Darren

The faster I get my 996 race car going the more ABS problems I'm running into. I've experienced the infamous "glide mode" or "ice mode" particularly if I brake too hard -- what happens is that if I use 100% of my braking force, I'll feel the pedal come up a little and then the car doesn't slow down nearly as well as it should.

My car is a 2002 996, Hoosier slicks, Moton triples, GT3 calipers, etc, very similar to a Cup Car without the right motor. Tires are equal diameter front to rear, 250/650-18 and 305/645-18.

This past weekend at Thunderbolt I started having an issue that if I ran really hard, I'd get a code thrown for "Steering Angle Sensor (code 4420)" which, if I'm understanding correctly, is the lateral g-force sensor which is getting an out-of-range signal, presumably because the car is turning faster than the ABS knows how to deal with. This was happening consistently at the long decreasing radius turn where I use the ABS every time. As soon as this code is thrown, the ABS is disabled, as I realized in the following T1 when the fronts locked up.

I've called around several shops and it sounds like these issues were found with the Koni cars, and in most cases people decided to scrap the stock ABS system.

I'm looking at basically 4 options and I'm looking for any advice or opinions:

1. Something else is going on, maybe tire size which is 3.2% taller than stock
2. Scrap the ABS and install dual manual masters from 997 Cup (Maybe $2000?)
3. Install the Motorsports ABS unit (Maybe $6,000)
4. Install the Bosch M4 Standalone ABS (Maybe $11,000)

Rassel

If you put on stock wheel size and tires. (Stock circumference)
Do you still get the problem?

Darren

The challenge there is that I'd have to find slicks with exactly the right diameter, but good idea!

jrgordonsenior

What does your car weigh with you in it? Koni cars mostly went with Bosch's expensive M4 system but they are heavy pigs at slightly over 3k empty. Obviously all that weight has an impact on the braking system. Hopefully you have your car down to 2800 w/driver or less.

I'm guessing the GT3 calipers excert so much more force than stock calipers that you're exceeding the capabilites of the ABS unit. The Pagid GT3 2407 pad is 86% larger than the stock 2405 pad. That's a massive increase in braking power. What are the costs for the OEM GT3 ABS unit? That might be your most cost effective solution.

FWIW, I kept the OEM calipers and rotors for weight considerations and I'm running at about 2675 w/driver also in GT4. I occasionally have ABS issues, but it's usually from marbles, a rough transition, or worn out pads. I brake 99% initially slowly releasing into the turn. I use RS19's front, RS29's rear for balance...

I don't think tire diameter has anything to do it. I alternate between Yoko or Michelin cup slicks without issue and they have a 6.5% delta in diameters. I have run your Hoosier slicks setup and like it a lot though I would advise against using the lower profile rears (645's) on a banked track like Daytona....

Darren

I've been reading up and it sounds like the GT3s have many of the same issues with the ABS system. The 996 GT3 Cup ABS would have to be fine for my car I think. I guess the issue is a street system which is designed for safety on the street vs a motorsports ABS system which is designed for max performance, trail braking, etc...

My car is 2825 with driver, soon to be closer to 2750. It's good to know that you are running even taller tires and having less issues.

I'm thinking that you're right in that the size of the calipers is having an effect -- too many things are non-stock and I think the ABS system is falling off the map of what it knows how to deal with -- car weight changed, calipers changed, super grippy slicks, and race conditions.

onefastviking

Do you have 3 channel or 4 channel ABS ?

Darren

4-channel

onefastviking

Pro 996 racers also went up in brake force and rotor size,although not GT3 big, they still had the same "black ice" conditions until they changed the ABS systems. If you want it totally cured the Bosch Motorsports is the way to go, it's not cheap, but it works.

bobt993

race conditions?? chasing me??

jrgordonsenior

Or go backwards to OEM like I have. I'm guessing a bit here, but I'd bet the GT3 calipers and required rotors, wheel carrier, bearing, etc. all combine to weigh about 5 lbs or more per corner. That's a huge amount of unsprung weight. Did you ever compare the weight of the parts?

Viking what do you run on Jay's car?....

Darren

Oh they are heavy, no doubt. The rotors alone are very heavy. I have the GT3RS uprights on my car and I would like to keep in that direction. I was also having issues with the stock brakes in that I couldn't keep the dust boots from getting destroyed by the heat. I also disliked going through pads so frequently. I know plenty of people race on the stock 996 brakes but there is a reason that the Cup Cars run the calipers that they do.

jrgordonsenior

I run 3" ducting from the front grill to the rotors and don't suffer those issues. Hell I have the same rotors that I started with last August, and just changed front pads for the second time, once for the rears. Miscellaneous practices plus 10 race weekends....

Darren

I don't know how the tracks are on the West Coast and whether that makes a difference. If there wasn't an issue with the stock brakes and ABS system then the Koni cars would all be using them.

Land Jet

I upgraded to the GT3 brake system, and with an instructor in the car I weigh in at about 3800. I have not had any brake problems using SRF, RS cooling ducts, Toyo 888's, and 350mm rotors. I don't think weight is your problem. Maybe the stock ABS unit is past it's prime.

Darren

I'm sure it works well in a mostly stock car. My car is a dedicated race car, fully gutted, being driven 10/10ths, with full slicks. If I drive 8/10ths then its fine, there are no issues.

No offense but it's not possible for you to be pushing that hard or stressing the system that much with an instructor next to you. You certainly aren't pulling the same sort of g-forces.