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Disc o tech - blues....my 4 wheel drums were better.
Posted By: plazomat
Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 02:49 AM
Just finished off a disc conversion using..
10.9 inch rotors - new
72 ebody pin calipers - new
72 ebody spindles (w/bearing adaper) - new
1 1/32 master - new
all new lines and hoses
10 * 1/3/4 drums out back, not new but in great shape.
no combination or proportioning valve.
Brakes just suck - low but hard pedal and I gotta stand on it to stop the car..
Brakes are bled I guess - no spongy but low and hard as hell pedal.
I know a combination valve is in order but will that fix the feel of the brakes? - which year/body valve should i get? Will a generic under master cyl gm unit work?
I guess I need a residual pressure valve in the rear lines as well - will that fix the pedal height?
What steps should I take to resolve this - I don't want to just throw a bunch more variables into this system and never get it right..
Thanks
Plaz
Posted By: DAYCLONA
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 02:55 AM
No mention of what type of master your using?, drum/drum?, disc/drum?, OEM?, aftermarket?
You'll need a proportioning valve...OEM or aftermarket, your choice
Power assist?, non power?
What pedal set up was used?
Are the rear drums adjusted properly? (travel)
Posted By: Challenger 1
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 03:05 AM
Quote:
Just finished off a disc conversion using..
10.9 inch rotors - new
72 ebody pin calipers - new
72 ebody spindles (w/bearing adaper) - new
1 1/32 master - new
all new lines and hoses
10 * 1/3/4 drums out back, not new but in great shape.
no combination or proportioning valve.
Brakes just suck - low but hard pedal and I gotta stand on it to stop the car..
Brakes are bled I guess - no spongy but low and hard as hell pedal.
I know a combination valve is in order but will that fix the feel of the brakes? - which year/body valve should i get? Will a generic under master cyl gm unit work?
I guess I need a residual pressure valve in the rear lines as well - will that fix the pedal height?
What steps should I take to resolve this - I don't want to just throw a bunch more variables into this system and never get it right..
Thanks
Plaz
What makes you think they will work without either valve in there? 
How do you have the lines junction ed together now?
Posted By: plazomat
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 03:07 AM
Thanks so much for the response..here's more info
Disc/Drum 1 1/32 unit for an 85 dippy - new parts store purchase coni seal brand
Manual - no power
Manual pedal setup that was in car since new - 4 wheel drums
Rear drums adjusted to slight drag
Only a proporting valve or a combo valve (prop/metering functions)
Just throw all parts at car or take in stages?
Plaz
Posted By: plazomat
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 03:17 AM
Quote:
What makes you think they will work without either valve in there?
How do you have the lines junction ed together now?
The stock drum/drum unit is in there - its just a distribution block and does not provide any valving or metering..
Plaz
Posted By: Supercuda
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 03:22 AM
You really didn't follow the disc-o-tech instructions, now did you.
The M/C is too larger of a diameter.
Posted By: moparpollack
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 03:24 AM
Pad material can affect stopping ability. My 64 Polara had the lifetime autozone pads that didn't stop for anything.
Posted By: plazomat
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 03:30 AM
Quote:
You really didn't follow the disc-o-tech instructions, now did you.
The M/C is too larger of a diameter.
Doesn't he recomend a master from a 76-8 F body? and aren't they 1 1/32? What am I missing here?
Posted By: DAYCLONA
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 03:46 AM
Quote:
Thanks so much for the response..here's more info
Disc/Drum 1 1/32 unit for an 85 dippy - new parts store purchase coni seal brand
Manual - no power
Manual pedal setup that was in car since new - 4 wheel drums
Rear drums adjusted to slight drag
Only a proporting valve or a combo valve (prop/metering functions)
Just throw all parts at car or take in stages?
Plaz
Feedback,...if you repeatedly pump the pedal, does it gain noticeable height?, or maintain about the same height, does maintaining depressed pedal pressure cause the pedal to slowly sink?
Posted By: plazomat
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 05:11 AM
Pumping does not change pedal feel at all.
Holding pedal down hard with foot, no sinking what so ever..
Plaz
Posted By: RapidRobert
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 05:39 AM
Quote:
no combination or proportioning valve.
Brakes just suck - low but hard pedal and I gotta stand on it to stop the car..
