Stuttgarter

I KNOW this is not the case. I spent years of my life trying to push as hard and fast on the pedal as I possibly could. After a little while you get very good at it and you have to consciously try to brake like a "civilian" who doesn't spend all day at -1 longitudinal g. This may be related to the delay between WOT and braking but it is not related to the rate of the brake force increase.

The reason for this is the way the OEM specs are written. They measure braking distance from the moment the brake light switch is active. The harder and faster you push, the shorter the braking distance and thus the more likely you are to meet the OEM spec. If we squeezed the pedal more gently, we'd never pass the spec.

Can anyone reproduce this on the street with OEM wheels and tires? If so, they should demonstrate it to the dealer. It may be better if any real investigation originated from Porsche.

ADias

That is supposed to preload the calipers and apply extra pressure faster... so if it does not it is a bug.

Nugget

That's not true for RWD 997.1 cars. The brake pre-load was only on the "4" cars with the 997.1.

I think the GT3 does it, though, and I also think that 997.2 cars all do it, but I'm not sure.

Fritz Flynn

From what I can tell this is only happening on road courses and as mentioned I think the biggest factor is the speed at which you go from full gas to full brake not how hard you push the pedal but typically if you are not being smooth and your foot is responding in a more reflex type jabbing motion you're time from gas to brake pedal is shorter. When your adrenalin is pumping it's a much faster motion that may be hard duplicate on the street coupled with the fact that it's not wise to practice 120 plus MPH brake test on the HWY.

As has been mentioned it's possibly a vacuum/brake booster issue resulting from pressure loss while under full throttle for extended periods and it's not ABS at all but everyone seemed to shoot that one down and that was my 1st guess and it would certainly cause a high stiff pedal with little braking power when trying to slow ASAP as late as possible from 100 and up on road course.

Thanks for taking an interest in this very real, very scary problem and lending your knowledge of the ABS system to help figure it out

Bob Rouleau

I do about 50 track days a year and have never had ice mode on my 996 or 997.1 and .2 RS. I build brake pressure slowly at first. I want to transfer weight first to avoid triggering ABS. Seems to work.

cfjan

Does the 6Cup ABS have similar issue? If not, I wonder what's the difference in the programming / logic between the 2 ABS controllers..

Fritz Flynn

That's good to hear Bob.

So far so good here as well but it does appear some experienced drivers are having issues and this problem occurs before the pedal even moves 1/4 inch it's like you immediately have a rock hard pedal that doesn't move. Again scary stuff and hopefully we'll continue to have good luck or possibly we are braking slowly or smooth enough to not engage this bug.

Hopefully someone will figure the mystery out and we can all stop speculating.

Fritz Flynn

Someone mentioned using the ABS from a cup and it fixes the issue but cost like 10k.

Terry L

A friend who is a racer started to encounter the problem when he moved from Hoosiers to pure slicks. He investigated the costly Bosch race ABS system but finally solved his issue by switching to less aggressive front pads - I think he went from Pagid Blacks to Yellows (RS 29s). The best working hypothesis I have seen is that the combination of stiffened suspension, highly sticky tires and aggressive brakes takes the car outside of the parameters of the street-biased ABS system. It isn't designed to see such high deceleration or something and reacts by reducing brake force. Bumps in the brake zone are another contributing factor. The trouble is that all of us want to extend the WOT zone as long as possible and brake as late as we dare.

turbo911cm

TerryL is right on.

The Bosch ESP/ABS system is only guaranteed to Porsche to work with OE tires, suspension, pads, etc. There are algorithms in the system for high speed driving/braking, but again only on OE specs.

As soon as we start playing with this, we start falling out of the range of the algorithms and we get ice mode.

We as enthusiasts are going to face this dilemma more and more in the future as cars have more computer controlled features installed in them.

Nordschleife

The ABS system is exhaustively tested, under all sorts of conditions. However, the @envelope@ does not include slick tyres.

The Bosch race ABS is easily programmed and is switchable to several different programs as required.

VLN drivers are using the motorsports ABS when they can and even refining the stability/traction control systems where allowed.

If you have tyres that closely mimic the characteristics of slick tyres, street ABS will degrade braking performance and it should be disabled under these circumstances, this may entail a visit to the fuse box.

I have found that fallen leaves on the road surface cause ABS conniptions - there is no easy fix for this.

If somebody wanted to market a decent number of the ABS M4 kits properly programmed, I'm sure the price would come down. At present the raw kit comes in at between €5,900 and €6,900 depending on connectors.

R+C

Spiffyjiff

i'm sorry if i missed this in a post but...

much like ECU tunes for horsepower etc, is it possible to "tune" or re-code the stock ABS module? or are the only options to: keep it stock, lay out huge $'s for race ABS, or "just deal with it"?

Stuttgarter

As a former ABS engineer I beg you not to do this. Pulling the ABS fuse on a car without a brake force proportioning valve will mean equal brake caliper pressure front to rear. This will cause the rears to lock which will create an unstable yaw moment and likely spin the car.

997's have EBD, as discussed earlier in the thread and in detail here.

http://e30m3project.com/e30m3perform...abs/page-2.htm

If you pull the fuse on a car with EBD, the red brake light will come on. Red lights mean do not drive, tow to the mechanic. If you pull the ABS fuse on a car with a prop valve (no EBD), only the yellow ABS light will come on. In this condition the car can be driven carefully.

In cars with EBD, some failures, front wheel speed sensor or front valve, will cause the yellow ABS light to come on but the red brake light stays off. This is because ABS is shut off but EBD can still work and the car can be cautiously driven.

Incidentally, I had an e30 M3 with aftermarket pads, rotors, wheels and tires. I bought the car with an ABS cut off switch which I used as the car had a prop valve and no EBD.

Nordschleife

Stuttgarter

Imterestingly, a PAG person was demonstrating some aspects of this problem and he may have been taking a few verbal short-cuts when he explained that disabling the ABS was a just a fuse cut out. However, the car was cycled threough a complete shut down each time the switch was changed.

R+C

PS I shall be spending some time on track with a person from Weissach who tests all the racing 997s prior to delivery. I'll ask him if he can ellucidate, further.

Stuttgarter

My first reaction was there must be something about more modern systems that I don't understand that would allow someone to disable the ABS while keeping EBD and maybe ESP/VDC/ PSM (?) active. The more I thought about how this might be possible the more I believe that whoever you talked to either mis-spoke or is mistaken.

Yes, you can disable the system by puling a fuse but if he was suggesting you do this that is reckless.

-Noah