Weak Rear Brakes?
Thread Starter
Racer
Joined: Apr 2006
Posts: 322
Likes: 0
From: Rockford MI
Weak Rear Brakes?
Hello all, I am suspecting a problem with my rear brakes. I am thinking they may not be as strong as they should be. I have the car on jack stands and was running the car in gear and found the rear brakes won't hold the tires from turning with anything more than a high idle.
I have confirmed the calipers are functioning properly and the Pistons not siezed up and also bleed the brakes hoping that may be the problem.
I'm wondering if the proportioning valve could be stuck or something wrong with the master cylinder? Although it is not leaking. The front brakes are solid, as I've been driving the car not realizing the rears are marginal.
Has anyone rebuilt a proportioning valve?
Any ideas would be appreciated. Thanks
I have confirmed the calipers are functioning properly and the Pistons not siezed up and also bleed the brakes hoping that may be the problem.
I'm wondering if the proportioning valve could be stuck or something wrong with the master cylinder? Although it is not leaking. The front brakes are solid, as I've been driving the car not realizing the rears are marginal.
Has anyone rebuilt a proportioning valve?
Any ideas would be appreciated. Thanks
Advanced
Joined: Oct 2014
Posts: 68
Likes: 3
Hello all, I am suspecting a problem with my rear brakes. I am thinking they may not be as strong as they should be. I have the car on jack stands and was running the car in gear and found the rear brakes won't hold the tires from turning with anything more than a high idle.
I have confirmed the calipers are functioning properly and the Pistons not siezed up and also bleed the brakes hoping that may be the problem.
I'm wondering if the proportioning valve could be stuck or something wrong with the master cylinder? Although it is not leaking. The front brakes are solid, as I've been driving the car not realizing the rears are marginal.
Has anyone rebuilt a proportioning valve?
Any ideas would be appreciated. Thanks
I have confirmed the calipers are functioning properly and the Pistons not siezed up and also bleed the brakes hoping that may be the problem.
I'm wondering if the proportioning valve could be stuck or something wrong with the master cylinder? Although it is not leaking. The front brakes are solid, as I've been driving the car not realizing the rears are marginal.
Has anyone rebuilt a proportioning valve?
Any ideas would be appreciated. Thanks
...First gear rear wheels should be pretty tough for your car to stop with floating tires and no power brakes.
2026 Loser of the Year
Joined: Sep 2013
Posts: 36,600
Likes: 7,046
From: New Or-leens Loo-z-anna
I had to replace the flexible rubber hoses on my rear brakes...they were nearly swollen shut internally not allowing the pistons to push as hard as they should against the pads/rotors.
Thread Starter
Racer
Joined: Apr 2006
Posts: 322
Likes: 0
From: Rockford MI
Thread Starter
Racer
Joined: Apr 2006
Posts: 322
Likes: 0
From: Rockford MI
Le Mans Master
Joined: Oct 2007
Posts: 7,455
Likes: 977
From: RI, Now Franklin/Nashville TN
Bleed the rear brakes….
If the brakes cannot hold the car at anything above idle, there is a problem. Corvette brakes with 4 piston calipers have tremendous clamping force.
If the brakes cannot hold the car at anything above idle, there is a problem. Corvette brakes with 4 piston calipers have tremendous clamping force.
Thread Starter
Racer
Joined: Apr 2006
Posts: 322
Likes: 0
From: Rockford MI
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Safety Car
Joined: Mar 2007
Posts: 3,652
Likes: 49
From: Bridgewater nj
The proportion valve gets stuck if the pedal is forced down fast while bleeding sometimes. This is how to unstick it.
Force the pads back by pushing the piston in on both calipers. Use a piece of wood to hold the pads in place, all the while watching the master cylinder for overflow.
Then top off the master if need be and remove the wood. Now this is very important, do not let the master run dry, donot press the pedal to the floor and use short very slow strokes to pump the pedal back to normal. Then crack the bleeder screw and watch for bubbles. No pumping needed.