I think the low pedal is key & others have had to stand on the pedal (at normal height tho) with the wrong bore MC. In my case: 65 dart with 74 A discs (76-2.75 calipers) with aftermarket (ceramic? pads) and a 1&1/8 dual alum MC with adapter plate & 10" (7&1/4) rear drums and OE drum splitter (mismatched system) and it would put me in the windshield if I stood on it. I would put it up on stands have a helper spin the fronts as you work the pedal and idle it in gear & see how the rears act. Holler with any news. I'm thinking inadequate psi (line restriction somewhaere) if there is no mechanical malfunction at the corners but there is something going on/wrong with the low pedal (find/fix that). I had that exact same symptoms (height was OK tho) on the stock car from a braided line bent at too severe of an angle. EDIT Is the MC adapter plate what is making the pedal too low and post what the pedal ratio is
Posted By: plazomat
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 06:30 AM
Thanks for the input RR.
I was wondering about the adapter plate as well. I think its an AR engineering one with a step where the master bolts to..http://arengineering.com/products/master-cylinder-adapter-four-studs/
I will double check the lines for kinks and what not and figure out how to measure the pedal ratio..
Plaz
Posted By: Kern Dog
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 07:20 AM
Maybe I missed something but I don't recall the car you are working on....In addition, there are a few mistakes I see here.
NO Diplomat came with manual brakes. The master cylinder from a Diplomat is sized for power assist.
Any disc/drum system needs an actual proportioning valve. The front calipers use a much greater volume of fluid as compared to the rear. The stock Mopar disc/drum proportioning valve held off pressure to the rear until the FRONT built up pressure. By using what is known as a "distribution block", (No metering, just a junction for the brake lines) your calipers are only getting the volume and pressure that the old front wheel cylinders received. NOT good and nowhere near enough.
I have a bunch of actual disc/drum proportioning valves that would work. The ones from mid 70s A body cars are pretty easy to find and work well. PM me if you want a screaming deal on a used Prop valve.
Posted By: Kern Dog
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 07:29 AM
These are often called the "Texas" valve for obvious reasons. They are the ones I mentioned from a 73-76 A body.
Posted By: doctor_mopar
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 07:53 AM
I would say a smaller bore master cylinder is in order. Of course the proportioning valve also. Take not that a rebuild kit and instructions for the proportioning valve is available cheap from Muscle car research online.
Posted By: therocks
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 03:52 PM
I use nothing but 70C body masters.I run Ceramic pads with my pin types on the 65.Stops great and good pedal.The stock spliter will work if you use an adjustable PP valve to the rear.I use 5th Ave PP valves.Mine have been on at leats 15 years and no problems even at 120 it stops great.Rocky
Posted By: DAYCLONA
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 06:15 PM
After reading some of your feedback, and updates as to what the actual parts are, that are involved in your swap,...IMHO if you want to retain the 2 bolt aluminum F body master, put a booster behind it, and add a proportioning valve to the system, or if manual brakes are your desired goal, then toss the F body master and adapter plate and use a 70 B body or 70-4 E body master designed for manual disc brake application, and add a proportioning valve, if you wish to try/run the B/E body masters, just say so, and I can supply you with the PN# and specs so that you can make an informed choice regarding the proper sizing/application....I'll assume this is for your 69 Coronet?
mike
Posted By: BDW
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 06:41 PM
Isn't the factory manual disc/drum set-up a 1 1/16" MC?
Can't imagine it would make up the problems mentioned.
Why switch back from the nicer 2- bolt set- up?
Posted By: dogdays
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 08:48 PM
First things first, you need pads that actually work. Sounds like your pads aren't doing the job. They're easy and cheap to switch, unlike some of the other suggestions here.
DO the easy things first!
Less than $10 at Rockauto.
R.
Posted By: therocks
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 09:53 PM
10 buck pads cant be too good.My ceramics were 30 bucks like 8 years ago and that was shop price.They work better that the Bendix that cost more 15 years ago.Cheap pads are just that cheap period.Saw too many problems with cheap sets at the shop.Rocky
Posted By: John_Kunkel
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 10:42 PM
MC may be too large but a smaller MC will lower the pedal even more.
Adding a prop valve or RPV won't help the stopping problem.
