Front brakes dragging
Burning Brakes
Joined: May 2008
Posts: 1,116
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From: Middleburg Florida
what you've done is validated that pressure is "trapped" in the caliper. Since the master cylinder is what sends that pressure to the system, it's a good place to start. Mikes suggestion of loosening the mounting bolts is spot on. It'll tell you if the master is returning to the static position or not. If not, the problem is in the master. If the master is returning, there's likely a caliper issue.
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Ok, I will put pressure back in the system and crack loose the nuts that hold the MC to firewall to see if it frees up the fronts. If so, the maybe the rod/pedal assm. does not have enough slack? As, Dannys8 stated above, the front wheels will not turn any farther than I move them. Any chance of the proportioning valve playing a role in this?
Le Mans Master
Joined: Aug 2010
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I've been reading VB&P's tech, their o-ring seals shouldnt cause the symptoms you are having, if I confused any one , I am sorry, my experience comes from years...and years of fixing other folks mistakes. The best answer still is to call VP&P but they are closed till monday, the 2nd best would be another member who installed VB&P, had the same issue and fixed it., hope this helps. if... your other parts worked fine prior to changing the parts, they should work fine now, you shouldnt throw parts at a problem in the hopes that
'something ' works.
'something ' works.
Race Director
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It's very simple. If the relief ports in the M/C are not fully uncovered when the pedal is released, pressure can be trapped in the lines holding BOTH brakes locked or dragging. The most common cause for the relief ports not being uncovered is either the m/c piston is sticking or the pushrod/mc combo is incorrect not allowing the piston to return.
Ok, I will put pressure back in the system and crack loose the nuts that hold the MC to firewall to see if it frees up the fronts. If so, the maybe the rod/pedal assm. does not have enough slack? As, Dannys8 stated above, the front wheels will not turn any farther than I move them. Any chance of the proportioning valve playing a role in this?
Le Mans Master
Joined: Aug 2010
Posts: 9,272
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Ok, I will put pressure back in the system and crack loose the nuts that hold the MC to firewall to see if it frees up the fronts. If so, the maybe the rod/pedal assm. does not have enough slack? As, Dannys8 stated above, the front wheels will not turn any farther than I move them. Any chance of the proportioning valve playing a role in this?
Le Mans Master
Joined: Aug 2010
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You sound like a nice guy with good intentions and all that- but not too experienced in Corvette brake systems.
It's very simple. If the relief ports in the M/C are not fully uncovered when the pedal is released, pressure can be trapped in the lines holding BOTH brakes locked or dragging. The most common cause for the relief ports not being uncovered is either the m/c piston is sticking or the pushrod/mc combo is incorrect not allowing the piston to return.
You have a '72, there is no 'proportioning valve' per se, it's a simple distribution manifold with a pressure differential switch. Very different animal. If the valve were to malfunction, the brake warning light would be on and most commonly there would be a low pedal and lack of brakes, the opposite of what you have.
It's very simple. If the relief ports in the M/C are not fully uncovered when the pedal is released, pressure can be trapped in the lines holding BOTH brakes locked or dragging. The most common cause for the relief ports not being uncovered is either the m/c piston is sticking or the pushrod/mc combo is incorrect not allowing the piston to return.
You have a '72, there is no 'proportioning valve' per se, it's a simple distribution manifold with a pressure differential switch. Very different animal. If the valve were to malfunction, the brake warning light would be on and most commonly there would be a low pedal and lack of brakes, the opposite of what you have.
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Thanks everyone, I will try some things tomorrow. The CEO (ie my wife) would prefer that I don't spend a second whole day in a row working on the mistress!! I will report back with what I find.
Mike, it is interesting to know that the "valve" is just a manifold on 72's.
Mike, it is interesting to know that the "valve" is just a manifold on 72's.
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You sound like a nice guy with good intentions and all that- but not too experienced in Corvette brake systems.
