was able to make it stop very hard, so I wasn't too concerned about it. just annoyed that I allowed myself to be talked out of what I wanted because the guy posed himself as an expert who deals with this all the time It's kinda funny. As your master cylinder size goes up your pedal effort goes up but the brake pressure goes down. [/quote] Here I am, ten years later and I'm revisiting this same issue. I have the engine, trans, K member and suspension out of the car. I pulled the power brake booster and MC and swapped in another 15/16" MC from Dr Diff but I have a drum-drum distribution block. A video online featuring a crash involving a 64 Mercury Comet really shed light on the importance of upgraded brakes for high performance cars. I'm also looking into the Dr Diff 13" front brake kit.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3059021 07/13/22 08:19 PM 07/13/22 08:19 PM
Joined: Jan 2003 Posts: 30,989 Oregon A AndyF I Win
AndyF I Win A Joined: Jan 2003 Posts: 30,989 Oregon	I've been using 13 inch front rotors on my Mopar projects for more than 20 years. Maybe close to 30 years, I've actually lost track on when I did my first big brake conversion. The 13 inch front rotors make the car so much easier to drive that I doubt I'd ever go back to a factory size brake. Especially when it is so easy to make power these days. The engine in my Coronet made over 600 hp even though it has a very modest hyd roller cam and the compression ratio is 9.8 for pump gas use. With that much power the car needs good brakes. It is just too easy to get into trouble with 600 hp on tap.

Re: Brake bias and caliper BORE size. [Re: AndyF] #3059033 07/13/22 09:05 PM 07/13/22 09:05 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Andy, maybe you can help me understand something. The Dr Diff Cobra kit uses a 2 piston caliper with 1.5" bore calipers. The math states that the surface area of the pistons is 3.53 square inches. My 2.75" single piston iron caliper has a surface area of 5.93" I'm having trouble understanding how the 2 piston caliper with a smaller surface area can provide more clamping force than the big single piston caliper. I thought about it and was thinking that maybe the 2 piston calipers require less fluid volume to move the same amount that the larger one does.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3059051 07/13/22 10:45 PM 07/13/22 10:45 PM
Joined: Jan 2003 Posts: 30,989 Oregon A AndyF I Win
AndyF I Win A Joined: Jan 2003 Posts: 30,989 Oregon	Nothing wrong with your math, the factory 2.75 piston is huge compared to anything used in later model cars or the aftermarket. That is why you have to go with a smaller piston in the MC when you switch to aftermarket brakes. Everything has to be smaller to work out correctly. Use a smaller MC piston and use a larger rotor (I prefer 13 inch rotors with 17 inch rims) and you'll have a much better braking system than anything the factory used during the muscle car era.

Re: Brake bias and caliper BORE size. [Re: AndyF] #3059073 07/14/22 01:59 AM 07/14/22 01:59 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Thank you. I have 18" wheels so the 13" front rotors and caliper will clear easily. Finding a spare that will clear may be tricky though!

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3059266 07/14/22 06:17 PM 07/14/22 06:17 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	I am starting to understand it a little better but it still seems strange that a smaller surface area in terms of piston caliper sizing can provide more clamping force.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3059275 07/14/22 06:52 PM 07/14/22 06:52 PM
Joined: May 2005 Posts: 4,703 Florida BDW master
BDW master Joined: May 2005 Posts: 4,703 Florida	haven't read the whole thread, I would think the larger rotor would yield the biggest improvement, even with a small caliper Leverage is king, the further outward the caliper, the better. "Give me a long enough lever, and I can move the world" Not sure said that, but you get the idea

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3059279 07/14/22 07:04 PM 07/14/22 07:04 PM
Joined: May 2019 Posts: 6,215 nowhere S Sniper master
Sniper master S Joined: May 2019 Posts: 6,215 nowhere	Originally Posted by Kern Dog I am starting to understand it a little better but it still seems strange that a smaller surface area in terms of piston caliper sizing can provide more clamping force. It doesn't, in the caliper. Andy said in the Master cylinder though.

