Proportioning Valve

[Hawker7]

I installed all new brake components but keep the original proportioning valve. It seems to be leaking where the rear brake line fitting goes into. I don’t think it is leaking from the rear brake fitting, but from the fitting on the proportioning valve itself. It looks like the piece threads in, but it would not budge when I tried to tighten it. Has anyone else had a leak here? Anyone know if this can be tightened?

[68gmsee]

I would take another real, real close look at it. Clean out any fluid accumulation and have someone work the pedal while you check carefully. Could be a fine crack at the end of the fitting or maybe the fluid is oozing out between the threads.

Not to say that they won't leak, but personally, I have never seen a proportional valve leak.

[Hawker7]

I just doubled checked and it is leaking in front of the fitting for the rear brake line on the Proportioning Valve itself. I also looked at some pictures I took when I first got the truck and it looked wet around that same area. Has anyone else had a leak here? Does that part unscrew?

[68gmsee]

Here's a bump for you...

I know those valves are not cheap. And, brake fluid can ruin you paint. So, if it were me, I'd remove it completely from the truck and clamp it on a vise and put some torque to it. My guess is that it is a part that is not made to be removed but is removable since there's parts inside that valve.

[Hawker7]

I took the valve off, and was able to tighten it enough so now it does not leak. The problem now is the back brakes don't work at all. Everything is new except for the Proportioning Valve so I'm not sure what the problem could be. I was able to gravity bleed the lines, so I know fluid is getting back there. I also checked the pin in the valve, and it dosn't seem to be sticking out. The front brakes do seem to work though.

[68gmsee]

Do they not work at all? No movement? Some guys say to stomp on the brake a couple of times to reset the prop. Valve? You can try that.

Personally, I don't like the gravity feed method. I'm sure it works but I'm not the patient type. If you have an assistant (wife, kid brother, good friend) ask him to push on the pedal until it stiffens and then release the bleeder valve to see if fluid squirts out.

Also, if you don't have anyone to help, I would raise the rear tires, crank the truck and slowly engage the tranmission. Visually check to see if the rear wheels stop when you step on the brakes.

The front brakes should do most of the braking. The rear ones assist. Make sure they're adjusted so that you can hear or feel them lightly touch the rims when you turn it by hand.

[JCKAHK]

I just had the same thing happen on my 72 I discovered that the rear brakes where not working when I replaced the master cylinder. Took prop valve apart and cleaned it out and it just would not work. They are very expensive new. From what I found out researching on the web they are universal so I found one on a newer truck in the junkyard and it worked fine.

[Hawker7]

I did some work on this last night. I bleed the brakes again, and after some time got much better fluid flow in the back. I then took the drum off, and could see the wheel cylinder working. I think my problem now is the brakes just need adjusted. At least nothing is leaking anymore. When I first put everything together ALL my fittings leaked. I couldn't believe how tight you need to make the fittings so they don't leak. I got all new stainless lines, and I have been told they need to be real tight for them to seal since they are harder. Took my about a week of every night tighten the fittings more and more until one day I came out and nothing had leaked overnight.

[68gmsee]

Good heads up on the stainless steel lines since I've been thinking of doing the same to my 69.

[Hawker7]

Originally Posted by 68gmsee

Good heads up on the stainless steel lines since I've been thinking of doing the same to my 69.

Make sure you get a set of flare nut wrenches. There is no way I could have tightened them as tight as I did w/o them. Also, you should make sure you get a flare nut wrench that fits the couplers as well as there is a good amount of torque applied to them as you tighten the fittings, and you don't want that one to slip either. I would also suggest putting something under the fittings to protect the paint for a few days if you have redone your frame. I had some fittings that I thought were done leaking, and did not leak when I pushed the pedal, but only to come back a day later and notice that they had leaked.

[Hawker7]

Well, After a few days of no leaks my Proportioning Valve starting leaking again last night. At this point I'm about done screwing around with it and would just like to get a new one. Does anyone know where I can get a new one? I don't really want to get a used one from the parts yard.

[stope4]

did you press the button on the front of the proportion valve. Usually you have to depress it to get the valve equalized on the inside. If it were me, I'd find a used one and repalce the rubber gasket on that fitting that's leaking. You can then clean the whole thing out and experiment with how the valve works on the inside. Their not that complicated and you can replace the o'rings at the same time. Just make sure you get o'rings for brake fluid service.