Posted By: RapidRobert
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 10:43 PM
Plaz you had 4 wheel drums that were OK for what they were & you wanted better & kept the rear drums intact & swapped to the alum dual MC/discs up front (as stated in your parts list) with no other changes & it's worse now, is that correct?. The alum MC can have a thicker flange/more recessed piston position (possibly deeper "thimble" also) & then there's the thickness of Andys adapter plate all of which contribute to a lower pedal. An adjustable MP will take care of that. This is pretty much identical to what I had/did on my drum/drum dart converted to disc/drum & it was fine even with the big bore MC but others definitely have had issues with too big of bore in the MC but 1&1/32" doesn't sound to big
. Keep us posted. You had manual brakes before so pedal ratio ain't an issue. I would get the pedal height up but sounds like something else is going on. If you have only plumbed in new discs up front which is how I read it (then problem is up front (mc/discs) not in the splitter valve or in the rear drums) & your proportioning might be off (if anything the discs would be engageing too quick) but that ain't the issue going on. I would get the front wheels off the ground & grab a helper to spin the wheel(s) (for a start).
Posted By: cudaman1969
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 11:03 PM
I'm thinking the pads are glazed over, had drums do this alot. The best brakes i ever had where a-body(70 Duster) front disc and the largest drums in back, no power just the safety valve and stock drum master with no residual valve to the front, stop on a dime.
Posted By: plazomat
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 11:15 PM
Thanks guys for all the insight - just wanna make this thing safe to drive again.
Dayclona - would love to see your list - not set against power brakes, just didn't think it was needed..it is for a 1969 Plymouth B. I just like the look of the 2 bolt master, but if it has to go then so be it - I usually drive with the hood down anyway
Changing pads is quick and easy enough - what do you guys suggest for a pin type caliper - I think 2.75 piston - 72 ebody calipers.
Rapid Robert - you are correct that the drums in fine working order just wanted better....all hardlines are plumbed and new.
Pedal height - just to clear up what I mean. The pedal is physically at the right height, up tight against the brake light switch. It just does seem to grab until about half way down and then can't push it beyond 75% down - hard as a rock.
Feels like brakes have no bite..
Posted By: AndyF
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 11:23 PM
Maybe they don't have any bite. Could be glazed pads or glazed rotors. If you didn't bed them in correctly then you could have very low friction and not much stopping force.
You could have a variety of issues with the brake system but the overall design should work fine. You just need to figure out where the problem is.
The 11.75 rotors will work better on a big heavy car than the 10.90 rotors, but you should still be able to get the 10.9 system to stop the car effectively.
Posted By: Kern Dog
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 11:24 PM
The responses are all over the map here. LOTS of opinions.
I don't see how pads could get glazed if they never got hot enough to stop the car.
When a "custom" situation like this gives poor results, maybe a wise move is to mimic a setup that the factory used. Once you have a matched set of components, you have a better chance of success.
Here is what seems wrong from my point of view:
Wrong type of master cylinder for the application.
Lack of proper front/rear proportioning.
Again, the OP has not given all the information. Maybe I missed it?
Vehicle, brake size, caliper bore size, master cylinder adapter size and type, brake pedal pushrod length as compared to the original. Again, once you deviate from a factory setup, every single component results in a "variable" that can cause trouble if it is not correct for your application.
Trying to help with such little information is not easy. If you want help, you need to give more details.
Are you listening?
Posted By: Stanton
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 11:52 PM
Quote:
Pedal height - just to clear up what I mean. The pedal is physically at the right height, up tight against the brake light switch. It just does seem to grab until about half way down and then can't push it beyond 75% down - hard as a rock.
So the whole time you push the pedal its filling up the system because you haven't used the valves as advised. Start there.
When it gets "hard as a rock" is it possible you've totally compressed the cylinder in the m/c ?!?!?
What about the pushrod, what are you using and is it in full contact in the m/c with the pedal at full height? This can be an issue because the m/c spacer plate is a good 1/4" thick or more.
Keep in mind the pedal ratio here - if there is even a 1/8" of play in the pushrod it will take almost an inch of pedal just to take up that slack! On the flip side, are you sure that the pushrod isn't preloading the m/c ??
FWIW you want the pushrod in the m/c, bolt the m/c to the firewall then crawl in the car and install the pushrod to pedal bolt without having to move either the pedal or the pushrod to make it fit.
Posted By: RapidRobert
Re: Disc o tech - blues....my 4 wheel drums were better. - 10/31/14 11:59 PM
Quote:
Pedal height - just to clear up what I mean. The pedal is physically at the right height, up tight against the brake light switch. It just does seem to grab until about half way down and then can't push it beyond 75% down - hard as a rock. Feels like brakes have no bite..
