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Re: Brake pressure at caliper...700 psi?
[Re: DoctorDiff]
#859026
11/28/10 12:01 PM
11/28/10 12:01 PM
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Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
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Posts: 36,041
Lincoln Nebraska
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I'm wondering if the prob is in the calipers/pads themselves or as said even something simple as a slight bit of trapped air, maybe just not enough to feel mushy
live every 24 hour block of time like it's your last day on earth
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Re: Brake pressure at caliper...700 psi?
[Re: DoctorDiff]
#859029
11/28/10 03:28 PM
11/28/10 03:28 PM
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Joined: Jul 2003
Posts: 60
Smith Mtn Lake, VA
karls67gtx
OP
member
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OP
member
Joined: Jul 2003
Posts: 60
Smith Mtn Lake, VA
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Doctor Diff,
My old MC was 15/16 also but was leaky so I decided to upgrade to yours. I am running 15" cragars with BFG 235/60s up front with stock semi metallic pads.
FuryUs,
I wouldn't say that locking up the front brakes is the problem, more about inadequate braking. (about the same as drum before) hence the troubleshooting...discovered that brake psi should be 1000-1200, I only have 700, that feels like the problem, just not enough clamping force when brakes are applied, no matter how hard the pedal is pushed.
Mopar Man
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Re: Brake pressure at caliper...700 psi?
[Re: karls67gtx]
#859030
11/28/10 11:34 PM
11/28/10 11:34 PM
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Joined: Jan 2003
Posts: 28,114
Irving, TX
feets
Senior Management
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Senior Management
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Posts: 28,114
Irving, TX
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I think you need a smaller bore on the master cylinder to go with the new brakes.
Too large of a bore on the MC will make a very stiff pedal. You went from drum to disc so the fluid capacity of the brakes changed. That's where things went sideways on you.
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
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Re: Brake pressure at caliper...700 psi?
[Re: karls67gtx]
#859031
11/29/10 12:45 AM
11/29/10 12:45 AM
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Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
70Cuda383
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Posts: 21,345
Marysville, O-H-I-O
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Quote:
I wouldn't say the pedal is hard to push, it goes down OK just have to push real hard to get a good stop. When you say drop one size, do you mean go up in size? I would love to but just purchased this new 15/16 from Dr Diff.
I know it seems counter-intuitive, but to increase line pressure, you go SMALLER on your master cylinder, or LARGER on your caliper piston.
it's a leverage thing. with a smaller diameter master cylinder, the same amount of effort you put into the system will move LESS volume, but create MORE pressure. vice versa, a larger diameter master cylinder will move a lot more fluid volume, but you won't be able to create as much pressure. it's like gears...shorter gears will not push you as far, but the leverage is much easier. taller gears will push you further per revolution, but the effort required is much higher.
so if you're having trouble generating the line pressures needed to get maximum braking effort, then drop a size or 2 in diameter of your master cylinder. if you have a 1", go to a 15/16" or a 7/8" if that's still too stiff, drop to a 3/4"
when I was converting my truck to manual brakes, I took the pedal ratio and size of the pistons in the front calipers, and calculated what size master I would need to generate 1200 psi. unfortunatly, I let the "expert" at Master Power tell me that I could never run a disc brake system on less than a 1" master, ever. so that's what I bought. my pedal effort is a little higher than I'd like it to be...but not enough to make me want to spend more money on the smaller master that I wanted.
**Photobucket sucks**
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Re: Brake pressure at caliper...700 psi?
[Re: 70Cuda383]
#859032
11/30/10 11:11 PM
11/30/10 11:11 PM
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Joined: Jul 2003
Posts: 60
Smith Mtn Lake, VA
karls67gtx
OP
member
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OP
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Joined: Jul 2003
Posts: 60
Smith Mtn Lake, VA
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Update on pressure testing, I was finally able to get to the store for an adapter to test the MC pressure....1000-1200...no problem. I am going to do some more testing but if I have 1000-1200 at the MC, shouldn't I have it at the calipers? Maybe I have some air trapped somewhere...thanks for all the help so far.
karl
Mopar Man
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Re: Brake pressure at caliper...700 psi?
