As long as I’ve had my 68 (8 years now), it’s had a small leak somewhere in the rear brake system that required me to top off the fluid in the master cylinder once every two or three months. Nothing appeared to be leaking and the brakes worked fine so long as I didn’t let it run completely out of fluid. The problem didn’t affect the front brakes at all- that part of the master cylinder has always remained full. Recently, however, things changed. Drops of fluid began appearing on the garage floor. The rear brake bowl in the master cylinder started going dry almost weekly. Well I think I’ve finally discovered the culprit-- a small cylinder shaped thingy hidden very well beneath the distribution block, further buried under all the vacuum lines. It, and the area of the inner apron below it, are soaked with fresh fluid. I believe this is the proportioning valve for the rear brakes. Am I correct? If so, I think I’ll go ahead and get an adjustable valve to replace it, but I thought I’d run this by the wise folks here first.
yes it is.they have rebuild kits to fix this.I did mine while I changed over my master cylinder.followed the video from WCCC and it was a breeze.
Terry
I have the same problem. I have the kit sitting in my step dads garage just waiting for a time to go rebuild the proportioning valve and distribution block.
Thanks. Does anyone know off hand what size the fittings are on the lines that connect to the valve? I want to temporarily stick in a coupler in place of the valve while I wait for its replacement to arrive. I realize that I’ll have too much brake bias to the rear, but that’s better than fluid leaking all over the place.
The bottom prop valve flare nut is 7/16" and the top one is 3/8".
Thanks, Bob. This should get me by for a few days. I’ll just have to remember not to stomp on the brakes too hard. If my next post is in the bodywork section, you’ll know what happened.
Ouch!
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Man, that proportioning valve was a beast to get out! I suppose I could have simplified things by taking the master cylinder off, but I didn’t want to have to go through all that. Try as I might, I was not able to crack either line on the valve loose, nor was I able to get the line on the top of the distribution block loose before rounding the fitting off to the point my flare wrench was useless. The area was too tight for even my smallest vice grip. Frustration and rage finally got the better of me so I reached for the big sidecutters, snipped off the brake lines, and used a 6 point deep socket to remove the fittings. To serve as a temporary fix, I looped a short piece of brake line between the ports, bypassing the valve.
On disassembling the valve, I found multiple issues, any one of which could have caused the leak: first and most obviously, the spring is in two pieces. Second, the small o-ring is broken, but I believe the real culprit is that the lower IF fitting is damaged- most likely from overtightening at some point. It’s hard to see in the pic, but the center cone-shaped part of the flare is nearly flattened and looks to be off center. Unlike the top fitting, however, the lower one is part of the valve body itself so I fear the whole valve may be toast unless I can think of a way to fix it. What do you guys think about screwing an adapter fitting into the damaged end and soldering it to seal it up?
" Frustration and rage finally got the better of me " 
That’s the way most brake line work ends up for me as well…
That would be under high pressure when the brakes are applied. I don’t think relying on soder to hold would be the best idea.
Yeah, you’re probably right, but I can’t foresee catastrophic failure. The worst case scenario would be that it would simply start leaking again. Another option might be to track down whatever cutter, bit or tool is used to machine these flares and use that to clean up the smashed parts.
Yeah, you’re probably right, but I can’t foresee catastrophic failure. The worst case scenario would be that it would simply start leaking again
Yes, I agree.
Jody,
Check Dorman at your favorite parts place (I use Advance), they make replacement “cigar” valves.
Edit: Maybe “no cigar” (pun intended), looks like they only have Chebbie:
http://www.dormanproducts.com/gsearch.aspx?type=keyword&q=proportioning+valve
Maybe you could look at the apps and pick the one similar to a Cougar in size/weight?
Hope this helps.
Bob