We're on to something with this (clarification). I would buy a pair of brass inverted flare male fittings to cap the MC & if it is good (& bled out) the pedal will be rock hard with virtually NO travel. Those "Edelman" fittings are cheap & you will reuse em. How about we get the MC cleared away as the culprit (I think it is guilty). It ain't the pads. with my (earlier mentioned) dart that is somewhat similar to your conversion there is a very slight bit of pedal travel & it's rock hard. EDIT If you have a MC fitting/line pigtail handy you might flatten the line end & install it in the disc port & see if the pedal is now rock hard/virtually no travel. OP post what it ends up being cuz we got bets on this one 
Posted By: DAYCLONA
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/01/14 12:25 AM
Quote:
Thanks guys for all the insight - just wanna make this thing safe to drive again.
Dayclona - would love to see your list - not set against power brakes, just didn't think it was needed..it is for a 1969 Plymouth B. I just like the look of the 2 bolt master, but if it has to go then so be it - I usually drive with the hood down anyway
Personally, I'd go with a 1 1/8" bore master intended for manual disc applications which the majority were equipped with 10" rear drums, and a proportioning valve, either factory or aftermarket adjustable....just my opinion
Mike
Posted By: Fury Fan
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/01/14 05:32 PM
The bigger the bore, the higher the pedal effort for manual brakes (and longer required pedal travel -- but long pedal travel can be caused by other 'errors' in the installation). Would be the same rule for PB also, but you might not feel the difference as the booster might mask it.
I put manual DB on my 68 Fury and used a MC from a mid-70s 1/2-ton truck with MDisc. Don't know the bore, but I know it's on the smaller end. Same pedal feel as MDrum but significantly improved braking.
I feel there's a typo or some add'l info missing in that chart above. 1-1/8 is the largest bore, and has always been used with PB (I don't know what that taxi reference is about). The heavier the car, the more crucial the bore size toward pedal effort. A 67-70 A-body could probably use the same bore for both PB and MB, but a heavier car will show excessive pedal effort if the bore is too big.
Edit - that chart is showing where a particular MC was used, bu tit doesn't mean that it's the only MC used for that car - 67-69 C-body is an example of that, a 67-68 could have 1 of 2 bore sizes for MB or PB.
Posted By: DoctorDiff
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/01/14 07:38 PM
A 1 1/8" bore master cylinder was never installed on a factory equipped disc brake A,B or E-body.
All else being equal, a smaller bore master cylinder will yield higher line pressure at the caliper, with a longer, lighter pedal stroke.
Posted By: DAYCLONA
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/01/14 08:26 PM
Quote:
A 1 1/8" bore master cylinder was never installed on a factory equipped disc brake A,B or E-body.
Posted By: nd65
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/01/14 08:55 PM
The description of your issue sounds like using the brakes on a power brake car with the engine not running.
You ever (with engine off) popped a PB in neutral and let it roll a bit then hit the brakes. Is that what you are describing?
You running a PB MC W/O a booster?
I would put in a correct MC for your application. I used a 1974 "A" body manual disc brake MC on my '65. Works fine.
Posted By: DoctorDiff
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/01/14 09:08 PM
The OP does not have power brakes. The factory installed 1 1/32" bore master cylinders on cars equipped with manual disc brakes.
http://www.ebay.com/itm/Brake-Master-Cyl...p=mtr#vi-ilComp
Posted By: Stanton
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/01/14 10:55 PM
Quote:
I would put in a correct MC for your application
Where's the fun in that ?!?!
Posted By: markz528
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/01/14 11:25 PM
I have the same problem with my 67 Coronet. Have the 10 inch rotors and an adjustable proportioning valve and the DoctorDiff smaller (15/16"?) master cylinder. I have the Raybestos semi-metallic pads and 10 x 2 1/2 inch rear brakes.
It just doesn't have any braking power. Last year my daughter spun the car out at the track because the rear brakes locked up.
I am going to replace the calipers with the larger 76 Volare calipers. Not sure what else to do, but right now the brakes stink!
Posted By: Kern Dog
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/01/14 11:35 PM
Awhile back when I was trying to make a manual 4 wheel disc setup work in my car, I tried a 15/16" M/C from Dr Diff. It didn't help. Nothing did and I tried several combinations of parts. I had different pads, front calipers, DRUM brake combination valves, DISC/DRUM proportioning valves, different master cylinders of various bore sizes...I took a humiliating defeat and put the power brakes stuff back on with a 4 wheel DRUM combination block and now it all works great.
