Rear Proportioning Valve Options

[BenNC]

I've seen a few posts that mention replacing the proportioning valve for the rear brakes with a "tee".

1. Is it safe?

2. Is it street legal?

3. Is it useful if I'm retaining the stock brakes?

4. What is involved besides simply replacing the valve with the tee?

Thanks,

Ben

[airsix]

I've seen a few posts that mention replacing the proportioning valve for the rear brakes with a "tee".
1.  Is it safe?

Depends.

2.  Is it street legal?

Who cares? (IMG:style_emoticons/default/happy11.gif)

3.  Is it useful if I'm retaining the stock brakes?

Questionable. You'll have firmer pedal feel but brakes might not be balanced correctly.

4.  What is involved besides simply replacing the valve with the tee?

Not sure how hard it is to get the lines to all come together at the 'T'. I use a $40 adjustable Willwood proportioning valve instead. Firmer pedal AND proper bias. Best of both worlds.

-(the other) Ben

[BenNC]

Thanks "other" Ben (what are the chances that two Bens have consecutive member numbers?)

BTW: Beautiful bird! How in the world do you find the time? I can barely keep up with a dog.

I hope the brakes don't become and issue once I get the go installed, but its good to know what the alternatives are.

[echocanyons]

did the willwood have the same size fittings as Porsche?

[jonwatts]

What keeps the knob from turning by itself? Friction? Detents?

This is the kind of thing that will kill my budget. I have a "T" from a bug that I bought at a swap meet for $2.50, but at $40 the Wilwood is reasonable (even tho it costs over 150% more).

[airsix]

What keeps the knob from turning by itself? Friction? Detents?

This is the kind of thing that will kill my budget. I have a "T" from a bug that I bought at a swap meet for $2.50, but at $40 the Wilwood is reasonable (even tho it costs over 150% more).

He he he. No Jon, your buying $800 worth of quarter panels as an impulse buy is what will kill your budget! (IMG:style_emoticons/default/smile.gif)

The Wilwood valve doesn't have metric bubble flare fittings - you'll have to get adapters at a bug shop.

I can't remember if the knob has detents or if it is just stiff. Anyway, there's no concern about it backing out on it's own.

[jonwatts]

He he he. No Jon, your buying $800 worth of quarter panels as an impulse buy is what will kill your budget! (IMG:style_emoticons/default/smile.gif)

It felt like an impulse buy but I think it was a matter of seeing them on a blue race car at Brad's shop that did it for me. It's been my desire all along to build something that was my own and I'm having a blast doing it, but seeing that red V8 car in Modesto go for $7500 on Ebay the other day made me think a bit.

Eh, live and learn.

[cha914]

I just put a vw T in place of the rear prop valve and the hardest part was getting the old prop valve out...puttin the T in was no problem at all, the lines are easy to get into place.

I also put a adj prop valve in the passenger compartment right in front of the firewall...that was more of a pain...as I had to cut and reflare the lines. It would have been easy if I had more than 6 square inches of work space...anyway, I would not recommend putting it in this location unless you like to cut and bang a good bit (IMG:style_emoticons/default/smash.gif)

however, it will be fun to play with the brake bias at the first autox (IMG:style_emoticons/default/tongue.gif)

- Tony

[Don Wohlfarth]

Why are you removing proportioning valve? The valve reduces pressure to the rear brakes. You usually want a bias something around 60-65 front as that's where the majority of the braking takes place. No experience but I've heard of removing valve completely with no ill effects (but don't think I'd do it.)
If you remove valve completely or install adjustable valve bleed the brakes. Test the brakes. Take a friend out on a deserted road/large parking lot. One drives, the other watches driver come to a hard, fast stop from 50-60mph (without locking brakes and flat spotting tires (IMG:style_emoticons/default/wink.gif) ). The one outside the car is looking to see if you lock rear wheels.
You want to be able to barely lock rear wheels on hard stop 2 out of 3 times. When you get there (and it's harder than it sounds) you have too much rear brake. With adjustable valve reduce the pressure to rear and try again until you cannot lock rear wheels.
If you have removed the valve and installed a tee and lock rear wheels, reinstall the old valve. Do not drive your car if you can lock rear brakes as it will spin you in a heart beat when you least expect it. (IMG:style_emoticons/default/cool_shades.gif)
Just starting out, I would think your time would be better spent making sure that all your brakes are working correctly, decent pads, calipers not dragging, if unsure last time rubber brake lines changed replace them, and thoroughly flush brake system once or twice.
Adjusting the brake bias from the cockpit sounds cool. In reality, even with adjustable valve it's a set and forget deal. If you're constantly fiddlin' with the brake bias while driving the car you should park it and try and figure out what's wrong.

[Sammy]

the tee is usually installed after a front brake upgrade like the BMW calipers. After that kind of a change the bias is all messed up, so removing the prop valve "may" correct it.
I do not recommend removing the prop valve with completely stock brakes.
The tee fits just fine, no real bending or modifications necessary.