[Re: karls67gtx]
#859034
12/01/10 12:17 AM
12/01/10 12:17 AM
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Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
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Posts: 36,041
Lincoln Nebraska
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Quote:
but if I have 1000-1200 at the MC, shouldn't I have it at the calipers?
yes. that only leaves a proportioning/crimped line/hose prob (somewhere intransit from M/C to caliper) or air or the calipers have a mechanical prob. Smaller bore M/C will give more psi (& you have plenty)
Last edited by RapidRobert; 12/01/10 10:37 PM.
live every 24 hour block of time like it's your last day on earth
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Re: Brake pressure at caliper...700 psi?
[Re: RapidRobert]
#859035
12/01/10 10:00 PM
12/01/10 10:00 PM
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Joined: Jul 2003
Posts: 60
Smith Mtn Lake, VA
karls67gtx
OP
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Posts: 60
Smith Mtn Lake, VA
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Pressure testing update...tested just before the rubber line on drivers side tonight, barely 700-800, which is what I am getting at both front calipers. I would like to just put a new T in for the front brakes to eliminate the distribution block. I can do this right? I have a rear adj prop valve to control pressure at the drums. I guess I am just wondering if this will be OK, don't really want to pony up the 139 for a new combo valve. thanks for all the HELP...almost there. -karl 
Mopar Man
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Re: Brake pressure at caliper...700 psi?
[Re: karls67gtx]
#859036
12/01/10 10:18 PM
12/01/10 10:18 PM
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Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
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Lincoln Nebraska
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All I can add is I put 74 A discs/10" BBP drums/large bore M/C on a 65 Dart keeping the OE 4 wheel drum splitter & no other proportioning and it stops fine w no excessive wear on the front pads. Not the way it is supposed to be done but it's an around town slow speed daily driver & I've had NO issues.
live every 24 hour block of time like it's your last day on earth
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Re: Brake pressure at caliper...700 psi?
[Re: AndyF]
#859038
12/02/10 01:38 PM
12/02/10 01:38 PM
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Joined: Feb 2004
Posts: 936
OLD318
super stock
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super stock
Joined: Feb 2004
Posts: 936
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Your low pressure at the calipers is due to 2 main factors: 1) MC bore and 2)metering valve If you switch to a small bore MC 15/16" you will have higher pressure but slightly further pedal travel If you switch to a large bore you will have less pressure but a shorter pedal distance... Ideally you want 1000psi at the calipers w/o having to leg the #### out of it! When I switched my 70 Coronet to front disk from power drum, you have to switch the metering valve to a disc brake metering valve, that and a 1" bore MC with a disc brake booster (not power drum booster - I got the MP Brakes version) I have 1000 psi w/o legging it if I really put my leg into it it goes 1200+... I tried the setup with the drum brake booster and metering valve, I couldn't get 1000psi with all the leg I could muster - max was 900psi the avg was around 750 psi... The brakes did not work very well. It stopped the car but it was not a "significant improvement" over the 10" drums.. Once I got the right metering valve the pressure went up... But it wasn't until I added the disc brake booster that I got it where I wanted it.. I'm currently looking into a rear adjustable proportioning valve (w/ guage) to dial in the rears. When I really leg it (really hard sudden stop)the rear wheels will lock and skid... I'd like to dial it down a tad in the rear and see if I can get it to just stop locking.. Oh well... yet another project...  Hope this helps - Best of luck to you!
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Re: Brake pressure at caliper...700 psi?
[Re: hooziewhatsit]
#859040
12/02/10 03:07 PM
12/02/10 03:07 PM
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Joined: Jan 2003
Posts: 28,114
Irving, TX
feets
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I went from manual 4w drums to manual 4w discs and it made an IMPRESSIVE improvement.
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
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Re: Brake pressure at caliper...700 psi?
[Re: feets]
#859041
12/02/10 04:48 PM
12/02/10 04:48 PM
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Joined: Jan 2008
Posts: 299
East Brunswick, NJ
finadk
enthusiast
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enthusiast
Joined: Jan 2008
Posts: 299
East Brunswick, NJ
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It is possible that the proportioning valve has "tripped" in other words when bleeding the brakes did it think there was a broken line to the rear shut of the pressure to the rears?
I think there is a way to reset it by really jamming on the brakes, you might want to do a google search about resetting a proportioning valve.
Good luck.scott
Scott
1956 Dodge Custom Royal Lancer (408 Stroker, 4 Wheel Disc Brakes, Rack & Pinion, 6 speed)
2002 Dodge Ram 1500 Quad Cab
1976 Corvette
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Re: Brake pressure at caliper...700 psi?
