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

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

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.

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.

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.

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

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.

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.

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....

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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?

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.

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?

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!!!!!!!!!!!!!!!!

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?

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....

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.

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.

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

if I'm using 84 carrera brakes front and rear...what about using the regulator that came with that brake setup? When I removed it from the 911 it seemed to be inline for the rears?

Paul, your valve reacts to pressure in the system? I guess I wasn't reading!

* Shut off Valve or (factory) Brake Pressure Regulator = Shuts the rears off in a panic brake situation.
* Proportioning or Bias Valve = Changes the proportion of hydraulic fluid going to the individual circuits (bias) but will not shut down the rear circuit completely. If you have it limited so the rears do not lock in a panic situation, you're not getting the full effect under normal braking. Sorry... the brake pad wear thing doesn't hold water. That just means the rears aren't working when they could or should be, afterall; how much time do we spend in a panic braking situation? Why adjust to it? This, I feel, is one of the major problems when people complain about 914 brakes. I believe a full 80% of the rear calipers out there are effectively in-operable. The adjustable valve is linear, it knows nothing of pressure. It does not shut down the rear circuit.

If your rear calipers have the ability to lock in any situation, you face a much higher risk of an uncontrollable spin in a 914 (Read Vic Elfords book, page 55). It has nothing to do with calipers or tires. It has everything to do with low polar moment of inertia which doesn't change with the tires or brakes. One of the significant effects on handling is; it rotates on it's axis extremely quickly. (well... kinda with tires but, it compounds the problem, when they finally do let loose, you'd better be paying attention or insurance premiums)

Again, this has nothing to do with stock -or- aftermarket caliper components. It has everything to do with increasing the road holding ability of the rear of your car in a panic brake situation. It says so in the factory manual and the physics are explained in Vic's book.

Changing the bias on what was already a matched set of calipers is the owners prerogative. Some see the need and some don't. "Most" people in that situation feel they need "more" rear brake not less, but... YMMV. You can still install an adjustable bias valve and retain the pressure regulator. Taking out the brake pressure regulator is dangerous for your car, yourself and your passengers IMO. Again, maybe Dr Evil can weigh in with before and after pictures of his car (and passenger).

I believe the 911 received one shortly after the CA 930 crash/law suit.

I guess we just disagree......No problem. However if you think tires don't have an effect on brake bias go put an R compound tire on the front and a worn out skinny tire in the back and watch what happens...or vice versa.

If you don't think pads have an effect on bias try changing the compounds on the front vs. the rear and go stomp on the brake.

If you don't think calipers have an effect on bias, put a 930 Turbo caliper on front and leave the rear stock. The factory matches front to rear precisely to the car. Even rotor size has a huge difference on the playing field.

I'm not making these comments from reading a book, they are real experiences.

If you deviate from stock, brakes change. While a pressure regulator is not the ideal solution it is far better than using a "T" if you are treading to the unknown.

Here is a pressure map of the 914 regulator. As you see it allows equal pressure up to a point and then REGULATES. Most aftermarket units do not have this feature but you can adjust it to not overpower the front. The stock regulator only stops pressure from going above the regulated pressure, it doesn't stop it all together. So again, you get a higher pressure in the rear at light pedal travel and regulated pressure when you stomp on the brake hard. Here is a chart out of the factory manual that demonstrates this. If you added a line in the chart for an aftermarket unit, it would be regulated the entire length and not half way up. I'll leave it be at this point....but if you like reading on the subject this one is not bad LINK

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The 914-6 brake system is more then adequate in the stock configuration "when working proper"In a stock car..When you put a big motor in a 914 you need bigger brakes!!more wieght, more speed ,more brakes, its simple...But I would never put just a T in the system unless you wanna be a crash test dummy. I think Porsche engineers are just a bit smarter then all of us...But hey its your car and your life lets just hope no one else is involve in your fuck up..JMO..If you have plans for tomorrow drive safe today

Very interesting stuff.

Seems to me it's high time for a list of good brake SYSTEM upgrades, as a system.

Like a lot of people out there, I'm running 911 M calipers up front and 914-4 stockers out there, with no other upgrades but the 19-mm master cylinder. Frankly, it's kind of a "oh hey, it fits and got me five-lug wheels" conversion, and it seems to me that I am not getting enough rear braking anymore. Especially given the fact that my latest set of 911 front rotors are ever so slightly warped.

I'd like to better understand caliper piston-sizing as it relates to the 914 (I understand the basics) and, especially, as it relates to "911 front with stock rear" upgrades. M, A, SC/Carrera calipers are all most of us need up front, but then the question is how to match these in the rear without converting to the 911 parking brake setup. Or, is that the only way to go to do it right?

I've still got the regulator and it's not going anywhere, but I would be interested in getting my rear discs to do more of the work....

Eric?

pete

PRS914-6:

Where did you get that chart? (just wondering)



Are 914 and 914-6 valves the same, just adjusted at the factory differently?


Wes V

Factory Service Manual

This is what I use: http://www.hrpworld.com/index.cfm?form_pro...;action=product

( the lever type, in the metric size )