Force the pads back by pushing the piston in on both calipers. Use a piece of wood to hold the pads in place, all the while watching the master cylinder for overflow.
Then top off the master if need be and remove the wood. Now this is very important, do not let the master run dry, donot press the pedal to the floor and use short very slow strokes to pump the pedal back to normal. Then crack the bleeder screw and watch for bubbles. No pumping needed.
Le Mans Master
Joined: Sep 2003
Posts: 8,812
Likes: 2,029
From: eastern NC
Hello all, I am suspecting a problem with my rear brakes. I am thinking they may not be as strong as they should be. I have the car on jack stands and was running the car in gear and found the rear brakes won't hold the tires from turning with anything more than a high idle.
...Any ideas would be appreciated. Thanks
...Any ideas would be appreciated. Thanks
Good luck... GUSTO
Drifting
Joined: Apr 2008
Posts: 1,305
Likes: 2
From: Lewisburg WV
thegazman
Could be the master cylinder or brake proportioning/distribution valve. The valve on my 79 was stuck because of crude. If that's the problem the brake light will be on. If you do install a new master cylinder be sure and bleed the brakes on all four wheels until you completely flush the system. Also purchase a center tool for the valve prior for this type of bleeding. I went through the same problem and wound up replacing the M/C and the proportioning/distribution valve. Great brakes all the way around now and all my fluid is fresh.
Thread Starter
Racer
Joined: Apr 2006
Posts: 322
Likes: 0
From: Rockford MI
The only other things is that the brake pedal seems lower than i would like. Again, hard to tell if it is normal or not.
Drifting
Joined: Apr 2008
Posts: 1,305
Likes: 2
From: Lewisburg WV
thegazman
The car seems to stop fine, ive never tried to panic stop with it. Im now doubting it would lock up the rears in a panic situation. Whether it should or not i dont know, but it seems like it should.
The only other things is that the brake pedal seems lower than i would like. Again, hard to tell if it is normal or not.
The only other things is that the brake pedal seems lower than i would like. Again, hard to tell if it is normal or not.
Le Mans Master
Joined: Oct 2007
Posts: 7,455
Likes: 977
From: RI, Now Franklin/Nashville TN
I think that the 2 likely culprits is either air in the system-the gazman procedure should identify an air issue-or the stuck brake proportioning valve.
The C3 brakes are very different and way superior to all the other GM cars from the 60/70/80's with a 4 piston fixed racing caliper up front and the same 4 piston fixed racing caliper in the rear with 12 inch vented discs front AND rear. The only difference between the front caliper and the rear caliper is that the pistons on the rear caliper are slightly smaller..slightly. The C3's also have much better front anti dive behavior than almost every car back then, primarily due to the superior weight distribution on the SB C3's which are slightly rear weight biased with years like my 78 being 48%F/52% rear which is why I suspect GM added the rear proportioning valve to the system. I can share that with my 78 under severe heavy braking, the fronts will lock first, and with continued brake pedal pressure, the rears will also lock. Like most well balanced rear wheel drive cars even today, the brake split would be about 60% front and 40% rear…these cars are NOT FWD vehicles with 90% of the braking being done by the front calipers/rotors.
The C3 brakes are very different and way superior to all the other GM cars from the 60/70/80's with a 4 piston fixed racing caliper up front and the same 4 piston fixed racing caliper in the rear with 12 inch vented discs front AND rear. The only difference between the front caliper and the rear caliper is that the pistons on the rear caliper are slightly smaller..slightly. The C3's also have much better front anti dive behavior than almost every car back then, primarily due to the superior weight distribution on the SB C3's which are slightly rear weight biased with years like my 78 being 48%F/52% rear which is why I suspect GM added the rear proportioning valve to the system. I can share that with my 78 under severe heavy braking, the fronts will lock first, and with continued brake pedal pressure, the rears will also lock. Like most well balanced rear wheel drive cars even today, the brake split would be about 60% front and 40% rear…these cars are NOT FWD vehicles with 90% of the braking being done by the front calipers/rotors.