How well do your 911 brakes work ?

[pjv911]

Maybe someone can answer this question for me . I have found that every (at least I think every) 911 car I have driven the front tires lock first under hard braking . I have owned over twenty 911`s and have driven at least 40 cars owned by friends and customers(many different tire configs) . Every car I pushed hard locks up the front wheels first long before the rears . This is when they are hot or cold. This must be the way porsche sets them up . Is this correct ? Am I wrong ? Would braking performance be improved with an adjustable proporsioning valve ? What gives ? Please tell me what you guy`s experience .

Kurt Williams

[autoxracer31]

im using my 74 brakes, and they lock the front tires even when im not braking hard sometimes... i hate them

[anthony]

The system is designed this way for safety. If the rears locked up first the rear end would want to come around.

[TimT]

Yes the fronts typically lock first... its just safer that way.. have the car push a bit.. having the rear brakes lock first can be unnerving..

[vash]

i can never tell, both my eyes and my ass are clenched tightly closed!

[juanbenae]

if i was fast/skilled/smooth enough to actually need them all, then i could tell you.

or if i get to the track this summer and heat them beyond recognition i might gripe.

[SpeedracerIndy]

All of the 911s I have driven (only about 10 or so), including mine, lock the front well before the rear. Kind of negates the steering wheel's function. It reminds me of all the morons around here trying to drive in the snow. They slam on the brakes thinking the car will just stop, then wonder why it slid into oncomming traffic. Anti-lock brakes couldn't be suited for a car more so than the 911. But, as long as you know how to DRIVE a car, you should be able to control it under braking.

[pjv911]

Then why is an adjustable proportioning valve not a common upgrade ? I mean people install turbo tie rods and 90% wouldnt even know a difference . You would think with all these guy upgrading to bigger brakes that a new adjustable valve would be common practice . Where is mr Verberg when you need him ?

Kurt Williams

[pjv911]

There are 4 members who voted that there brakes are equal . But none have posted . Whats the deal ? Does anyone have an answer ? Did you install an adjustable valve . Or your just not sure if they are equal and voted anyway . Inquiring minds need to know . I think this may be one of the most overlooked and avoided flawed characteristics found on the 911 cars . SPEAK UP BOYS .

Kurt Williams

[masraum]

Seems the fronts should lock first. So in odd situations they still lock first. Having the rear lock first is bad. Seems the best answer is to setup a brake system with the proper bias. I suppose different loads could cause a change in weight distr that would require a change in bias, but how many of us really would make it better if we were adjusting because we were half a tank of gas down.

[ZOA NOM]

Fronts lock first, and I'm the last one to question German engineering. It's worked fine for quite some time. Remember, once the rear of a 911 (or any rear engine car) loses traction, it quickly swaps position with the front.

[Ed Bighi]

I used to have this Toyota truck that would lock up the rear just a hair before the front. That was actually quite common with trucks prior to abs being installed in them. Remember that trucks got abs very late in the game, even though they needed it the most. Considering that particular truck was quite fast since it was supercharged with a lot of mods and had a good ammount of weight reduction, it could get hairy at times. I also had a couple of buddies who got pretty scared when they locked up while driving it. With the triple digit speeds at the time, they needed fresh underwear afterwards. But as was always the case, the thing would have the rear swing one way or the other about 40 degrees and stop there. Better than a full spin. The other problem was when the thing got traction again, it was usually pointed in the wrong direction. Unless the driver knew what he was doing and kept the rear in line with the wheel. Looking back, it needed adjustable brake bias badly. It was just way too fast to go without it. Ideally, one would adjust the knob to get the front to lock just a hair before the rear. Even then, trail braking on entry would still aid in rotation, which is needed on a front engine vehicle. All Porsches and most cars today come with a little more than that margin for safety. It's a heck of a lot easier to modulate front lockup than controlling oversteer under heavy braking. Regardless, I sometimes find myself doing exactly that in my 911 during some very late braking entries. Countering oversteer on entry isn't something for newbies to attempt mastering while they are still at a stage where they find the 911 unforgiving.

[911pcars]

The ideal would be to have the fronts lock up just before the rear brakes. The ideal makes the maximum use of both front and rear brakes. We assume the rear brakes help, but how many of us really know how much the rear brakes contribute other than not locking up first?