Re: Brake bias and caliper BORE size. [Re: Sniper] #3059290 07/14/22 08:48 PM 07/14/22 08:48 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Originally Posted by Sniper Originally Posted by Kern Dog I am starting to understand it a little better but it still seems strange that a smaller surface area in terms of piston caliper sizing can provide more clamping force. It doesn't, in the caliper. Andy said in the Master cylinder though. Here is where I am hung up.. My car currently has the Cordoba 11.75 rotors and 2,75" single piston front calipers. Going to a larger rotor makes sense regarding leverage. I am trying to understand how a caliper with less surface area could provide equal to or greater clamping force IF the master cylinder size is the same for both.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3059366 07/15/22 09:58 AM 07/15/22 09:58 AM
Joined: May 2019 Posts: 6,215 nowhere S Sniper master
Sniper master S Joined: May 2019 Posts: 6,215 nowhere	Originally Posted by Kern Dog Originally Posted by Sniper Originally Posted by Kern Dog I am starting to understand it a little better but it still seems strange that a smaller surface area in terms of piston caliper sizing can provide more clamping force. It doesn't, in the caliper. Andy said in the Master cylinder though. Here is where I am hung up.. My car currently has the Cordoba 11.75 rotors and 2,75" single piston front calipers. Going to a larger rotor makes sense regarding leverage. I am trying to understand how a caliper with less surface area could provide equal to or greater clamping force IF the master cylinder size is the same for both. Not sure where you got the idea a smaller bore caliper will have more clamping force.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3059372 07/15/22 10:42 AM 07/15/22 10:42 AM
Joined: Jan 2003 Posts: 30,989 Oregon A AndyF I Win
AndyF I Win A Joined: Jan 2003 Posts: 30,989 Oregon	Originally Posted by Kern Dog Originally Posted by Sniper Originally Posted by Kern Dog I am starting to understand it a little better but it still seems strange that a smaller surface area in terms of piston caliper sizing can provide more clamping force. It doesn't, in the caliper. Andy said in the Master cylinder though. Here is where I am hung up.. My car currently has the Cordoba 11.75 rotors and 2,75" single piston front calipers. Going to a larger rotor makes sense regarding leverage. I am trying to understand how a caliper with less surface area could provide equal to or greater clamping force IF the master cylinder size is the same for both. It won't. The smaller pistons will reduce clamping force. You need to reduce the MC bore size to rebalance the system and then you need to change the rear wheel cylinder size so it isn't isn't out of whack. Most people fail at either step one or step two of this process. You at least are thinking about it so you're a step ahead of most.

Re: Brake bias and caliper BORE size. [Re: AndyF] #3059385 07/15/22 12:07 PM 07/15/22 12:07 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	I am trying to understand how and why a switch from a 12 inch setup to the 13 inch setup would provide a gain. If the larger rotor provides more leverage but the smaller caliper size isn't as effective, why wouldn't they increase the caliper size ? Is there so much gain in the leverage that it greatly offsets the loss from a smaller caliper?

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3059409 07/15/22 01:34 PM 07/15/22 01:34 PM
Joined: Sep 2003 Posts: 19,307 north of coder moparx "Butt Crack Bob"
moparx "Butt Crack Bob" Joined: Sep 2003 Posts: 19,307 north of coder	the brake info sticky at the top by member feets is a very good source of understanding the workings of the brake system. at least in my opinion it is.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3059441 07/15/22 03:14 PM 07/15/22 03:14 PM
Joined: Jan 2003 Posts: 30,989 Oregon A AndyF I Win
AndyF I Win A Joined: Jan 2003 Posts: 30,989 Oregon	Originally Posted by Kern Dog I am trying to understand how and why a switch from a 12 inch setup to the 13 inch setup would provide a gain. If the larger rotor provides more leverage but the smaller caliper size isn't as effective, why wouldn't they increase the caliper size ? Is there so much gain in the leverage that it greatly offsets the loss from a smaller caliper? You are mixing and matching parts so there is no logic to the question. If you look at a late model car with 13 inch rotors you'll see that the MC bore size and the piston caliper sizes are all on the small size. The engineers figured out a few years back that if everything was smaller then it could all be lighter but still provide the clamping forces required to stop the car. The old 2.75 caliper used by Mopar back in the 70's doesn't really exist anymore. Now everything uses multiple pistons and small bore sizes.

