Ritter v4.0

3 events ago I was running stock 996 brakes with Cobalt pads and Motul fluid. No complaints. Good stopping power and little fade.
Never had ABS kick in.

Switch to new stock rotors and Pagid Yellows/Blks and the brakes started locking up and flat spotting tires because the ABS is not kicking in. Switch back to Cobalt pads and same issues.

So two probs: lock-up and no ABS. I can live without the latter if I don't have the former.

Porsche/Bosch Hammer says ABS is functional. ABS ground is fine and sensors have been blown clean. I've never had ABS so this may not be a recent occurrence.

Seth Thomas

Dave when in the brake zone are you getting the lockup? As soon as you hit the brakes? Middle of brake zone? about 50ft before you are about to release the brakes?

Ritter v4.0

Cont'd

Could the lock-up issue be suspension related? The JRZ doubles have seen a lot of work in the last two season and are coming off the car for a rebuild next week.

Ritter v4.0

Seth if I attempt a threshold brake they lock, so instead last couple of events Ive had to go to MBS ( M for manual). I squeeze them on gradually but quickly until they start to lock then release gradually (but quickly).

Ironically I've set my best times recently and in race conditions but with relatively open track. More gas/ less brake? But with traffic it sucks.

Seth Thomas

Gotcha. Sounds like you are learning to use your brakes less and more efficiently. :-)

Something else to consider if it hasn't been done in a while is a caliper rebuild. The heat the stock 996 calipers are seeing while racing wears on them after a while. We rebuild ours every year at a minium on any of our cars.

I can see how the shocks can cause some issue with the car but it should be felt at other spots on the track. The ABS would also be kicking in if it were funtioning properly if the shocks aren't working right. My guess is you have an ABS issue and are driving the car harder now than 2 years ago.

Have you tried getting the ABS brain from another car and trying it on yours?

jrgordonsenior

I'd double check that ground for continuity and then replace the front ABS wheel sensors. Since this only occurs since you removed your headlights I think that's the most obvious cause as the ABS grounds thru the headlight connection. Its the thick brown wire that runs to a bolt on the frame rail in the trunk on the driver's side. Everytime I've seen this issue it's that same ground. I'd try interruping the ground and ground it elsewhere additionally to be sure....

Seth there's no OEM rebuilding kit for the 996 calipers. I just buy a pair of junk yard calipers every year or so....

onefastviking

If I'm not mistaken the Cobalt pads really need a fresh rotor, if the problem followed the change to the yellow/blk Pagids then still once changed back to the Cobalts it could be that the Cobalts picked up some of the Pagid material and are partly causing the problem.

JR's point as well is very true, that ground can be an issue.

Also, the suspension if working too hard,fast, like a bumpy track, can cause the issue. Rebuilds every 2 years is really the max time limit I would do, especially with the JRZ's, IMHO.

If you have old data to compare against the most recent data then I would do that to help figure out which area you should be looking the most at.

If I remember correctly then you have a fairly light 996, the calipers do pretty well if you have decent air to them. You can also upgrade rotor sizes and get some more clamping force if needed. I took the stock 996 calipers pretty far before finally giving in and going to a larger caliper.

onefastviking

Have you changed any tire size or compound recently ? Running a mis-match of old/new tires ?

Seth Thomas

This can cause some issues but it should not effect the ABS from not functioning. A malfunctioning ABS system usually has a culprit of bad sensors, bad control unit, bad ground, etc. Especially for one that used to work and now it doesn't. The electronics for the system would be the first thing I would check and replace.

Ritter v4.0

No change in tires- same sizes and compounds.

The locking issue exists with both pad types on the stock rotors. Worse with the Pagids as we also installed huge ducts which in 36-60F recently would not allow any temp to build. I drove two warm up laps with the brakes on and they were still not up to temp. Midway through the race, I've was little too heavy on the pedal. Result; lockup and smoke. Happened more or less last w/e in ambient 65F with the Cobalts. Long double yellow but with riding the brakes for a couple of laps before going green. Same result.

The ABS has never come on since gutting and converting the car. And the "gutter" is long gone, but I do recall two other cars of his making having ABS issues (i.e. no ABS). Until recently I just assumed mine was working.

onefastviking

I agree the electronics can cause problems and should be checked, especially the sensors and the grounds, honestly it's almost easiest to just add some grounds to make sure there are no issues with grounds. Also the wiring harnesses can cause problems as well and are common to have issues.
But, the OP stated that the problem started after running Cobalts and then making a change to Pagid Y/B's and has checked the grounds and the sensors already.
From my experience, which I have a little experience with these 996 brakes, as well as the reprogrammed Teves, and Bosch Motorsport systems too, the stock 996 system will, or can, cause some weird issues like the OP complained, thus my advice would be to check all that you, and JR recommended, as well as a change back to a "new" fresh rotor and the pads and fluid that worked well before an issue arose. If all else it's an easy way to rule a couple components out of the failure mode.

The reason it can cause the ABS failure mode is the reason GA approved the "reprogrammed" Teves systems. The ABS isn't programmed for some of the situations we ask it to perform in and then it just doesn't know how to respond properly.

Just my 2 cents, no worries if no one takes my advice, my brakes are working just fine.

onefastviking

One other quick thought, and easy to check too, are the wheel brgs ok ?

Veloce Raptor

Dave, as I mentioned when I saw you, IMO ditch the huge ducts in cool weather--too much brake cooling at a track like RA.

And if there is a pattern of the car stripper disabling ABS (likely when removing headlights), that is why ABS is not coming on. So a combination fault: brakes remaining too cool + no active ABS.

onefastviking

VR, could he just cover the inlet for the ducts ?
Run temp strips to determine where the temps are, you should know where the sweet spot for your pads are to make sure you are optimum.

Ritter v4.0

Replaced a wheel bearing last w/e trackside. HAd probs before and after (with brakes that is).

I do have a set of '03 version Cup calipers and rotors available to me for near nothing - worth the upgrade or more weight and headaches?