An adjustable brake proportioning valve is a good idea, but for many owners, it's not a straight bolt on affair. New lines have to be fabricated, adapted and routed to and from the circuit to the valve. And there's a matter of testing braking thresholds to determine the best front-to-rear setting or connecting a set of pressure gauges to the front and rear circuits. This is a routine adjustment when setting up a track car for the track, but less easily or conveniently performed on a street car for the street.

The factory setup works fine for most of us. However, when one deviates from the normal front-to-rear weight distribution (deleting weight, frt/rear tire variations, etc.), even upgrading to larger calipers and rotors, there's something to be gained by fine tuning the brake system.

Light weight and braking prowess always helped separate Porsche from the competition.

Sherwood

[kqw]

I am sure everyone has noticed that the front brake pads are larger than the rears. And..as we all know, Porsche has always been known for their effective brakes.

Back in college, one of my roommates had a 1965 Pontiac Bonneville (BIG CAR) that had "Power Brakes"..... If you were not real careful in applying the brakes, you could go through the windshield....

[Mark McClure]

This one I can have a stab at. If you consider the physics of it under hard braking the forces are acting forward. Therfore putting more weight on the front end. All of your stopping power is directed at the front wheels. Obviously locking them up is bad as it actually collapses the tread and reduces the adhesive qualities. As for the rear.with reduced forces on them the rear tyres have less traction. Locking them first is a very bad thing as again causes the tyre to lose adhesion resulting in the back end coming around the front.

I used to race bikes and this example represents it a little more graphically. Very few racers use the rear brakes for stopping. They are feathered to keep the rear in the right position or to chance the positioning as you approach a corner. Since a car only has one pedal the braking bias is setup on the front. Adjustable compensation whould be great but unfortunately very few of us can drive a car well enought to set it up right.

Cheers

Mark.......

[jluetjen]

OK. I voted for "All 4 wheels are proportioned perfectly", but then I have a dual-master cylinder set-up with a dash mounted bias adjustment in my car. So I doubt that my input helps the conversation much.

BTW, I'm not sure if it would be a cost-effective upgrade for most people since it cost about $1500 all up (including replumbing the system, a pressure switch for the lights, etc) and me doing the installation. The only reason that it made sense for me (or so I've told myself) is that I had a bad master cylinder and my car's destiney is to become an SCCA Production race car where this upgrade is allowed. So I figured I'd make the investment now rather then later and skip spending $100 on a new MC that I was ultimately going to throw away.

[Silveresrty911S]

Mine locks the rears first !! (when using the e-brake for flying bat turns)

Fronts first when getting a little aggresive on the Ax track.

[Glasgow 911SC]

Mine locks the fronts before the rears. The only problem is that the front left goes first! I've rebuilt the calipers twice and even swapped the fronts for a 2nd hand set I bought. Eventually something else seems to pop up. I'm thinking of an upgrade soon.

[svandamme]

rears first, nasty when emergency braking for a traffic jam
big pile of smoke, and going sideways
that hard as rock brake pedal of mine doesn't help much to dose my hard braking...

[Bill Verburg]

ideally you don't want any thing locked unless you are off track.

Since we don't have ABS and are not always prefect drivers the safty solution is to have the fronts lock a tiny bit before the rears. This is a skill theat northern drivers get to practice a lot this time of the year. The California, Az. and Fla drivers don't know what fun they are missing and how well honed our track skills get during Dec - Mar.

Theer is no such thing as perfect bias, every different car setup and drver style wil want something a little different and to add to the cinfusion bias is dynamicly varible. What is great at 20mph can be frightening at 120mph

Adjustable bias is theoreticly a great idea, When I raced motorcycles you learned to automaticly dial the exact bias that each situation wanted. The rider is an integral part of the control system.

Unfortunately the driver of a car is much less integrated and having another knob to twiddle in a fast changing situation is contra indicated.

Most folks w/ adjustable bias might touch it once a day. Maybe

An automaticly functioning p/v can also be a useful tool, there are 2 kinds, one is pressure sensitive the other is responsive to chassis movement. BOTH HAVE THIER USES.