Dead brake proportioning valve. Replacement options?

[kieferwabbit]

Hi guys,

The brake proportioing valve on my 1980 'vert recently starting leaking. I have to add fluid to the reservior every couple of days, but that's no kind of permanent solution.

It's covered in rust, and none of the fittings budge when I attempt to loosen or tighten them, so I've decided not to do anything more until I can figure out how to approach fixing.

Two different places quoted me $190 for a remanufactured valve, but that's all the money I have to spend on the entire project. Funds are tight at the moment

I saw in the service manual that the valve is connecting the RF to LR and LF to RR, and the circuits do not cross, but they come together at this valve because it attaches to the torsion beam and adjusts the pressure based on the load on the rear suspension. Makes sense, I guess. Less load = less pressure = less likely to lock up. Unless I'm seriously misunderstanding something.

Anyway, while it'd be a bummer to lose that function, could I replace the one 4-port valve with two manually-adjustable 2-port valves, so long as I keep the curcuits original? The rear brakes seem to do almost nothing when it comes to stopping, so I'd probably set the bias heavily forward and forget about it.

Does that plan sound feasible?

[CalAltaDubber]

After reading your post, I consulted my Bently. I am making an assumption that the braking system is simular to that in my two cars ('87 and '88), so I can be wrong.

My Bently says that there are two proportioning valves mounted on the master cylinder, and they limit the hydraulic pressure applied to the rear brakes.

The proportining valves are NOT adjustable. I can't tell if they are seperate parts from the Master Cylinder, but the Bently only instructs to remove them as part of the master cylinder.

In any event, it means you have to remove the lines from them. Since you state the connections are rusted , you will need to liberally spray the connections with something like PB Blaster, Liquid Wrench or something like that. Give them a good doucing, and let them sit for a few hours , then spray them again an let them sit for a few more hours. Then try to break the lines open. Just try not to crimp the brake lines.

You might check your local wrecker for a master cylinder with the proporting valves attached.

Hope this helps.

[Briano1234]

The Cabriolets have 2 proportional valves. They are attached to the master cylinder at the front left and right rear.


They are usually 2 separate cylinders.

On earlier rabbits, there was a proportional block on the drivers side inner fender, but that was 80-82 and not specifically Cabriolets.

The valves themselves usually don't leak, as they are a diaphragm I have taken them off and shot brake cleaner through them. I suspect that the seals are the culprit
and not the valves themselves.

To take them off, you have to have a 11mm brake line wrench and remove the upper brake line off of the valve.
First clean the brake line with a little sand paper to get all the crud off, and free the line, I usually go up about a inch.

What happens is that the crud will bind the nut and twist the brake line, and twist it enough and it will break.

ONLY USE A BRAKE LINE WRENCH TO PREVENT STRIPPING THE NUT.... IF YOU STRIP THE NUT, then you might have to use a pair of vice grips and a hammer.

Soak the Nuts on the top with pb-blaster for about 30 minutes.
Place the brake line wrench on the nut and try to turn...If it is tough, then try to smack the wrench with a hammer.

You may have to shield things and apply a little heat. I would bet your master cylinder is shot....
Once you get the brake line off, then you can detach the proportional valve with a 15mm at the base I think....Not sure on the size.

[CalAltaDubber]

Gee Brian,

Seems I was headed in the right direction with this, but you have provided much better information.

[Briano1234]

Gee Brian,

Seems I was headed in the right direction with this, but you have provided much better information.

No worries, what with the mods that folks can do, it may be that a one piece was inserted instead of the two separate.
The issue then would be stopping power.

The whole purpose of the valve is to prevent the back brakes from locking up by limiting the fluid pressure and qty to the rear wheel cylinders.

[kieferwabbit]

Okay, the piece I am talking about is at the back of the vehicle, but I feel like you guys are talking about something in the engine compartment.

This is mounted next to the rear axle. Four lines go to it. One to each rear brake, then two head forward, and I didn't trace them.

I took this photo of it:

[Briano1234]

Yes we were but we have never seen once of those, as that is the difference between a German built of that year and a american built rabbit.

