Proportioning Valve, Stock, adjustable, or Tee Options

[ventedrib]

I have 911front suspention with A calipers stock 914 4 calipers rear should I use stock proportioning valve an adjustable one or a tee.

[SLITS]

Use the stock one if you can bleed the air out of it.

[70Sixter]

With those front calipers I would think a T would be adequate. The adjustable would be my next choice, especially if you track the car.

[maf914]

You may want to do a search for proportioning valve. Some good threads. Some of the explanations may answer your question. It sure made me wonder about using that adjustable prop valve I bought and have in my parts stash.

[sww914]

What are you doing with the car?
A lot of racing you'll want an adjustable valve.
No racing and bigger front calipers with stock rears your balance should be about right with a tee.

[Heeltoe914]

What are you doing with the car?
A lot of racing you'll want an adjustable valve.
No racing and bigger front calipers with stock rears your balance should be about right with a tee.

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[Dr Evil]

Never use a T. Where is Eric Shea?..... T is old folk tale that has proven dangerous.

[jmill]

I fought this one out on the other site. I raced for years and used a proportioning valve. I liked the rears to lockup shortly after the fronts. That way I knew I had maximum breaking in the rear. The adjustable valve let me tailor my braking for the conditions and my choice of tire. I don't care if your on the track or on the street great brakes save you and others from damage and injury.

Some say you can't lock up the rears even with the adjustable proportioning valve fully open or a tee. If that's the case I would look into buying higher quality rear pads.

[CliffBraun]

What are you doing with the car?
A lot of racing you'll want an adjustable valve.
No racing and bigger front calipers with stock rears your balance should be about right with a tee.

I agree, I just put one on my car because I'm going to drill the rotors in the rear. Balance seemed almost perfect with just a T. I like doing things for the sake of doing them though. In other news I have an additional piece of adjustable crap that I need to figure out how to set now.

[PRS914-6]

Never use a T. Where is Eric Shea?..... T is old folk tale that has proven dangerous.

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T is great if you are flat ass lucky that everything balanced but unfortunately there are a bunch of variables including simple things like changing to different pads. The adjustable ones are so cheap I can't see not using one....

[Eric_Shea]

The adjustable ones are so cheap I can't see not using one....

I can. You can still lock up your brakes in the rear causing a deadly spin.

The factory unit is not a proportioning valve; it's a saftey shut-off valve and, it is adjustable. In a panic situation your rear calipers will be shut out of the circuit preventing a spin. I will never have a 914 that does not have this shut off valve.

My advice is to have a properly biased brake system of your choice. If you need a biasing valve to acheive this, insert the factory valve directly after the aftermarket biasing valve for saftey.

Mike... have any pictures of your car? Maybe some before and after shots? (IMG:style_emoticons/default/wink.gif)

[ConeDodger]

The adjustable ones are so cheap I can't see not using one....

I can. You can still lock up your brakes in the rear causing a deadly spin.

The factory unit is not a proportioning valve; it's a saftey shut-off valve and, it is adjustable. In a panic situation your rear calipers will be shut out of the circuit preventing a spin. I will never have a 914 that does not have this shut off valve.

My advice is to have a properly biased brake system of your choice. If you need a biasing valve to acheive this, insert the factory valve directly after the aftermarket biasing valve for saftey.

Mike... have any pictures of your car? Maybe some before and after shots? (IMG:style_emoticons/default/wink.gif)

E,
My factory safety shut-off valve was removed by an expert on 914's who is so far beyond what you know that I cannot imagine you are anything but wrong on this. (IMG:style_emoticons/default/lol-2.gif)

However, in the event that you aren't wrong, are the factory safety valves still available? Second question, if I stamped my factory safety valve with a half-moon and sent it to you, could I be assured that you would send mine back or would you cheat me out of mine and send someone elses? (IMG:style_emoticons/default/hissyfit.gif)

[Eric_Shea]

You funny boy.

Many thanks for the manuals. Check the section on Brake Systems (Chapter 6). There's a great write-up in there describing the unit in detail. 0.1-4/1

My favorite is the very first paragraph; "While braking, the brake pressure in the brake line is transmitted uniformly to the front and rear brake calipers." (read: not proportioning valve) It goes on to say "As the brake line pressure increases, a point is reached (525psi) where the Brake Pressure Regulator prevents this uniform pressure distribution. It limits the pressure to the rear brakes. This increases the road holding ability of the car during hard brake application." Bottom line; you don't ever want your rears to lock up in a 914.

I have a brake pressure regulator I can send you.

[ConeDodger]

You funny boy.