BTW, for the street, the back brakes should not lock up in a panic stop in a straight line on dry pavement.
if it's set up that way the car will achieve better stopping results, but it will also make the car less safe in the hands of a novice.
many times a panic stop is attempted in a corner, or the driver trys to turn and panic brake at the same time. If the back brakes are locking up, guess what happens? the car turns into a maytag.
So, the safe way would be for the rear brakes to not be able to lock up unless traction is limited.

Having said all that, most of the people here would have no problem with more rear brakes than normal, but "this aint your ordinary party crowd. there are professionals here"
Name that movie (IMG:style_emoticons/default/smile.gif)

[cha914]

Adjusting the brake bias from the cockpit sounds cool. In reality, even with adjustable valve it's a set and forget deal. If you're constantly fiddlin' with the brake bias while driving the car you should park it and try and figure out what's wrong.

I realize this and I will mark the adj valve when I finally get it dialed in ... but for that initial dial in period I didn't want to be crawling under the car every time I had to make an adjustment...

I pulled out the old valve cause I didn't trust it wasn't holding air in it and I wanted the adjustability...

Tony

[airsix]

Why are you removing proportioning valve? The valve reduces pressure to the rear brakes. You usually want a bias something around 60-65 front as that's where the majority of the braking takes place.
(snip)
Adjusting the brake bias from the cockpit sounds cool. In reality, even with adjustable valve it's a set and forget deal.
(more snip)

I agree that in most instances you need a proportioning valve of some kind, unless the brake caliper/rotor/pad combination is perfectly balanced front/rear. In reality that's not likely especially if you've tinkered with the brakes like me (911 vented A's on all four corners). Enter the adjustable prop valve to adjust away any minor errors in your design.

As for the "set and forget" comment, I'll agree for a street car (or in my case a street/autox car), but for a serious racer I can see the need for adjustability on a frequent basis. Brake bias optimization is a function of weight transfer, and weight transfer is a function of available traction. If less traction is available on a given day there will be less weight transfer and hence a need for more bias to the rear brakes - for optimal braking ability that is. So, you would use a different bias on different surfaces, when using different tires, or rain vs. dry. This is picking nits and I agree that for a street car you should just set and forget.

ps- The modern adjustable valves give a much firmer pedal than the stock valve. The stock valve is a flaming piece of dog doo. (IMHO) The stock valve is a big contributor to the mushy brake feel of the stock brakes.

[Brad Roberts]

This is what I have found in OUR cars.

I install brake bias:

Customer drives car..adjust...adjust....adjust.... and end up with it WIDE open which would amount to a 2.50 tee. Our local PCA region doesnt allow you to mount the bias inside the car. I personally install the tee and adjust with different brake pad compounds (aggressive fronts and stock rears) or vice versa.

The only way (I feel) to get good brake bias adjustment is to run twin master cylinders with a balance bar like true race cars do (like mine)

Its not really something we are constantly adjusting. You set it where it makes you comfortable and worry about winning.

B

[BenNC]

OK, so how do I decide if my proportioning valve is in need of replacement (other than the obvious "Now how did that tree end up in the front trunk?")?

[cha914]

Brad...any idea why they don't allow a bias mounted in the car? Also, when you have done this in the past are you usually running stock brakes or a car with upgraded brakes?

BenNC...as far as I know the best way to tell is when you bleed, bleed, bleed and you still feel like you have air in your brake lines...its usually the stock prop valve that is the problem.

Tony

[jdogg]

Hey BENNC - I guess that since you are asking about the proportioning valve, you must not have your motor in yet?!?! You better get cracking, Laurinburg AX is only 4 weeks away!!!!!!!!!!!!

[Brad Roberts]

Tony,

They dont want us adjusting them while on the track or AutoX course.

These are 4cyl cars with stock calipers/braided lines/19mm MC. Sticky tires/Porterfield R4S pads or R4.

I have tested and tested with the tee and with Wilwood adjustable. I have also tested running 4 front calipers on the car (stock front calipers on the rear and stock fronts on the front) This saves some headache with ordering pads and I dont need a E-brake for our street/race cars.

B

[campbellcj]

Hey Brad, I've gotta disagree with ya on this one.

My tee cost about $8, not $2.50. LOL.

Maybe that's just LA prices (new VW OE part, at at Bug shop).

Works well. New 19mm m/c, new rotors, SS lines, no e-brake. I need some more aggressive pads up front though; I think the A calipers have a street pad (OEM flavor) in them and the 914 fronts in the rear have Pagid Oranges.

[cha914]

well thats nearly what my car has... stock calipers, braided lines, 19mc, (sticky tires are on the way), and I am running pagid oranges up front and metal masters in the rear, so well see how this works out...

[BenNC]

(IMG:style_emoticons/default/biggrin.gif) Yeah jdogg you might still end up being the fastest 914 in Laurinburg. I keep falling victim to a combination of time and "while I've got ________ off I should go ahead and _________"

Hopefully the Opel will be campaigning this year, but the options for tow vehicles is getting slim.