Land Jet

That is what happened, brake pedal pushed but nothing. Very, very little pedal travel but no real braking.

This is a direct quote from the PSM section of my owners manual, "The brake pedal pulsates and it's position is changed during braking, however, it is possible at any time to achieve full vehicle deceleration by increasing the foot pressure slightly on the brake pedal". Not until you release it first will it engage again, at least that is my experience. I have been thinking to disconnect the PSM at the brake master cylinder for track days to see if "ice mode" can be eliminated. The unnerving thing about it is that 99 times out of a hundred, ice mode does not kick in, but on the 100th time it does. Porsche should develop a software fix for this.

onefastviking

When you modify your car with a different suspension, different types of brake pads on front and rear, I'll presume different tires, you can't really expect Porsche to develop a software fix just for you.

On the other hand, there are a few other aftermarket Motorsports ABS brake systems available when you want to upgrade that component as well.

Land Jet

I think it is in one of their algorithms. Regardless of any modifications, when you push on the brakes, they should work, nothing more, nothing less.

I don't expect a fix just for myself, no one should have this problem.

onefastviking

You are 100% correct. It is one of their algorithms, they were set for a car which you have now changed so they don't work like they were originally programmed.

It's ok, I'm just saying you can't expect to have your cake and eat it too. There are always trade offs when making mods, some good, some not so good. You can't blame the ABS issue on Porsches design, nor lack of design, when you have altered the design of the original vehicle as they had built it.

I just think it is wrong to blame Porsche for a deficiency here.

mglobe

My Spec996 does not have PSM, but I have experienced ice mode in it a couple of times. It's an ABS phenomena, not PSM. The car has a far from stock suspension, running on BFG R1's. I just deal with it.

mikew968

in my old 94 968 i only have ice mode when the front or the back are airborne!!!!

Land Jet

Even if the car is modified, why does it only happen once every hundred times on the same braking zone, same ripples, same tires, same suspension, etc.? Are you saying that completely stock cars will never experience ice mode at the track?

bobt993

Larry, I know you are also considering more aggressive pads and that makes the ice mode worse. I have seen this on several 996 NAs and TTs. As viking suggest your next direction is a motorsport ABS system or a dedicated track car.

Veloce Raptor

Hard to say. I have experienced it in my full track M3 when I brake way too hard over a big bump or rise. Just softening my initial brake application has totally eliminated it from ever recurring.

mpaton

And I will pop my head up and disagree with at least the certainty of your verdict.

I have not been following discussions of what "Ice Mode" is (although I've heard the scuttlebutt), but without having been in the car, I do not believe any of the 3 of us can be so certain what it was that happened to Larry.

However I will refer you to a very old post of mine,

https://rennlist.com/forums/1127339-post28.html

and the rest of that generally useful thread. As both my post and Larry's incident deal with 2002 PSM cars, I favor the PSM explanation. For me, its occurrence was never a function of ABS onset, and always coincided with the Yaw Stability under braking component of 2002 PSM. The key linking the 2 cars is the brake pedal pushback.

Bob Rouleau

FWIW my experience is that PSM will kick the brake pedal back hard enough to nearly hurt your foot. This happens when the car (on sticky tires) exceeds the programmed limits of the yaw sensor. I had it with a students 996TT on slicks when I trail braked into a slow corner. I could make it happen lap after lap. PSM wanted to straighten out the car and got me off the brakes rather forcefully! Note this was on an earlier model 2003 I think.

Veloce Raptor

Interesting data point, Bob, thanks. The only PSM/PASM cars I have driven, I have turned as much off as possible, so this really hasn't happened. But, as Viking and Mike Globe alss said, this situation arises in non-PSM cars as well.

Land Jet

That is exactly what I did after my incident and didn't have it happen again. I do think I hit the pedal very quickly when it did happen.

There is a racer on 6speed who disconnects the PSM at the brake master cylinder who says it definitely helps. Here's a photo of the connector. I think I will try this. It leaves the ABS in tact.

Veloce Raptor

Many folks use way too much brake pedal when they up the ante with better pads, stickier tires, suspension, etc.

I would not disconnect that in a car that is still driven on the street and/or is still under warranty. Only on full track or race cars, IMO.

Land Jet

On page 80 of this month's October issue of Grassroots Motorsports, there is a brake pad test of Hawk pads. During the test, the mixing of different pad compounds between front and rear,generated an" ice mode" episode that was captured in a data graph. For those who know how to read it, maybe you can interpret the data for the rest of us who don't know as much. Sorry, I can't provide a link.