damoroso

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.

72 corvette roadster

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?

oldalaskaman

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.

Mike Ward

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.

oldalaskaman

its a chance, if it were stuck, but that usually means only the front or rear brakes work. have someone apply the brakes and see if the rear brakes spin freely

oldalaskaman

I pick on you cause you always have good tech. hard to get it out of you sometimes, many thanks, bob

72 corvette roadster

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.

72 corvette roadster

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?

Mike Ward

Pretty much yup. If it still sticks with the M/C nuts backed off, loosen the line for the front brakes (put a cloth underneath to catch fluid drips). If the both front wheels are now easy to turn that confirms it's the M/C.

If not, the loosen the lines coming out of the distribution block/manifold to the fronts till the pressure bleeds off.

69ttop

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.

kh400

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!!!

DANNYS8

Did'nt mean to cut in with my question,Sorry for that but can anyone answer my question about my brakes or do I need to start a different post.Again sorry for that

gingerbreadman1977

Your asking the same thing as the the original thread starter asked in this post so why dont you just read along??

72 corvette roadster

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?

Mike Ward

Sticking piston in the M/C. There is a spring that should push the piston back to it's rear stop at which time the relief ports are uncovered and the line pressure reduces to zero.

72 corvette roadster

Ok, thank you everyone. Looks like I need to replace the MC. Any suggestions on where to purchase a QUALITY replacement?

oldalaskaman

why arent his rear brakes dragging also if there's not a proportioning valve?

Mike Ward

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.

oldalaskaman

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

oldalaskaman

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