1976 corvette brakes

[mcgahgl]

I have had this vehicle for several years and it always has bad bakes. I recently decided to attack this problem. I replaced all calipers, master cypinder and pwerbooster combo and bled system. I had no pedal. I took it to the local shop where they said that one of the calipers was bad (reman). They replaced left front, then they replaced master cylinder again, then then right front caliper, then the lines, power bled the system and STILL no pedal. If they pinch off a line, they get full pedal, once they release a line, we lose pedal. Any suggestions? Glen

 

[Hib Halverson]

When they "pinch off a line" and they get pedal, which line are they pinching?

 

[mcgahgl]

The front lines, the rear have no change. Thats why we changed out the calipers again, thinking they were the problem. I wonder if the porportion valve would cause this?

 

[Toms007]

mcgahgl, I'd like to welcome you to CAC. I am also going to move this thread to the C3 Technical, where it will receive the correct audience and you will more apt get responses.

 

[GTR1999]

First off C3 brakes can be setup safely and work for many thousands of miles.
Are you losing the pedal after drving or at bleeding? If you bench bled the master and it's the correct one, that should be good. The valve is nothing but a spool that shifts during pressure loss, if you loose the front brakes the spool shifts and the dash parking light comes on to "warn" you.

If you have a motive bleeder, install it and pump it up to 10-12 psi. Do one circuit at a time. Watch the gauge with the system closed,it should not drop. If it does you have a leak and will have to trace it.

If you are loosing the pedal after driving you probably have rotor runout pumping air into the system. The runout should not be more then 005 although I set all mine work to under 003" The endplay in the bearings should also be under 003, I set mine to 0015-002"

Lastly some caliper rebuilders are not so good. There is a place in FL that moves and changes thier name because of the lousy work they do and terrible business practices they have. The ss calipers a lot sell are done by Lone star and I haven't had a problem with those. If done correctly and tested they should not be a concern.

 

[JohnZ]

If there are no fluid leaks anywhere and you can't get a firm pedal, you either still have air in the system or the fluid is bypassing the piston seals in the master cylinder.

 

[jp1]

The front lines, the rear have no change. Thats why we changed out the calipers again, thinking they were the problem. I wonder if the porportion valve would cause this?

The rubber brake hoses as they age and break down expand when pressure is applied to them. This will cause a soft brake pedal. I highly recommend changing your brake hoses at the front. You should also do your rears due to the age. Do this before you throw any more parts at the car.

 

[Copdogcorvettes]

The rubber brake hoses as they age and break down expand when pressure is applied to them. This will cause a soft brake pedal. I highly recommend changing your brake hoses at the front. You should also do your rears due to the age. Do this before you throw any more parts at the car.

Replace all the rubber flex lines.. Not only can they leak they can suck air back into the system. Another problem they cuase is collasping inside and locking pressure on that caliber. If you haven't replaced them DO IT. They don't cost much and can solve a lot of different problems.

Gary

 

[92BlackVette]

My 76 needed the following brake lines replaced: front crossovers, front rubber lines, rear SS lines, and master cylinder before the petal would get firm.

 

[jetset0045]

I've heard of the same problem on a newer car that someone had changed brakes on...they had let the caliper hang from the rubber line while changing the pads....this caused the rubber line to collapse inside and had similar symptoms as your problem...i'd bet a rubber line has collapsed inside.....just my 2 cents...

 

[BOB SWEETING]

Brake problem

It is rarely the rubber hoses. GM put on several million of them. A low pedal is either because of loose wheel bearings, or the caliper pistons are pulling back due to improper positioning of the boot on the piston. IF that is good, I.E. NO clearance between the caliper piston and the pad, The Hydroboost power brake system is REALLY the answer. It has incredible power and the pedal rod is adjustable. Many times the pedal is really close to the floor because of the think floor mats. See POWERBRAKESONLINE.COM