964 Cup Car ABS Brain in RS America
02-12-2009, 04:47 PM
#18
Rennlist Member
I'd go out and drive it hard with it both on and off...I went out with the abs switch in the off position, completely overdrove a corner on cold tires and flatspotted both fronts...brain dead thing to do, and I've never had an issue with the non abs cars, but it showed me how easily you can get lazy if with abs always there to save your bacon...
02-12-2009, 05:26 PM
#19
Rennlist Member
Nader - does your ABS unit have the prop valve change (for the more agressive prop valve)? I'm guessing yes? That and/or you're running a more agressive pad compound on the rear...
However, you're barking up the right tree, in that later ABS software also does electronic proportioning of the rear brakes (either in addition to or in complete replacement of a prop valve), and obviously that function will be disabled if you shut off the ABS unit, which can result in locking the rears before the fronts! Woohoo!!!
However, you're barking up the right tree, in that later ABS software also does electronic proportioning of the rear brakes (either in addition to or in complete replacement of a prop valve), and obviously that function will be disabled if you shut off the ABS unit, which can result in locking the rears before the fronts! Woohoo!!!
S2 calipers F and R and after I changed the Frontto to M030 set up. It has happened with same brake compound F and R or less agressive compound on the rears.
The nut behind the wheel must be loose.
02-13-2009, 09:16 AM
#20
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I dunno, man... that should not be possible... makes me wonder what's up with your braking system, if there might be an issue with it. Rears should NEVER lock up first, with the factory setup assuming no major changes... and the changes made for track work (suspension-wise) should only improve robustness against locking...
Unless we're talking some braking in a turn, with very high laterals maybe, something off like that? Puzzles me...
Unless we're talking some braking in a turn, with very high laterals maybe, something off like that? Puzzles me...
02-13-2009, 09:55 AM
#21
Nordschleife Master
I agree with Vaughan, but will add that the only Porsche car that I've found to have a rear brake bias issue is the 993RS which has a rear caliper where the pistons are too large and have too much braking power.
02-13-2009, 07:53 PM
#22
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Nader. Is your corner balance correct for an S2. After my wreck at Mosport, the first outing in the red S2 was a disaster. Aside from the fire, I could not put power down and was locking under breaking. I had yet to corner balance and that fixed all the issues. Except for the fire. 
02-13-2009, 08:28 PM
#23
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Actually, the ABS control unit doesn't care if the wheel is moving forwards or backwards, it still reads correctly. The cut off **** exists because with ABS you cannot put 2 feet in and spin the car, the ABS will activate and will go in the direction the wheels are pointed.
02-13-2009, 09:38 PM
#24
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You can drive just fine with out ABS. With big slicks, especially with a 5% size mismatch, the stock ABS sucks on the track. I replaced it (and saved weight) with a simple Tilton dual master cylinder setup and no ABS. Yes, it took a while to learn to drive without it, but I don't think I'm slower because I don't have it. Note that I don't drive in the rain where it might help and it doesn't matter as we don't get rain in CA anytime between April and October.
02-14-2009, 02:31 PM
#25
Rennlist Member
Nader. Is your corner balance correct for an S2. After my wreck at Mosport, the first outing in the red S2 was a disaster. Aside from the fire, I could not put power down and was locking under breaking. I had yet to corner balance and that fixed all the issues. Except for the fire.
I do not think it is the balance because I had problem with ABS at WG CR last year which was my first time out and the car was just cb and aligned. The rears only lock up under very hard braking even when the wheels are straight and I was able to run the whole CR weekend with only one mis-hap by braking earlier and more gently. I had the system checked after WG and no issues were found except the rotors' screws.
FWIW, I saw another S2 lock up the rears at last year's SP CR and when I spoke with the driver he said that he lost his ABS prior to that.
02-14-2009, 03:18 PM
#26
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All the N/A 944s I have raced have been able to lock up the rears pretty easily. I don't know if I ever locked up both rears at once and spun though.
I think with racing tires you get enough weight transfer to really get the rears unloaded, even with the car being lower etc.
The other thing is that stiff torsion bars generally do a very poor job of keeping the tires on the track when that end of the car is not loaded hard.
All these things add up to a car which can lock the rear brakes.
Chris Cervelli
Spline Technologies
I think with racing tires you get enough weight transfer to really get the rears unloaded, even with the car being lower etc.
The other thing is that stiff torsion bars generally do a very poor job of keeping the tires on the track when that end of the car is not loaded hard.
All these things add up to a car which can lock the rear brakes.
Chris Cervelli
Spline Technologies