Chances are is that you have a line leaking and that you may want to get to a wrecking yard and find a newer style cabriolet and upgrade.

[CalAltaDubber]

OK, you have given me a little more information to work with here.

I have a Haynes manual that covers older models. Based on your description and picture, here is what I found in the Haynes:

"To prevent rear wheel lockup, these vehicles are equipped with a proportioning valve located in the engine compartment at the master cylinder and a brake pressure regulator which is bolted to the chassis and connected to the rear axle by a spring-loaded lever."

Is this it?


It appears that your car is equipped with the pressure regulator. It turns out '80 to '84 models are equipped this way.

The big problem here is, the Haynes doesn't say any more about it.

Base on the picture, it sure looks like it is the pressure regulator that is leaking.

I found one at German Auto Parts, http://www.germanautoparts.com/Volkswag ... rake/235/5 for $155.63. Thats a bit cheaper than what you were quoted.

You might start checking your local auto wreckers for one.

I wish I could provide more info for you.

[Briano1234]

Had a similar set up when I converted my 92 caravan to vacuum brakes from electrical/hydraulic. The rear leaf spring had a proportional valve srm on it where I had to replace the entire leaf spring to get that arm.

As it is weight actuated, I would think you could place a 90s master and master Proportional valves on your car as a good retro-fit and get rid of all that....

I would seriously try to get a brass brush to clean all the lines up prior to trying to get the nuts off as you don't want to be breaking the lines other wise you will be buying bulk line and bending and fitting.

My 81 Diesel had the valve on the inner fender drivers side....

[kieferwabbit]

Is this it?


...

I found one at German Auto Parts, http://www.germanautoparts.com/Volkswag ... rake/235/5 for $155.63. Thats a bit cheaper than what you were quoted.

You might start checking your local auto wreckers for one....

Yes, that looks like a clean version of the valve in question. I was not aware of that site -- that will definitely save me some cash. Since this appears to be a German-only part, checking the local yards might not yield much usable fruit. I'll probably just buy a new one and suck up the cost. And the Bentley, which I have, does have a little information on it, luckily.

And Briano, I really am not prepared to retrofit this car with a newer braking setup. If I can replace the valve and get the system working as designed without paying through the nose, I will.

Also, I absolutely don't want to be replacing any lines, so I will be getting the old valve as clean as humanly possible, then soaking it down in blaster before attempting removal.

I understand there's a special wrench for the brake lines. Any more info on that?

[Briano1234]

They are called Brake Line Wrenches. They look like a standard box end wrench, but they have a slot it one side to go over the brake lines.

[CalAltaDubber]

Yes, that looks like a clean version of the valve in question. I was not aware of that site -- that will definitely save me some cash. Since this appears to be a German-only part, checking the local yards might not yield much usable fruit. I'll probably just buy a new one and suck up the cost. And the Bentley, which I have, does have a little information on it, luckily.

German Auto Parts is an American company that specializes in German/European cars. I've never ordered from them, but I do know several who have. They seem very satisfied with the service.

I'm not sure what you mean by German only part, since it appears that all '80 to '84 cars were equipped this way. I think it's more of a case of vintage. your car bieng older, makes the part a little harder to find.

[Briano1234]

I have ordered lots of stuff from Germanautoparts, they send what you order.
My 81 Diesel which was a Westy built (USA), had the proportional valve to the left of the master as you look at it on the inner fender as I said.
I would think that this is a German built Cabby, and as such they did it for weight control. This is similar to the 92 caravan that I had. The more weight on the springs the proportional valve opened up to allow greater pressure to the rear wheel cylinders.

I would strongly urge you to replace the rear wheel cylinders if you haven't don't it lately as the increase pressure of the fluid on a working unit may blow the seals out of them too.

[CalAltaDubber]

I would strongly urge you to replace the rear wheel cylinders if you haven't don't it lately as the increase pressure of the fluid on a working unit may blow the seals out of them too.

That's a good point Brian, I totally agree.

[kieferwabbit]

Thanks for all of the help, guys. Now I just have to wait for the weather to warm up. There's over a foot of snow on the ground now here in KC, and it's still coming down!