Proportioning valve

[L48]

The proportioning valve on my 75 appears to be leaking. On the bottom there is a small hole that was sealed with a small check ball, and it it leaking from there. Anyone else have this problem?

Also any input on how much a new one should cost would be appreciated. I guess I could rebuild it if that option is available. I found a brass one on Corvette Central for $83, I just wonder if that is my only option.

I would prefer one that looks like the stock valve unless it costs twice as much.

 

[WayneLBurnham]

Yep...when I changed mine (and rebuilt the calipers)

FINALLY my brakes got tolerable. I always suspected that thing!

BTW, it's just a BALL of fun getting all five of those snaked lines reattached! Absolutely get a set of good crow's feet "sockets" and a good set of line wrenchs and get real comfortable under that thing - it'll take effort to loosen them and a lot of patience to get them all started on the new one. If you try to use regular wrenchs or something else, you will nuke the fittings and be cast into the nether hells. Hose that thing down in brake cleaner, WD-40, pentrating oil, holy water - whatever - for a while before you tackle it.

My old one was brass too, albeit blackened from years under the car - I assumed they all were. Paint it if it bothers you - or try one of those brass black products which deposit the black sulfide or oxide or whatever that is when brass blackens. (Possibly vinegar blackens it too - I can't remember.)

 

[L48]

Wayne - thanks for the reply. Turns out it is quite timely.

Today I was under the car working on the brakes. I was able loosen (and subsequently retighten) all the lines that connect to the proportioning valve with some line wrenches and a 7/8 end wrench to hold that large fitting that goes into the back of the proportioning valve itself. I did not remove them yet - just wanted to see if the brake lines would come free or if any of them would also need replaced.

While investigating I noticed the wire to the sensor on the proportioning valve was off. It took a while but I found the connector. When I hooked it up to see if the brake light in the car would come on, I lost power to everything - no brake lights, wipers, radio, nothing! After about 5 seconds I realized I was probably dealing with a grounding situation, and located a grounding strap between the frame and the body on the driver side not far from the proportioning valve. (I know its fiberglass but part undereath is metal). I removed the strap and cleaned the connections. After reinstalling everything was back to normal with the addition of a functioning "brake" light in the dash.

I'll look for the brass blackener you are describing - thats a good tip. And I am going to scratch on the old one to see if it is brass - sounds like it will be.

I am debating the idea of bleeding it at least once to convince myself I need to shell out $ for the replacement part.

 

[L48]

Update:

Decided to just bleed the brakes. First a gravity bleed then assistance from someone pumping the brakes and holding down the pedal while I opened the bleeders one at a time. Pedal was nice and solid after that.

After test drives found the master cylinder was leaking at the back. Replaced the cylinder. Jury is still out on the proportioning valve.

 

[joe1975]

I had a 74 once that the valve had a crack in it the brakes would lock up soild while I was driving to where the car would not move and I would have to wait about a hour for them to bleed down, took a while to find that problem

 

[KANE]

Update:

Decided to just bleed the brakes. First a gravity bleed then assistance from someone pumping the brakes and holding down the pedal while I opened the bleeders one at a time. Pedal was nice and solid after that.

After test drives found the master cylinder was leaking at the back. Replaced the cylinder. Jury is still out on the proportioning valve.

Don't forget about hairline cracks in the lines heading to the rear of the car. I replaced a proportioning valve on a 78 I had. It drove me NUTS. I don't envy you and I will include you in my prayers (for having to pull all four wheels and possibly the valve). Ugh.

 

[Chuck-75]

:ugh I replaced the valve on my old 77, and what a messssssssss had brake fluid running up my arm, and ended up laying in a puddle of brake fluid while trying to get all the lines reinstalled.NOT A FUN job to do but really glad I got it done. I didnt have any leaks just the brake light was staying on. I cant remember correctly !but was told to check if the valve is working ,pull the wire and see if the light goes out on the dash? (Mine was staying on). and this was a way to determine that this was my problem . Save the wave

 

[L48]

Don't forget about hairline cracks in the lines heading to the rear of the car.

This is a good point - thanks. I have seen cracks in tranny lines before (in the seat area near the nut where it is secured to the radiator) but hadn't thought of this.

:ugh I replaced the valve on my old 77, and what a messssssssss had brake fluid running up my arm, and ended up laying in a puddle of brake fluid while trying to get all the lines reinstalled.

Maybe I will take the lines out of the master cylinder and plug the master cylinder to minimize the mess. Probably would not have thought of it without the warning - thanks. I had a similar situation when I was fixing the gas line, with gas running down the arm and a big mess on the floor.