Rear Proportioning Valve.

J

jthomps3

New member
I would like to install a rear adjustable brake proportioning valve on my '83 GTI and I 'm not sure how to plumb the valve. It only has one "in" and one "out" port and I'm curious as to how other people have installed similar valves and not screwed up the front/rear side to side split. Any advise would be greatly appreciated.
 
I've seen people put a 'tee' in front of the proportioning valve to reduce to one line and a 'tee' after the valve to go back to two lines to the rear. But if one of the lines should fail then you no longer have a dual braking system (since both circuits are feeding the proportioning valve). I've also seen two proportioning valves used, one in each rear line. This is probably the safest in the event of a brake line failure as you still have the dual braking system intact.

My solution on the ITC Scirocco was to cap off one of the rear lines at the master cylinder, ran the other rear line to the proportioning valve, and used a 'tee' after the valve to the rear brakes. In *theory* this will make one of the front brakes actuate slightly sooner than the other (since that circuit also has to displace fluid for the rear brakes) but I haven't experience any ill effects of this setup. And should one brake line fail, I'll still have at least one brake circuit operational.

Mark Coffin
#14 ITC VW Scirocco - 2001 SARRC Champ (for sale)
#14 GP VW SCirocco
 
My first thought was to do what you have done, plug one rear port on the MC and run the other to the proportioning valve, but if you some how lost a rear brake you would lose both, and, since I believe most front wheel drive cars have a side to side split, you would lose the front brake on the same circuit as the unplugged rear, leaving you with one front brake. Do these A1 VW's have a front / rear side to side split?

My other thought was to run both front brakes off one end of the MC and the rears off the other (plugging one port) and create a front / rear split. Has anyone tried that?

P.S. Thanks for the info.

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ITB-GTI #31
 
If you put both fronts on one circuit (been there, done that) you'll find that you won't have enough fluid displacement to operate the front brakes, especially when the pads wear a little bit. The pedal goes to the floor. NOT a comforting feeling. I even had the unfortunate situation of running out of pedal travel (hitting the physical stop in the master cylinder) and still not slowing down. Doh! I did a quick calculation and realized that the master cylinder diameter is too small to run both front calipers off of one circuit.

You are right, that in my setup if one rear brake goes, both go and you'll be stuck with only one front brake. Not a good situation, but even with the stock system you'd still only have one front and one rear (diagonal opposite). The rears don't do that much and I suspect that it wouldn't help you much in that situation anyway!
eek.gif


Mark

[This message has been edited by racer14itc (edited December 10, 2001).]
 
I was going to install a Tilton prop. valve. I have experienced some rear lock up, mostly on downhill / off-camber situations.

I've also heard of people putting the 16V rear disc prop. valves in their cars to limit rear lock-up. Has anyone found this to work?

I didn't think about the MC not having enough volume to drive both front brakes. I think I'd rather risk being stuck with just one front brake than lose the pedal all together. Thanks for sharing your experiences.

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ITB-GTI #31
 
I run my GTI with the stock proportioning valve. All i've done is replace the load sensing spring with a turnbuckle from the hardware store. by keeping it lubricated I can change brake bias by reaching under the rocker panel and turn it by hand. Obviously ,I can't change on the fly, but I suppose it wouldn't take much to mount the valve inside the car or even run a rod or cable to the turnbuckle for adjustment. A lumbar cable from a wrecked seat would suffice.
 
Been there. First attempt was to install 2 bias adjusters, 1 in each of the rear lines. Worked good until pushed extremly hard, then I had a tendancy to lock the right front wheel. Second attempt, I pluged 1 rear port at the master cylinder. The remaining rear line went through the bias adjuster. Both front circuits piped to the front ports on the master cylinder. Then turn it all the way up unless you've got some sort of race pad on the back. Semi-metalic's won't lock up.
Works great!
Mark
 
Find a prop valve from Stainless Steel Brakes Corp. They are 1/2 the price of a Tilton. Many of the other guys use SSB prop valves with their stickers on the knob.

Here's a pic...
propvalv.jpg


- Bildon
 
Originally posted by jthomps3:
I was going to install a Tilton prop. valve. I have experienced some rear lock up, mostly on downhill / off-camber situations.

I've also heard of people putting the 16V rear disc prop. valves in their cars to limit rear lock-up. Has anyone found this to work?

I didn't think about the MC not having enough volume to drive both front brakes. I think I'd rather risk being stuck with just one front brake than lose the pedal all together. Thanks for sharing your experiences.
Click to expand...


I suspect the lockup you're talking about is the unweighted rear wheel. And while I agree that losing the brakes is a scarry situation, so is having the car hook a hard left or hard right (and possibly spin) because only one front brake is grabbing.

I like the turnbuckle idea, but I'm not sure if it's legal. Creative idea though. Need to think about that one.


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MARRS #25 ITB Rabbit GTI
 
Bill,
I never thought about the legality of a turnbuckle instead of the stock spring, but you can't run the spring anyway. As you lower the car the proportioning valve will start biasing braking rearward because it "sees" the car being loaded, which is the original purpose of the device. Besides ,if I can put in Tilton valves, braided lines ,etc., why couldn't I modify the existing hardware? I've assumed that the mod has been legal for 4 years now!
 
there is nothing that will work as well or as fast as the factory prop. valve. the key is to loosen the arm on the valve so that the amount your car is lowered or the weight you have removed is compensated for. it took a day of fooling with the tension on the arm at Summit Point Raceway to get ours set up right but the results are well worth it.
 
I run a screw type valve in my Golf. I T'd the 2 rear lines at close to the MC then ran one line to the prop valve, then I T'd the single output to a double and ran them to the rear brakes. Seems to work jsut fine.

I know lots of folks that run the stock prop valve with the arm disconnected. It's your choice, but I do like to have the ability to change the bias if there's a track change (rain!).

Good Luck!

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Colin Harmer
ITB #2 Red Golf
Halifax, NS
http://users.andara.com/~mountain
[email protected]
 
We run an A-2 golf with drums on rear ,using the stock set up.It is quite adjustable with the pinch bolt that holds one end of the spring,on the axel end.We have found that almost any needed range of adjustment is available,as long as you are aware that changing ride height at the rear does change bias adjustment.Have it marked in gradients to make quick adjustments easier.[and repeatable]
Total cost $0.00 Factory knows best!!
 
Just remember you are adjusting a knee point to allow two straight lines to follow the "ideal brake curve".

I talked with a bosch friend who designed two or three of these things (stock valve) for cars. The stock one will work, but it is very hard to get the same resolution that a dial type will have.

I bit the bullet and we plumbed all new lines for both cars with the a screw type. Mark is correct in the *theory* but we have no ill effects either. I also like being able to change for the rain, while on the track.
 
Originally posted by Dead Skunk:
Bill,
I never thought about the legality of a turnbuckle instead of the stock spring, but you can't run the spring anyway. As you lower the car the proportioning valve will start biasing braking rearward because it "sees" the car being loaded, which is the original purpose of the device. Besides ,if I can put in Tilton valves, braided lines ,etc., why couldn't I modify the existing hardware? I've assumed that the mod has been legal for 4 years now!
Click to expand...

I know from lowering my Jetta and later my Golf that Neuspeed sells a replacement bushing for the spring attached to the factory prop valve. The bushing is designed to accomodate a lowered suspension while sllowing the valve to proportion the rear brakes as stock.

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James Altemus
Nor'easter
 
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