1967 Brake Proportioning Valve Rebuild

[Len Gerstner]

I need some advice on overhauling my manual disc brake system. I was browsing through several vendor catalogs and found that they provide a rebuilding service for the proportinoing valve located directly under the master cylinder. The going rate for rebuilding my proportioning valve appears to be around $80. It appears to me that the valve body is a machined solid block of brass and accordingly can't be opened for internal servicing. Am I correct in thinking that rebuilding the proportioning valve is a waste of money? The brake system on the car works fine other than having leaky calipers. Any advice is greatly appreciated.

[Joe L.]

Re: 1967 Brake Proportioning Valve Rebuild

Len-----

Except for the 267, or so, 1967 Corvettes equipped with J-56 brakes, no 1967 Corvette was equipped with a PROPORTIONING VALVE. The "valve" of which you speak is actually just a brake system hydraulic distribution block with an integral switch to detect a front-to-rear brake system pressure imbalance. When a pressure differential is detected, indicating the partial or complete failure of one of the two systems, the pressure differential sensing switch causes the dash "BRAKE" warning light to illuminate. This is usually the same light that illuminates when the parking brake is applied. So, if it illuminates when the parking brake is off, you possibly have an hydraulic brake system problem.Not every 67+ Corvette owner knows that, though.

If your switch is working properly as far as the pressure differential function is concerned and is not leaking, it requires no service. This valve was never designed to be serviced except as an ASSEMBLY. However, the discontinuation of most of these valves by GM has created the need to develop unit servicing techniques for existing valves. If necessary, "rebuilds" are probably best left to those with experience doing it.

By the way, except for J-56 brake Corvettes NO 67 to 77 Corvette had a brake proportioning valve. Although several different part numbers were used over the 67-77 model years, ALL were simply distribution blocks with the presure differential sensing switch. In 1978, the part changed to a COMBINATION VALVE. This valve has combined proportioning, hydraulic fluid distribution, and differential pressure sensing functions. This valve was used for 78-82.

[Duke W.]

Re: 1967 Brake Proportioning Valve Rebuild

I concur with Joe. Wipe the outside of the switch block with mineral spirits to clean off any dirt and oil residue. When dry submerse it in denatured alcohol to thouroghly clean the inside of any trace of old brake fluid. Once squeaky clean, dry it thoroughly and inpect the visible interior surfaces with a magnifying glass. If there is no evidence of corrosion or contamimantion, just put it in a baggy until you're ready to install it.

Duke