[Re: Ledman_70]
#859042
12/02/10 10:00 PM
12/02/10 10:00 PM
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Joined: Dec 2003
Posts: 23,554
Here
jcc
No soup for you!!!
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No soup for you!!!
Joined: Dec 2003
Posts: 23,554
Here
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Quote:
This may be useless info, but I recently installed a complete SSBC 11" front disc setup on my 64 Polara, including mc. I couldn't get the brakes to lock even on gravel, so I called SSBC's support line. I figured with 11" rotors and 4 piston calipers, the brakes should stand me on my nose, but the tech guy said they were designed like the original Kelsey-Hayes units Mopar used in the early 70's and were designed NOT to lock. I told him if I had known that I wouldn't have bought them. My buddy installed a 4-wheel Wilwood system on his 61 Falcon and Wilwood's tech support told him the same thing... his wouldn't lock either. I believe the thinking behind these designs is to make them anti-lock like new cars, but personally I don't like the control being taken out of my hands. My brakes stop the car ok, but not much better than the drums did, and the one time I got caught in the rain, they locked easily when I stepped on them with the same pressure I used normally. This sure seems like a poor design to me, but I'm not the best with brakes. I even bled mine with a power bleeder, but they're still mushy and I get NO air out during bleeding.
Say what? On a non abs system, the ONLY thing that PREVENTS brake lock up is your foot. Every brake system properly designed must be capable of locking up the brakes, since there are so many variables found when driving a car, weight, speed, road surface, trailers, etc
I am suprised it took so long for the downside of upping line pressure by decreasing MC diameter to be mentioned, increase in brake pedal travel, and if not careful with caliper piston sizes/numbers, lack of pedal volume. There are downsides to nearly every solution.
Did I miss anyone asking what the pad choice is, or if pads were corrrectly broken in and not glazed? 
I'm with Helmuth Hübener, and no soup is being served today.
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Re: Brake pressure at caliper...700 psi?
[Re: OLD318]
#859043
12/02/10 10:17 PM
12/02/10 10:17 PM
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Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
Challenger 1
Too Many Posts
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Too Many Posts
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Posts: 28,312
Cincinnati, Ohio
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Quote:
I'm currently looking into a rear adjustable proportioning valve (w/ guage) to dial in the rears. When I really leg it (really hard sudden stop)the rear wheels will lock and skid...
I'd like to dial it down a tad in the rear and see if I can get it to just stop locking..
Oh well... yet another project...
Hope this helps - Best of luck to you!
Sorry to get off topic, OP. I already posted above to try to help.
Yes there is alot to gained with a rear brake proportionong valve. I have one plumbed into both my cars and can balance the front to rear and it does make a huge difference. 4 tires gripping the same is awesome.
I mounted the one on my 74 under the dash, I can adjust it while driving and it makes a huge difference in braking these old Mopars.
You can mine in this picture, it's the MP valve, took some creative tubing work. 
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Re: Brake pressure at caliper...700 psi?
[Re: Challenger 1]
#859044
12/02/10 11:19 PM
12/02/10 11:19 PM
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Joined: Jan 2003
Posts: 6,816
Alton, IL
Dakota_Don
master
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master
Joined: Jan 2003
Posts: 6,816
Alton, IL
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try this, test the psi at the calipers,then remove the P valve on the front.. connect the front with a fitting to bypass the valve, then see what kinda PSI you have at the calipers.. that should tell you if the valve is bad, or whatever.. maybe it will narrow it down..if you have 1000 psi, with the valve removed then you found the problem,
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Re: Brake pressure at caliper...700 psi?---SOLVED
[Re: Dakota_Don]
#859045
12/11/10 07:54 PM
12/11/10 07:54 PM
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Joined: Jul 2003
Posts: 60
Smith Mtn Lake, VA
karls67gtx
OP
member
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OP
member
Joined: Jul 2003
Posts: 60
Smith Mtn Lake, VA
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Finally got some time to wrench on the brakes. I bought a simple T for the front brakes to bypass the distribution block. Put a couple of new fittings and bam...1000 psi at the calipers, 1100 on the second push. Drove it and could not believe the difference!  It stops with the same amount of effort in a new car with power brakes. I don't know why the old distro block would not push the 1000 psi but I will have to investigate further when the weather warms up. thanks for all the help!! karl
Mopar Man
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