This stuff can make you pull your hair out when the combination is out of whack. It really helps to have an engineered "system" instead of trying to save money by picking and choosing individual parts (AND hoping that they play well together.)
Posted By: markz528
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/01/14 11:40 PM
Quote:
Awhile back when I was trying to make a manual 4 wheel disc setup work in my car, I tried a 15/16" M/C from Dr Diff. It didn't help. Nothing did and I tried several combinations of parts. I had different pads, front calipers, DRUM brake combination valves, DISC/DRUM proportioning valves, different master cylinders of various bore sizes...I took a humiliating defeat and put the power brakes stuff back on with a 4 wheel DRUM combination block and now it all works great.
This stuff can make you pull your hair out when the combination is out of whack. It really helps to have an engineered "system" instead of trying to save money by picking and choosing individual parts (AND hoping that they play well together.)
That's not encouraging.............. 
Posted By: Mattax
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/01/14 11:50 PM
Quote:
Mike,
I've seen that chart before but don't know where it came from. It may have some errors. Here's what I found for Master Cylinder bores from Chrysler factory info (which may have errors too, but at least its from a good primary source).
The chart you posted indicates 1968-69 B-bodies used master cylinder p/n 2883058.
Chrysler's Master Technician Booklet from 1969 agrees, (Master Cylinders for 1969 model year)
However the Plymouth 1968 Service Manual shows the following specifications.
All models with Drums 1"
Kelsey Hayes equiped 1"
Bendix equiped 1"
Budd equiped 1 1/8"
That noted, the Master Technician's booklet from '67 states the Bendix equiped cars have master cylinders with 1-1/8" bores. page 13, Master Cyliner Information Are they both right? Is one wrong? Maybe, I don't know. Probably some more digging, and searching with the restoration crew would be needed.
Quote:
These are often called the "Texas" valve for obvious reasons. They are the ones I mentioned from a 73-76 A body.
Frank - wrong link/picture. Those are later combo valves. The Texas shaped valves look much more like the state! :LOL:
Quote:
I know a combination valve is in order but will that fix the feel of the brakes?
It will not fix the problem you describe. Get whatever E-berg recommended. If he recommended a proportioning valve, then just get one and plumb it into the rear line. A proportioning valve reduces the increase in hydraulic pressure to the rear wheel cylinders once the system pressure reaches a set point. For example, if the set point is 300 psi, then from 0 to 300 psi all four brakes receive the same hydraulic pressure. On a harder stop from higher speed, lets say you apply more force on the brake pedal, and the pressure from the master cylinder produced is 400 psi. If the proportioning valve is set up for 50% reduction, the front brakes will get 400 psi and the rear wheel cylinders will see only 350 psi.
Quote:
I guess I need a residual pressure valve in the rear lines as well - will that fix the pedal height?
Many master cylinders come with a the residual valve on the front port (for the rear brakes). If there is no residual valve, the springs on the shoes will squeeze alot of the fluid out of the wheel cylinderss and back into the master's resevoir.
Quote:
Brakes are bled I guess - no spongy but low and hard as hell pedal.
Read MTSC booklets on brakes to see Chrysler's recommendations on bleeding. Gravity was Chrysler's prefered method for the front discs. If you hae any doubts get a helper and do the drums with the pump shut method, and make sure the bleeders are open at least a half turn.
Quote:
Brakes just suck - low but hard pedal and I gotta stand on it to stop the car..
As others have said, could be a number of things. Troubleshoot possible faults before changing parts. A few points that may be helpful
* Recognize that duo-servo drum brakes are self energizing. They require less pedal effort than equivalent disks (unless the lining's overheat and lose friction which doesn't happen in everyday driving).
* Lining material can make a difference. Some linings have more initial bite than others. Some of the modern high performance oriented linings may say 'street' but don't really bite until warmed up. Also, many of the newer high performance linings require bedding in that transfers material from the pad to the disk (or drum). This is what AndyF was talking about. On old school and some current organic and semi-metalic linings this is not really an issue, but on many of the new performance linings, it is. Finally, any grease, oil, etc, will mess up a lining quick! Brake cleaner is your friend!
* Final thought, make sure the rear drums are adjusted properly - just a few clicks shy of dragging. At lower speeds they a contribute a lot and will effect the initial pedal feel for sure.
