Urgent Help Needed: GT4CS Ice Pedal
08-31-2017, 05:58 PM
#1
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Urgent Help Needed: GT4CS Ice Pedal
Campaigning a Cayman GT4 MR in a 24H event this weekend. Our car has been suffering from inconsistent brake pedal feel all day, sometimes hard sometimes soft. Some of the drivers with a heavier brake foot are experiencing "ice phenomenon:" a rock-hard pedal and significantly reduced braking output.
Data would show that the ice pedal happens at the start of braking, and that the car can be brought to a stop with very extreme braking pressure (normal is 90-100bar, one driver had to put in a well over 200 bars to brake into a corner.
Thus far the following aspects have been checked:
- ABS is not getting triggered
- Brakes have been bled
- The inconsistency in pedal feel happens, with or without the ice pedal issue.
Has anyone encountered similar issues? What were the culprits for you? Any pointers will be helpful as race start is quickly approaching...
Data would show that the ice pedal happens at the start of braking, and that the car can be brought to a stop with very extreme braking pressure (normal is 90-100bar, one driver had to put in a well over 200 bars to brake into a corner.
Thus far the following aspects have been checked:
- ABS is not getting triggered
- Brakes have been bled
- The inconsistency in pedal feel happens, with or without the ice pedal issue.
Has anyone encountered similar issues? What were the culprits for you? Any pointers will be helpful as race start is quickly approaching...
08-31-2017, 06:02 PM
#2
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I have heard that this is a known issue on the 981 GT4 CS. Suggest you either go with the full Bosch M4 system or experiment with brake bias by running different pads front/rear. Search in the Cup Car section for more info on this.
08-31-2017, 07:19 PM
#3
I experienced "Ice Pedal" many times in my 987 Cayman S. PFC looked into the issue and concluded that the ABS was confused and bled pressure from the rear brakes. There are some videos around explaining this. Their recommendation was to try an initial "soft" brake application immediately followed by hard braking. I used this technique and believe it helped. If you do get ice pedal, a quick release of the brakes and reapplication fixes it. I have not had issues with the stock GT4.
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519Kris (05-19-2021)
08-31-2017, 10:24 PM
#5
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Here is a little more detail:
The clubsport does not come with a M4, its a modified street unit. The new 991R originally came with a teves but in a recent update they changed over to the M4 because drivers complained about the pedal feel of the teves system. I have driven both and the bosch gives you more feedback when pumping pressure back to the pedal. The teves feels numb and its hard to tell if the car is into the abs. They both work fine but personally I like the bosch better. I like the map selector switch and the ability to get custom calibration for the individual car with the m4. Also I was under the impression that the teves was a reprogrammed street unit which may or may not be correct. The m4 has many motorsport only changes internally to help the unit function much better than a street based system.
The clubsport is the M4. Same unit and programming. The only difference is that it doesn't come with a custom wiring harness. The custom harness is what drove the price of the M4 way up. The clubsport is just under 8K.
I believe the "ice mode" some of the clubsport drivers have experienced is due to the power assist of the brake's. It's too easy to add way too much pedal pressure way too fast.
The clubsport is the M4. Same unit and programming. The only difference is that it doesn't come with a custom wiring harness. The custom harness is what drove the price of the M4 way up. The clubsport is just under 8K.
I believe the "ice mode" some of the clubsport drivers have experienced is due to the power assist of the brake's. It's too easy to add way too much pedal pressure way too fast.
09-01-2017, 01:05 AM
#6
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Thread Starter
Thanks for the quick thoughts. Nizer's video hits it right on. We're attacking the pedal in the CS like we're on an unassisted car when we need to give the CS's "gentleman" system more "rolling on" of the pedal. There's good correlation: the two drivers this is happening to (myself included) come from non-ABS backgrounds...
Fingers crossed that we'll solve it when the paddock opens in a couple hours...
Fingers crossed that we'll solve it when the paddock opens in a couple hours...
09-01-2017, 03:06 AM
#7
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The GT4CS likes the touch and squeeze approach as opposed to stab/punch.
The 70L tank car has GT2 street booster.
This system works good however it does not like last minute panic reactions...
The 100L tank dual master system has very firm pedal feel and is more foregiving on the ABS, but you still cant punch it. You have to squeeze into it.
The 70L tank car has GT2 street booster.
This system works good however it does not like last minute panic reactions...
The 100L tank dual master system has very firm pedal feel and is more foregiving on the ABS, but you still cant punch it. You have to squeeze into it.
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09-01-2017, 02:54 PM
#8
09-01-2017, 06:06 PM
#10
Three Wheelin'
Originally Posted by Bill Lehman
I experienced "Ice Pedal" many times in my 987 Cayman S. PFC looked into the issue and concluded that the ABS was confused and bled pressure from the rear brakes. There are some videos around explaining this. Their recommendation was to try an initial "soft" brake application immediately followed by hard braking. I used this technique and believe it helped. If you do get ice pedal, a quick release of the brakes and reapplication fixes it. I have not had issues with the stock GT4.
09-01-2017, 07:10 PM
#11
09-01-2017, 11:21 PM
#12
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09-02-2017, 02:40 PM
#13
Street GT4 with race pads/slicks requires a soft initial start and then a quick ramp up (not step function pressure), otherwise there is a very early onset of ABS and a greatly reduced overall ability to brake. It's much much worse on a bumpy track like TWS. I know it's not the same as the CS, but if they use the same ABS controller, it might behave similarly.
09-02-2017, 08:38 PM
#14
Instructor
I've been having it a lot with my GTB1 Cayman at Road America this weekend and I think a lot of it has to do with pad compound. I have a pro driver coach with me that drove my car and we have figured out that a pretty firm initial hit at the brakes, but then easing the pressure deeper into the brake zone gas kept the ice pedal from happening. I think a lot of what people have already said makes sense, but pad compound is going to be a huge player here! Best of luck!
09-07-2017, 05:24 AM
#15
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Thread Starter
Thanks everyone for the quick responses. We did identify a problematic master cylinder and replaced both before qualifying. The ice pedal problem became less pronounced but remained.
Like others have said here, our conclusion was that the ABS in the Cayman just couldn't handle a sudden spike in pressure (unlike how one would brake a Cup or R). One really had to roll on the brakes like a track day driver... much appreciate the headsup!
The race: we were on a roll for the first 8 hours but sadly the coolant expansion tank exploded at the in-lap of my second stint. That was a race-ender... the team was really quite gutted as we had the pace and consistency for a class P2 and a repeat of our Dubai podium was achievable...
This is probably our last time racing the Cayman. The GT4 field is getting very competitive with offerings from AMG, Audi and McLaren; the Cayman's sadly outpaced and outdated in this bracket, not to mention reliability becoming an issue with older cars...
The master cylinder:
Race day (Photo Credit: Petr Fryba):
Like others have said here, our conclusion was that the ABS in the Cayman just couldn't handle a sudden spike in pressure (unlike how one would brake a Cup or R). One really had to roll on the brakes like a track day driver... much appreciate the headsup!
The race: we were on a roll for the first 8 hours but sadly the coolant expansion tank exploded at the in-lap of my second stint. That was a race-ender... the team was really quite gutted as we had the pace and consistency for a class P2 and a repeat of our Dubai podium was achievable...
This is probably our last time racing the Cayman. The GT4 field is getting very competitive with offerings from AMG, Audi and McLaren; the Cayman's sadly outpaced and outdated in this bracket, not to mention reliability becoming an issue with older cars...
The master cylinder:
Race day (Photo Credit: Petr Fryba):