Many thanks for the manuals. Check the section on Brake Systems (Chapter 6). There's a great write-up in there describing the unit in detail. 0.1-4/1

My favorite is the very first paragraph; "While braking, the brake pressure in the brake line is transmitted uniformly to the front and rear brake calipers." (read: not proportioning valve) It goes on to say "As the brake line pressure increases, a point is reached (525psi) where the Brake Pressure Regulator prevents this uniform pressure distribution. It limits the pressure to the rear brakes. This increases the road holding ability of the car during hard brake application." Bottom line; you don't ever want your rears to lock up in a 914.

I have a brake pressure regulator I can send you.

Oh goody! And on my birthday too! Yippee!!!!!!!!!!!!!!!!

[Chris Hamilton]

The factory unit is not a proportioning valve; it's a saftey shut-off valve and, it is adjustable. In a panic situation your rear calipers will be shut out of the circuit preventing a spin. I will never have a 914 that does not have this shut off valve.

I don't see why that is helpful. I thought the idea was just to have the front and rear brake balance set correctly in the first place with a proportioning valve. Or is this purely for a stock 914 with stock calipers and stock rotors?

I've heard that the dealers even removed those things and replaced them with T-fittings from a 911 like most people do now.

Do any modern cars use a system like this?

[PRS914-6]

The adjustable ones are so cheap I can't see not using one....

I can. You can still lock up your brakes in the rear causing a deadly spin.

The factory unit is not a proportioning valve; it's a saftey shut-off valve and, it is adjustable. In a panic situation your rear calipers will be shut out of the circuit preventing a spin. I will never have a 914 that does not have this shut off valve.

My advice is to have a properly biased brake system of your choice. If you need a biasing valve to acheive this, insert the factory valve directly after the aftermarket biasing valve for saftey.

Mike... have any pictures of your car? Maybe some before and after shots? (IMG:style_emoticons/default/wink.gif)

Eric, what you see is a shut off valve. You adjust it to the pressure you want it to limit the rears. For the most part it works the same way the stock ones do and they are cheap and easy to install. I would not run a car without one. I think we are saying the same thing except you can't read.... (IMG:style_emoticons/default/biggrin.gif)

EDIT: One advantage of a stock PV vs some "pressure regulators" is that it allows equal line pressure to front and rear during light braking. This helps pad wear by not making the fronts do all the work on easy braking. It's a nice feature but in reality it just spreads the pad wear around. However, during hard braking and increased line pressure, the front of the car dives and weight transfers to the front of the vehicle making the rear lighter and the reduction in rear braking pressure kicks in and at that stage both devices deliver pretty much the same which is a reduction of pressure compared to the front. I would not combine stock and aftermarket since you may be adjusting the aftermarket for more pressure and the stock one is limiting it.

[PeeGreen 914]

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[john rogers]

The great debate is still on after I first heard this in 96 when we bought our first 914. For many, many years, the master of 914 knowledge, Dave Darling, ranted against using a tee for all the reasons that have been mentioned, including the locking of the rear brakes, etc. Then one day he put in a tee and he loves it, at least at the last PCA Parade when I spoke with him in San Diego a couple of years ago. Having said that, the cars were designed in the late 60s with 60s tires, brake pads, shocks, etc and were designed for european roads which were at that time much worse than ours, narrower, bumpy, etc. The technology of all these parts for a 35+ year old car has gotten much better and the locking of the rear wheels is now greatly reduced. Will locking happen in the rain, hell yes, but then ABS tends to not work well if you have spun and are going backwards either so the answer is to try the tee and see what happens. I would be greatly surprised if your car spins wildly out of control? If you have larger brakes and do a lot of track work, then a manual prop valve is probably the best answer.

[PRS914-6]

Here is the problem.....The factory used a proportioning valve that was designed around parts that were stock on the car at the time it was designed. Now we have better and wider rubber, better pad material and a variety of modifications that we all like to do including larger calipers etc. and this changes everything. The nice thing about these valves is you can adjust them to 0 which acts just like a "T". If you find that the rears lock up too easy you can adjust it in seconds. If you remove the stock valve and install a "T" and it works better it just means that the rears needed more pressure. It doesn't mean "T"s are better than valves. All of this you can do with a aftermarket valve.

Bottom line, if you are dumping your stock one I would install an adjustable valve. I have seen them for as cheap as $35.00. The time and hassle to change out a "T" if it doesn't give you the correct bias is certainly worth installing an adjustable valve the first time and when you change something down the road it's there for you to adjust to compensate. My 2 cents.....ok 5 cents

[PeeGreen 914]

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