Posted By: cudaman1969
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/01/14 11:59 PM
Accell makes a pressure gauge that splices into the line,got one,came off a 90s pro stocker. They used it to set the line lock at a certain pressure to bump into the lights without rolling and having 3 feet. This would tell how much pressure is going to front or back. One more thing if you are using that brass splitter valve(from a previous pic)make sure the plunger is centered again,it could block off pressure to either front or back, what it was designed to do in the first place. Dodge sent me to school on brakes back in the 60s if your wondering.
Posted By: Mattax
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/02/14 12:25 AM
Quote:
Quote:
I would put in a correct MC for your application
Where's the fun in that ?!?!
He's probably close - The thing is, and what each hot rodder needs to figure out for their specific situation, is how much the brake system's balance has been altered. This is when it's worth getting a good book (like Carrol Smith or Fred Puhn's Brake Handbook) and going over scenario on paper.
For example, lets look at someone swapping front calipers. Lets ignore the disk diameter and just look at hydraulics. A stock '69 B-body would have come with Bendix calipers that had a total of 4, two inch diameter pistons. This equals 12.59 quare inches. Now how does that compare to the area of the calipers being changes too? How much difference in force applied from the stock system? This is the type of pencil and paper work that will reveal whether more or less master cylinder pressure may be needed to get the pad forces needed.
Back to the OP's Master Cylinder.
Hydraulic pressure = Force on piston from pushrod / Area of piston
1" piston, Area = .7854 sq inches
1 1/32 piston, Are = .8353 sq inches
1 1/8" piston, Area = .9949 sq inches
Therefore, for the same pedal force, we can see the effect of each of these on system pressure.
Lets say a gentle pedal puts 100 pounds force on all three piston sizes. The 100 pounds force in this example is at the pushrod, the foot is applying a lot less than that to the pedal. How much less depends on the pedal ratio - a number I don't have off-hand.
1" piston => 127 psi
1 1/32 piston => 120 psi
1 1/8" piston => 100 psi
You can see that changing to a 1" master cylinder from the 1 1/32 master that the OP already has, will make only a slight difference in pressure in the system for the any given foot pressure. Even if he stands on the brake pedal and puts 500 pounds into the pushrod, the difference in hydraulic pressure will be 600 vs 635 psi.
Posted By: 340duster340
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/02/14 01:15 AM
Are the front and rear lines run from the correct ports on the master?
Posted By: Stanton
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/02/14 02:02 AM
Quote:
He's probably close - The thing is, and what each hot rodder needs to figure out for their specific situation, is how much the brake system's balance has been altered. This is when it's worth getting a good book (like Carrol Smith or Fred Puhn's Brake Handbook) and going over scenario on paper.
For example, lets look at someone swapping front calipers. Lets ignore the disk diameter and just look at hydraulics. A stock '69 B-body would have come with Bendix calipers that had a total of 4, two inch diameter pistons. This equals 12.59 quare inches. Now how does that compare to the area of the calipers being changes too? How much difference in force applied from the stock system? This is the type of pencil and paper work that will reveal whether more or less master cylinder pressure may be needed to get the pad forces needed.
Back to the OP's Master Cylinder.
Hydraulic pressure = Force on piston from pushrod / Area of piston
1" piston, Area = .7854 sq inches
1 1/32 piston, Are = .8353 sq inches
1 1/8" piston, Area = .9949 sq inches
Therefore, for the same pedal force, we can see the effect of each of these on system pressure.
Lets say a gentle pedal puts 100 pounds force on all three piston sizes. The 100 pounds force in this example is at the pushrod, the foot is applying a lot less than that to the pedal. How much less depends on the pedal ratio - a number I don't have off-hand.
1" piston => 127 psi
1 1/32 piston => 120 psi
1 1/8" piston => 100 psi
You can see that changing to a 1" master cylinder from the 1 1/32 master that the OP already has, will make only a slight difference in pressure in the system for the any given foot pressure. Even if he stands on the brake pedal and puts 500 pounds into the pushrod, the difference in hydraulic pressure will be 600 vs 635 psi.
The later model calipers all have pistons that are about 2.75" diameter ('76 Cordoba), the area being roughly 6 inches ... half of the stock '69's !!
That said, using the same system but with the later calipers it would take less pedal to compress the piston BUT with less area it requires more pressure. Therefore, you'd want a smaller bore m/c which would take more pedal but be applying more pressure for the same effort.
