Sitting in garage for 17 years. Getting it back on the road. While bleeding the brakes I can get the fronts to bleed with the pedal going to the floor. The rears seem to bleed but the brake pedal stops part way down and no amount of pushing will get it further. After finishing, with the pedal pushed, the fronts work but the rears do not. I can see the rear calipers moving, but not enough to lock to the rotors. I bought a new MC and am ready to install it but I am wondering if maybe the 'combination valve' could also be involved. This is the brass fitting down on the frame that distributes front and rear pressures. Any thoughts on this? Thanks

 

Have you replaced any parts prior to bleeding? Calipers? Hoses? It would help to know what you're starting with.

 

Have not replaced anything else. New brakes, etc installed 17 years ago however and sitting in dry storage. The MC was almost dry of fluid and the fluid was gooey and black. I am going to disassemble the MC today to see if the rear chamber is rusted. I suppose it doesn't hurt to replace the combination valve then, if I can find one.

 

New MC and proportioning valve, no love. Must be stuck rear calipers, the fronts work fine.

 

It is possible that the Brake Proportioning Valve (really just a distribution valve as proportioning is controlled by different size pistons front & rear) is locked in the fore or aft position.



The valve is designed to let you know when a leak develops on the front or rear segment of the brakes. A leak in the rear will allow the brake pressure to push the valve in position to block the rear outlet and simultaneously press the switch (in the middle of the valve) turning the brake light on. By blocking or restricting flow to the rear it prevents a massive loss of fluid.

Occasionally when bleeding the brakes it is possible for the valve to be pushed in one direction or the other because one side (front or rear) sees much greater pressure than the other. Normally the first indication is that the brake lite is now on. Is your brake lite on?

If your valve is in fact blocking the rear port, you'll need to get it to re-position itself in the center. This can sometimes be done by opening a bleeder on the opposite side (in your case the front) and with all of the rear bleeders closed build pressure in the rear by pumping the brakes. I'm sure others may have additional ways to do that and will let you know how they do it. You'll know when the valve is back in the center because the brake lite will go out.

There's also a lot of good info here also on troubleshooting the brake proportioning valve.
https://www.corvetteforum.com/forums...alve-long.html

Good luck and let us know what you discover... GUSTO

 

I replaced the MC and the proportioning valve. Still the same result. I started the car (power brakes) and stepped on the brakes and blew out three of the calipers. Replaced all four and all is good now. Thanks for your assistance.

 

Wow... I'll bet that was a mess!!!

Good to hear you've solved the problem Dave and thanks for letting us know how you did it.

Any pictures of how the "blown" calipers looked inside?

GUSTO

 

I did not take the calipers apart, just got rebuilt ones at AutoZone. No pics, sorry guys. Bit messy though.