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Rear brake proportioning valve

13K views 37 replies 13 participants last post by  bluetoes591 
#1 ·
So we were working on the race car today (engine swap went well, car runs great now), and while underneath we found this valve near the driver side rear to be leaking from right around the middle where this rubber band is around it. It was a very tiny kinda weeping leak.

Our problem is I am trying to find this part and NOBODY has it (not partsgeek, not germanautoparts, the local place that honestly could get a water pump for a Tucker but can't get this), any suggestions?
 
#3 ·
Well we like how the rear brakes behave as is, so it would be preferable to just keep whats stock as opposed to put something adjustable in that we have to mess with to get where we want it. Bypassing it could cause them to lock too easily when threshold braking, we definitely don't want that.

I just hope this part exists in someones warehouse somewhere.
 
#8 · (Edited)
...

I went as fas as trying to find a NEW pair of these in Brazil, with no success..., you should consider buying adjustable aftermarket to resolve the issue at once, or hope you can get a used pair that its still usable...many aren't- seem them at junk yards - all showing sign of leakage...good luck!
 
#9 · (Edited)
I went as fas as trying to find a NEW pair of these in Brazil, with no success..., you should consider buying adjustable aftermarket to resolve the issue at once, or hope you can get a used pair that its still usable...many aren't- seem them at junk yards - all showing sign of leakage...good luck!
This is bad news.... I have some searches going on out there but no luck so far. I was thinking maybe theres a way I can repair the one on there, maybe somehow seal the hole its weeping from. Are you familiar with this part? It seems like there is like a rubber band in a groove around the middle and its weeping from under that.

Any idea what pressure needs to be held to the rear brakes, maybe these would work:

http://www.wilwood.com/MasterCylinders/MasterCylinderValves.aspx

Scroll down to Residual Pressure Valve, theres a red one and a blue one red is 10lb blue is 2lb. Both say they are for rear drums. Or do I need one of those ones with the knobs and I kinda just have to guess at where it should be (not a fan of this)
 
#11 ·
Just tried it, thats not it :-( That looks like it runs all the brakes, the valve I'm looking for looks kinda like this except 1 side is male:



It mounts just above the rear axle.
 
#12 ·
Ok, so you have a sedan. sorry. Find one in a junk yard.

You can also take the valve out of the system. Change your brake line from two lines going to the rear from the master to one line with a splitter. You don't need both. It is a safety system, in case one brake has a leak, the other side will still work.

If you change it to one line and eliminate the valves in the rear, you can put the adjustable proportioning valve under the hood near the master. You set it in the middle, and then adjust from there. You set it so the rears lock up. Then adjust until the fronts lock up just before the rears.

This is what I did on a Datsun truck 30 years ago. Same exact thing. Change two line to the rear, to one with a splitter.

I also have a adjustable proportioning valve on the 914. It is under the car replacing the orginal.

Not that hard to set up. Once you have this on your car, you can adjust to your liking.

Greg W.
 
#13 ·
Thanks for the tips, I may have to just do that and make the whole custom setup if I must.

I really just wish I could find a stock replacement though and be done with it as the brakes work perfect as is (we have 16v Scirocco brakes up front with hawk blues, they work as good as the Brembo 4 pots on my Camaro thanks to the light weight of the car, rear brakes are just stock pads/drums but we only need light braking back there, its perfect). Been emailing people parting foxes out on here but no luck so far. Worst part is I had a parts Fox last year but didn't think to even save these parts. Local yards don't have Foxes, I've tried....
 
#14 · (Edited)
Ok so my friend found this:

http://www.autopartswarehouse.com/d...ortioning_ValveQQ19851992QQW0133-1609765.html

These LOOK like what I need but they are for a Golf, this site has no listing other than racing adjustable valves for the Fox. I'm getting desperate at this point

EDIT: Called the local dealer asked them to check/cross reference and they said there is no cross reference for the part from the Fox to this Golf part. I'm leaning toward just taking the risk.....
 
#16 ·
Ordered them, with new lines.... praying for the best. Even if the pressure is reduced a bit more than factory on a Fox, I'm fine with that, we don't need the rear brakes to be strong. Plus this will be a good fix for everyone else! if it works
 
#20 ·
i think parts palace had the wagon rear proportioning valve
not that I was specifically looking for it, but no place I looked had this one either, I know its significantly different right?
 
#21 ·
So I got these:

http://www.autopartswarehouse.com/d...ortioning_ValveQQ19851992QQW0133-1609765.html

And some new brake hoses during the week.

I installed them and they DO WORK. The only thing to know is they are a little tight fit because they are slightly longer than the old ones, but its not hard to get them in there. The rear brakes seem to work identically, and they do NOT lock up before the fronts so I would say these are definitely good enough especially for street driving. I have another race in a couple weeks so we will see if they cause any issues there.
 
#26 ·
Somewhere on the internets, there was someone who had rebuilt the inline Fox sedan proportioning valves. I took a bad one apart aside from an o-ring or two, the tricky part seemed to be finding a correct sized replacement for the small spring seal. It also seemed that finding and using a small enough hone without taking off too much material from the cylinder would be an issue.

For replacements I used some junkyard scores. It took two sets before I found some that didn't leak. Other VW cars with rear drum brakes had the same or similar valves but at the master cylinder instead of under the car. There are similar valves for cars with rear disc brakes but they're not interchangeable (wrong activation pressure).

It's too bad there aren't pre-fab replacement seals for these or for the wagon valve you're talking about, SourKandi. It would make it much easier to deal with these as they rust out.
 
#29 ·
Somewhere on the internets, there was someone who had rebuilt the inline Fox sedan proportioning valves. I took a bad one apart aside from an o-ring or two, the tricky part seemed to be finding a correct sized replacement for the small spring seal.
I'm thinking of rebuilding the original valve with seals and o-rings from another similar vw brake prop valve e.g. golf, jetta or fox wagon. Would that even be possible?
 
#28 ·
Here's the link that at least shows what's inside. Maybe I'm wrong in remembering the spring seal, but i think it's the one directly under the valve in the picture.

Someone here once talked about deleting the prop valves and running rear brakes on a single circuit. Since the valves are installed to keep the rear from locking up under hard braking and since I wasn't comfortable doing that, I actually ran my car with leaky valves for years. When I installed the replacements, I realized my rear brakes probably weren't even doing any braking during that time.

The other option seemed to be finding a valve with similar activation pressure but then the question would be the fitting sizes. Doable, but perhaps difficult. I just don't know enough about the tolerances of the system to do much other than plug and play replacement parts.
 
#30 ·
You could find a VW with a similar brake set up. As an example, some of the MKII Jettas came with a solid front rotors and drum rear brakes. One of these prop valves may be close enough to use. Just a thought.

Greg W.
 
#31 ·
I replaced the stock wagon propportioning valve with some in-line parts off of a rear drum mk2 golf. No problems at all.
 
#34 ·
Does anybody have the brake proportioning valve from a coupe/sedan out of the car? Does it have any markings on it at all? I know what the VW of America part number is, but I suspect this does not appear on the part, but maybe something else does? Not an uncommon type of part in Brazil but there are so many different ones.
 
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