It's very simple. If the relief ports in the M/C are not fully uncovered when the pedal is released, pressure can be trapped in the lines holding BOTH brakes locked or dragging. The most common cause for the relief ports not being uncovered is either the m/c piston is sticking or the pushrod/mc combo is incorrect not allowing the piston to return.
You have a '72, there is no 'proportioning valve' per se, it's a simple distribution manifold with a pressure differential switch. Very different animal. If the valve were to malfunction, the brake warning light would be on and most commonly there would be a low pedal and lack of brakes, the opposite of what you have.
It's very simple. If the relief ports in the M/C are not fully uncovered when the pedal is released, pressure can be trapped in the lines holding BOTH brakes locked or dragging. The most common cause for the relief ports not being uncovered is either the m/c piston is sticking or the pushrod/mc combo is incorrect not allowing the piston to return.
You have a '72, there is no 'proportioning valve' per se, it's a simple distribution manifold with a pressure differential switch. Very different animal. If the valve were to malfunction, the brake warning light would be on and most commonly there would be a low pedal and lack of brakes, the opposite of what you have.
So, Mike. If I crack loose the MC and that frees up the brakes, then that would lead to the rod/adjustment being incorrect?
If I crack free the MC, and the brakes stay dragging, that would point to the MC piston sticking. Does that sound correct?
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Race Director
Joined: Jul 2001
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If not, the loosen the lines coming out of the distribution block/manifold to the fronts till the pressure bleeds off.
Instructor
Joined: Dec 2009
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the last time my front brakes were dragging it was the proportion valve.
part number 523706 at Vett Parts Plus or last detail vett parts. Cost $65 new. I would hold off on all the other stuff and check out the proportion valve next. If you replace it you need to center the piston before bleeding.
part number 523706 at Vett Parts Plus or last detail vett parts. Cost $65 new. I would hold off on all the other stuff and check out the proportion valve next. If you replace it you need to center the piston before bleeding.
Pro
Joined: Feb 2009
Posts: 651
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From: North Port Florida
Do like the one fellow recommended and loosen the nuts holding on the master cyl. Do it when the problem is occurring. This problem will be more evident when the brakes have been used, rather than cold. Good luck!!!
Drifting
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From: gold coast queensland
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OK, problem update:
I tok loose the nuts holding the MC to firewall (no PB on this vehicle), and pulled the MC out a bit. No change, front tires still very difficult to turn. Next, I took the front brake line loose from the MC, and voila! After a rotation or two, the front tires are much easier to turn (there is still resistance, but I imagine there is always some amount of friction between pads and rotor). So, is there something in the MC that is supposed to "pull back" a small amount of pressure when you let off the brakes thus pulling the caliper pistons back? If so, I guess the MC is bad?
I tok loose the nuts holding the MC to firewall (no PB on this vehicle), and pulled the MC out a bit. No change, front tires still very difficult to turn. Next, I took the front brake line loose from the MC, and voila! After a rotation or two, the front tires are much easier to turn (there is still resistance, but I imagine there is always some amount of friction between pads and rotor). So, is there something in the MC that is supposed to "pull back" a small amount of pressure when you let off the brakes thus pulling the caliper pistons back? If so, I guess the MC is bad?
Le Mans Master
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Race Director
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Two separate circuits, two separate reservoirs, two separate relief ports, two separate sets of seals on the M/C piston. The only place the two systems 'touch' is in the manifold on opposite sides of a piston. If there's not enough differential pressure and flow to push the piston aside and turn the warning light on, then the rears are not affected.
Le Mans Master
Joined: Aug 2010
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I understand your logic, but same piston, same spring, same distance traveled by the piston i'll be following this thread closely to see what the outcome is.
to the op, before you buy parts, call VB&P in the morning
to the op, before you buy parts, call VB&P in the morning
Le Mans Master
Joined: Aug 2010
Posts: 9,272
Likes: 17
I understand your logic, but same piston, same spring, same distance traveled by the piston i'll be following this thread closely to see what the outcome is.
to the op, before you buy parts, call VB&P in the morning
to the op, before you buy parts, call VB&P in the morning