Re: Brake bias and caliper BORE size. [Re: AndyF] #3059458 07/15/22 04:22 PM 07/15/22 04:22 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	We must be speaking different languages here because no matter what I write, I'm not getting the answers directly to what I am asking. I feel like I'm dealing with lawyers here. I have mixed and matched stuff in the past but am trying to get a matched system going BUT want to know why and how it works. Don't you guys have any natural curiosity about how things work? Maybe you don't understand it either but won't admit it? Andy...I read your response about smaller and matched components on newer factory systems. I'm trying to understand why the old setup could have had a boosted 15/16" master cylinder and 2,75" calipers and an aftermarket setup can have the same sized MC, smaller calipers (Larger rotors) and somehow provide better stopping. Even the stock manual disc/drum A body cars had a MC with a 1 inch bore or something close to that. I'm not broke and pinching pennies here.....I just like to know that I'm not spending time and money to see no results. I want to know the how and why. I'm like this with everything even if it is free.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3059504 07/15/22 07:52 PM 07/15/22 07:52 PM
Joined: Jan 2003 Posts: 30,989 Oregon A AndyF I Win
AndyF I Win A Joined: Jan 2003 Posts: 30,989 Oregon	The new designs are more rigid so you end up with better brakes even though the clamping force might be a little less. The old school mopar cast iron 2.75 inch caliper isn't super rigid so there might be some clamping force lost just due to the design. The cars that I've built over the last 10 years have all had 13 inch rotors (1.25 thick) with either Viper or Porsche calipers. I then use a small 15/16 diameter MC and if I'm using drum brakes in the rear I use the smallest wheel cylinder out back. Those systems work great. The brake pedal feels very firm and the car sucks down hard when you lean on the brakes. The factory 11.75 systems that I've used in the past didn't stop nearly as well. Some of the difference might also be due to brake pad material. There aren't many options for the old mopar calipers while you can find at least a dozen different pad compounds for a Viper caliper. Porsche big red calipers have even more choices.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3059507 07/15/22 07:57 PM 07/15/22 07:57 PM
Joined: May 2019 Posts: 6,215 nowhere S Sniper master
Sniper master S Joined: May 2019 Posts: 6,215 nowhere	It's basic math and physics. I will run thru it for you. For a master cylinder you apply a force to the piston which tries to compress the brake fluid. The pressure increase in the brake fluid is determined by the surface area of the piston and the force you apply to it. The formula for determining the area of the piston is 3.1415 time the radius squared. For a 1 inch bore master cylinder the area is 0.78 square inches. For a 15/16 inch bore master cylinder the area is 0.69 square inches. How does the smaller bore makes more pressure? You are applying the same force to both. To start with let us assume there is a third bore size that equals 1 square inch of area. Apply 100 lbs of force to that you get 100lbs per square inch. Since the two examples are smaller than 1 square inch you have to calculate how much pressure is being created by understanding that the force applied to each example needs to be corrected to account for the smaller bore size in relationship to one square inch. The formula for that is to divide 1 by the area of the bore you are using. 1 in bore is 1/0.78 = 1.27 15/16 inch bore is 1/0.69 = 1.44 These are the ratios to correct the smaller bore sizes so that they would match a 1 square inch area. We do this so that the end value (pressure out of the master cylinder) can be read as pounds per square inch. Now let's apply a force to these two sizes, we will use 100 lbs of force, your foot, to make the math easy. The formula at this point is 100 (force from your foot) times the ratios we calculated. 1 in bore is 100 * 1.27 = 127 lbs per square inch. 15/16 inch bore is 100 * 1.44 = 144 lbs per square inch. Now the caliper end of things works similarly, but in the opposite direction. You have a 2.75" caliper piston bore we will need to calculate the area, same formula as above for area, 3.1415 time the radius squared. Radius of 2.75 is 1.375, square it then times 3.1514 equals 5.94 square inches of piston area. If you apply the 127 PSI from the 1" bore master cylinder to the caliper piston you get 754 psi on the caliper piston. (formula is pressure into the caliper times caliper piston area) If you apply the 144 PSI from the 15/16" bore master cylinder to the caliper piston you get 855 psi on the caliper piston. It's all a case of hydraulic leverage. We will not be getting into the mechanical leverage imparted by the brake pedal pivot points.