This is all fine and dandy for disc to disc conversion but drum to disc conversions are a whole different ball of wax.
Posted By: BDW
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/02/14 02:44 AM
Quote:
Quote:
He's probably close - The thing is, and what each hot rodder needs to figure out for their specific situation, is how much the brake system's balance has been altered. This is when it's worth getting a good book (like Carrol Smith or Fred Puhn's Brake Handbook) and going over scenario on paper.
For example, lets look at someone swapping front calipers. Lets ignore the disk diameter and just look at hydraulics. A stock '69 B-body would have come with Bendix calipers that had a total of 4, two inch diameter pistons. This equals 12.59 quare inches. Now how does that compare to the area of the calipers being changes too? How much difference in force applied from the stock system? This is the type of pencil and paper work that will reveal whether more or less master cylinder pressure may be needed to get the pad forces needed.
Back to the OP's Master Cylinder.
Hydraulic pressure = Force on piston from pushrod / Area of piston
1" piston, Area = .7854 sq inches
1 1/32 piston, Are = .8353 sq inches
1 1/8" piston, Area = .9949 sq inches
Therefore, for the same pedal force, we can see the effect of each of these on system pressure.
Lets say a gentle pedal puts 100 pounds force on all three piston sizes. The 100 pounds force in this example is at the pushrod, the foot is applying a lot less than that to the pedal. How much less depends on the pedal ratio - a number I don't have off-hand.
1" piston => 127 psi
1 1/32 piston => 120 psi
1 1/8" piston => 100 psi
You can see that changing to a 1" master cylinder from the 1 1/32 master that the OP already has, will make only a slight difference in pressure in the system for the any given foot pressure. Even if he stands on the brake pedal and puts 500 pounds into the pushrod, the difference in hydraulic pressure will be 600 vs 635 psi.
The later model calipers all have pistons that are about 2.75" diameter ('76 Cordoba), the area being roughly 6 inches ... half of the stock '69's !!
That said, using the same system but with the later calipers it would take less pedal to compress the piston BUT with less area it requires more pressure. Therefore, you'd want a smaller bore m/c which would take more pedal but be applying more pressure for the same effort.
This is all fine and dandy for disc to disc conversion but drum to disc conversions are a whole different ball of wax.
That's a misconception, the 4 smaller pistons aren't 2x the single big piston.
You only use 2 of the pistons, they are pushing on each other.
4 piston Area = Pi*R^2 = 2*(3.14 x 1^2)= 6.28
Single piston = 3.14 x (2.75/2)^2 = 5.94
Less, but not 1/2 as much
Posted By: Mattax
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/02/14 03:36 AM
Whoa guys! We're mixing my first two paragraphs about how changes in calipers etc can effect a system (side topic) with the rest of my post about the possibility that the bore of the OP's master cylinder could be the cause of his problems. All the bore diameters listed in the second part of my post refer specifically to the pistons in the Master Cylinders.
As far as the calipers go, I do agree that IF we were going to be considering a swap from a 4 piston Bendix caliper to Cordoba caliper, we'ld want to consider fluid at displacement. Now as far as force goes; If the MC stayed the same and the amount of force applied to the brake pedal stayed the same, the pressure applied to the front brakes would stay the same, athough there would be less pedal travel.
Then at the calipers, we have to reverse the calculation to figure the force applied to the pads.
The force on one pad using Bendix calipers is 6.3 sq. in. x Pressure.
The force on one pad using a Cordoba caliper with a piston of 6 sq. in x Pressure.
Not quite the same, but in the same ballpark. At say 500 psi the Bendix would be applying 3150 pounds force and the Cordoba pad would be getting 3000 pounds force.
A more complete braking force comparison should also consider effective radius and swept area...
I also agree that drum to disk is a very different animal to calculate and fortunately we don't need to do that here!
Posted By: plazomat
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/02/14 04:33 AM
We're on to something with this (clarification). I would buy a pair of brass inverted flare male fittings to cap the MC & if it is good (& bled out) the pedal will be rock hard with virtually NO travel. Those "Edelman" fittings are cheap & you will reuse em. How about we get the MC cleared away as the culprit (I think it is guilty). It ain't the pads. with my (earlier mentioned) dart that is somewhat similar to your conversion there is a very slight bit of pedal travel & it's rock hard. EDIT If you have a MC fitting/line pigtail handy you might flatten the line end & install it in the disc port & see if the pedal is now rock hard/virtually no travel. OP post what it ends up being cuz we got bets on this one
I just ordered up the fittings to block off M/C ports and will start there - also getting a residual pressure valve cause my M/C don't have em and not sure if my wheel cyls have the right springs.
it snowed today up here..so not sure how much I will get done before the car cover goes on til spring..