Re: Brake bias and caliper BORE size. [Re: Sniper] #3059509 07/15/22 08:07 PM 07/15/22 08:07 PM
Joined: May 2019 Posts: 6,215 nowhere S Sniper master
Sniper master S Joined: May 2019 Posts: 6,215 nowhere	An addendum to the above regarding multiple piston calipers. You have to calculate the area of all the pistons involved (some setups use staggered piston sizing) then add those together to come up with the total caliper piston area then you can do the pressure times area math. For example, some Mustang calipers use two 1.5" pistons. In this case it would be ((3.1415 times the radius squared) times two) so 1.76" area for each piston times two pistons equals 3.54 square inches total. This is much smaller than the 5.94 square inches of the Mopar 2.75" bore caliper. So pressure on the pistons will be less. But that application (96 Stang) uses a 13" rotor so force at the wheel may be comparable, not doing that math, lol.

Re: Brake bias and caliper BORE size. [Re: Sniper] #3059519 07/15/22 08:25 PM 07/15/22 08:25 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Thanks, guys. I'm just very curious and the boundaries of a non face-to-face meeting make it hard to exchange ideas sometimes. I do understand the math of it. I've read the contributions Feets provided as well. I'm getting the impression that the leverage of the larger sized rotors is where the majority of the improvements are. The thicker rotor width provides a longer duration before they overheat. Newer cars have greater development of pad compounds available too from what I gather. Since this is a classic car forum, I figure that most of us are modifying old cars one end at a time. Years back, I pulled the stock and perfectly functioning 10" rear drums to install the Dr Diff 10.7" rear disc kit. This was done purely for appearance reasons. I wanted the look of a disc rotor through the wheel spokes. It turns out it didn't make any difference in how the car stopped. Braking performance was the same. That wasn't a bad thing....the brakes weren't terrible before or after. I went from what was probably a 15/16" wheel cylinder to a 1.5" single piston caliper. This is surely apples to oranges but I recall reading that when one had rear wheel lockup with drum brakes, the trick is to use smaller wheel cylinders. Well, a larger sized caliper piston would seem to be expected to provide more clamping force there too.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3059550 07/15/22 10:48 PM 07/15/22 10:48 PM
Joined: Jan 2003 Posts: 30,989 Oregon A AndyF I Win
AndyF I Win A Joined: Jan 2003 Posts: 30,989 Oregon	If you were closer I'd just have you drive my Coronet so you could see what you think. I can tell you that my Coronet stops better than my Toyota 4Runner which has factory power 4 wheel disc brakes. I can exit the freeway at 80 mph in the Coronet and it will immediately pull down to 35 or 25 as I approach stopped traffic. With the 4Runner I have to be careful to leave plenty of stopping distance when slowing down from anything over 70 mph. My Coronet has 13 inch front rotors with Porsche calipers. I added a rear disc kit a few years back but I think the factory drum brakes that I had on there before worked better than the disc brakes. I had the big station wagon drums out back and they really worked. Last edited by AndyF; 07/15/22 10:50 PM.

Re: Brake bias and caliper BORE size. [Re: AndyF] #3059579 07/16/22 01:06 AM 07/16/22 01:06 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	That is what I want....brake confidence like I have felt in newer cars. The 72 Duster stops better than any classic car I've owned and it is a basic manual MC 11" disc 10" drum setup with 2.75" calipers. That car is what gives me hope that I can make the Charger stop as well or better if the right selection of parts is found. Dr Diff suggests his 13" Cobra front kit and the 11.7" rear along with either a 15/16" manual MC or a hydroboost with a 1 1/8" MC.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3059613 07/16/22 09:05 AM 07/16/22 09:05 AM
Joined: May 2019 Posts: 6,215 nowhere S Sniper master
Sniper master S Joined: May 2019 Posts: 6,215 nowhere	If you can lock your brakes up you already have more brakes than tire. You can update your brakes all day long, but unless you have the tires to use that added braking power you are wasting time. So unless you need the added thermal mass of larger brakes look to tire size increases first. If you already have fitting the biggest tire you can then yes it makes sense to update the brakes, assuming you can no longer lock them up, lol.

Re: Brake bias and caliper BORE size. [Re: Sniper] #3059655 07/16/22 12:27 PM 07/16/22 12:27 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Tire size is not a problem.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3059656 07/16/22 12:28 PM 07/16/22 12:28 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	I don't recall the last time that I was able to or actually did skid the brakes. Right now the engine is out for a rebuild but before I tore it down, the brakes worked okay but weren't impressive enough to brag about.

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3059680 07/16/22 02:31 PM 07/16/22 02:31 PM
Joined: May 2005 Posts: 4,703 Florida BDW master
BDW master Joined: May 2005 Posts: 4,703 Florida	I think the newer cars can use smaller calipers because of the larger rotors. Can't underestimate the leverage adder, plus as mentioned, I'm sure the new pads are much better than the old stuff. Just think of how easy it is to break a bolt free after you slide a pipe on the rachet to extend it.....

Re: Brake bias and caliper BORE size. [Re: BDW] #3059931 07/17/22 01:53 PM 07/17/22 01:53 PM
Joined: Sep 2003 Posts: 19,307 north of coder moparx "Butt Crack Bob"
moparx "Butt Crack Bob" Joined: Sep 2003 Posts: 19,307 north of coder	and speaking of pads, how do the ceramic types compare to the semi-metallic of back in the day, as compared to "red stuff", "yellow stuff", etc that EBC offers ? this is in relation to the small rotor size needed to fit 15" wheels. i have read all the descriptive attributes of the above mentioned pads, as well as what is offered by Hawk and other race type pad manufacturers, but i am hesitant to pull the plug on a set of pads, only to find out they may or may not, work to my expectations.

Re: Brake bias and caliper BORE size. [Re: BDW] #3059980 07/17/22 04:41 PM 07/17/22 04:41 PM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Originally Posted by BDW I think the newer cars can use smaller calipers because of the larger rotors. Can't underestimate the leverage adder. Just think of how easy it is to break a bolt free after you slide a pipe on the rachet to extend it..... Excellent point. Could it be that simple?

Re: Brake bias and caliper BORE size. [Re: Kern Dog] #3060263 07/18/22 03:23 PM 07/18/22 03:23 PM
Joined: May 2019 Posts: 6,215 nowhere S Sniper master
Sniper master S Joined: May 2019 Posts: 6,215 nowhere	Originally Posted by Kern Dog Originally Posted by BDW I think the newer cars can use smaller calipers because of the larger rotors. Can't underestimate the leverage adder. Just think of how easy it is to break a bolt free after you slide a pipe on the rachet to extend it..... Excellent point. Could it be that simple? ABS probably has an effect as well. While I can no longer remember the details I do recall an article Eberg wrote comparing the brakes on his Green Brick vs sports cars of the time it was written. Can't seem to google it though. I don;t recall it being real fancy though it might have has one of AndyF's Viper caliper setups on it.

Re: Brake bias, caliper BORE size and PAD recomendations... [Re: Kern Dog] #3060359 07/18/22 08:18 PM 07/18/22 08:18 PM
Joined: Aug 2003 Posts: 43,097 Bend,OR USA C Cab_Burge I Win
Cab_Burge I Win C Joined: Aug 2003 Posts: 43,097 Bend,OR USA	How much does that Duster weigh? How much does your Charger weigh? Bigger cars need more brakes(bigger contact area) to stop as good as lighter smaller cars do, basic physics Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)

Re: Brake bias and caliper BORE size. [Re: moparx] #3060887 07/20/22 11:16 AM 07/20/22 11:16 AM
Joined: Jan 2003 Posts: 1,231 Chicago, IL P PLUM_72 pro stock
PLUM_72 pro stock P Joined: Jan 2003 Posts: 1,231 Chicago, IL	Originally Posted by moparx and speaking of pads, how do the ceramic types compare to the semi-metallic of back in the day, as compared to "red stuff", "yellow stuff", etc that EBC offers ? this is in relation to the small rotor size needed to fit 15" wheels. i have read all the descriptive attributes of the above mentioned pads, as well as what is offered by Hawk and other race type pad manufacturers, but i am hesitant to pull the plug on a set of pads, only to find out they may or may not, work to my expectations. This pad part of the thread seems to be getting lost and may need a thread of its own... 1972 Dodge Challenger

Re: Brake bias and caliper BORE size. [Re: PLUM_72] #3060898 07/20/22 11:34 AM 07/20/22 11:34 AM
Joined: Sep 2003 Posts: 19,307 north of coder moparx "Butt Crack Bob"
moparx "Butt Crack Bob" Joined: Sep 2003 Posts: 19,307 north of coder	good point.

Re: Brake bias and caliper BORE size. [Re: moparx] #3061154 07/21/22 01:05 AM 07/21/22 01:05 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog OP Striving for excellence
Kern Dog OP Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	The brake pad topic is a valid one and supports the inclination to change to a modern system. The Dr Diff stuff is based on OEM production calipers and rotors. This likely means that the brake pads might be available from the higher end aftermarket suppliers.

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