Thanks for all the help - will post any findings.
Plaz
Posted By: RapidRobert
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/02/14 07:22 AM
Quote:
it snowed today up here..so not sure how much I will get done before the car cover goes on til spring.
Dont even think of puttin her to bed for the winter without finding (& sharing) what it was 
Posted By: Mattax
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/02/14 02:58 PM
Quote:
it snowed today up here..so not sure how much I will get done before the car cover goes on til spring..
Some good winter reading here about brakes and a lot more .
Enjoy.
Posted By: dragon slayer
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/03/14 02:09 AM
Quote:
A 1 1/8" bore master cylinder was never installed on a factory equipped disc brake A,B or E-body.
All else being equal, a smaller bore master cylinder will yield higher line pressure at the caliper, with a longer, lighter pedal stroke.
I think this is wrong. The Bendix Disc Master Cylinder with Booster is a 1 and 1/8" piston.
I have a 70 B body with Bendix Booster, Bendix 1 1/8" MC, KH 2.75 calipers with stock B body rotors. The rear is a dana 60 which retained 11" drums. I have the 3 piece KH dist, proportioner and meter valve. My car brakes fine. When I switched to new rotors and was breaking in the new 11" rotors I could lock up the front wheels. This was with older pads.
Lots of folks have given wrong info in these post. We just converted a 70RR to a 73up 11" big bearing rotor set up with manual disc MC. So it can work.
I would make sure your brakes are bleed correctly, no collapsed hoses, use a MC with a residual valve for the rear and no residual valve for the front. It should be a Disc manual MC for your car otherwise the rod throw can be different which effects how the MC piston moves. Even with out Meter valve for front and proportioner for rear the brakes should work, just easier to lock up rear first.
The front meter valve (hold off valve) actually holds off front application until the rears start to gripe to prevent front locking up and spinning car when roads are slick/wet.
I think the MC is the issues based on what has been stated so far. G
Posted By: QuickDodge
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/03/14 04:44 AM
I would test the brakes on a dirt or gravel road to make certain all four wheels will lock up. It may be the brakes on only one axle are working.
Posted By: Kern Dog
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/03/14 05:16 AM
Quote:
I would test the brakes on a dirt or gravel road to make certain all four wheels will lock up. It may be the brakes on only one axle are working.
Good point.
When I was neck deep in my brake fiasco, MOST of the combinations wouldn't even allow me to skid on the dirt/gravel in my backyard!
Posted By: DoctorDiff
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/03/14 06:02 AM
Once again, the OP has manual brakes. A 1 1/8" bore master cylinder was ONLY installed on POWER disc brake cars. Manual disc brake cars were equipped with no larger than 1 1/32" bore master cylinders.
Posted By: RapidRobert
Re: Disc o tech - blues....my 4 wheel drums were better. - 11/03/14 04:32 PM
Plaaaaaaz
. It ain't snowing that much up there
Posted By: plazomat
Re: Disc o tech - blues....my 4 wheel drums were better. - 07/22/15 02:27 AM
Ok digging up an oldie here but just gettin around to this.
I am try to start at the top with troubleshooting before I put in a generic disk/drum hold off/prop valve and a residual pressure valve in the rear circuit.
I have the master cyl no lines attached but with both ports plugged. The pedal is pretty firm right after the pedal free play is used up. BUT if I push hard enough the pedal seems to sink a bit - I then stop pushing cause I don't wanna bust anything.
Is this normal? Do I need to bleed the master further or is it just a bad master?
Doh - looked hard again and it seems that one of the plugs in the front port was leaking a bit sinking the pedal. Once I gave the fitting a good tightening leak stopped and the pedal held high and hard.
Will get valve mounted and plumbed next and move on from there.
Thanks
Plaz
PLAZ
Posted By: plazomat
Re: Disc o tech - blues....my 4 wheel drums were better. - 09/19/15 02:02 AM
Another update - got the generic disk/drum hold off/prop valve and a residual pressure valve installed...
It stops way way better - I still can't lock up the tires at 30-40 mph but it stops hard and straight now..
Thanks all for helping..
PLAZ