rawlz

iTrader: (7)

I am rather confused and am hoping someone could help me out with an issue I've noticed. It is intermittent which has made it even harder to diagnose.

I will start by saying I tried Project Mu Club racers for the first time this past weekend at the track. Very aggressive pads that stops much harder than any pad i've run to date. I felt the brakes engage much higher in the pedal and start to slow down fairly linearly, which was good. I swapped back to Hawk HPS pads to drive home and they were fine. The front calipers (brembo) did appear to be a little glazed.

I took the car out a few days later and I notice that sometimes under light pressure on the pedal it sounds like ABS is engaging but the tires don't lock. The brakes slow down but not fully and the pedal locks from going down any further, even though it's pretty high on the range of motion. If i release it briefly and reapply the brake, it acts normally again and allows me to press the pedal down further (to its normal engagement point) and stops like I would expect. This has happened at least 5 times since and I am worried that if it happens when I need to use the brakes and requires me to pump the brakes this could be an issue. The fact that it only happens sometimes has me completely confused.

I am planning on bleeding the system, but I think air in the lines would cause the pedal to drop further not stay high. No light warnings or anything have come on. I saw this happen on ********** forum to someone a few years ago, but they never posted the solution.

Italianjoe1

iTrader: (6)

Sounds like you might have a failing wheel speed sensor or wheel bearing, I would see if there's any play in the front wheels before you go any further. There have been occasional issues of front bearing failures on track cars and they usually only give a very brief warning before coming apart, if it's losing the wheel speed signal on one corner it could be trying to engage the ABS, and by you releasing and stepping back down it may be seeing the signal again enough to allow normal braking. Just a thought, it may be un-related, but it's the only thing that comes to mind.

Also, if you had access to a scanner, datalog the wheel speed sensor outputs and drive around until it happens, see if one of the signals is dropping out when it happens. There shouldn't be any codes of the sensor is working ok but the reluctor wheel is not where it should be anymore.

rawlz

iTrader: (7)

yea i'll check if there is play in any wheels. I have also heard of that being an issue, especially with R-comp tires, but I didn't think that it would cause this issue. i follow your logic though. If that isnt it, i'll get a scanner.

Thanks!

Blurvision

iTrader: (4)

I have a similar problem. Real deal scanner turns up nothing. Ive swapped ABS pumps and sensors, nothing. Please post if you figure it out.

dkmura

iTrader: (64)

Another factor to consider is differing coefficients of friction resulting from the use of different pads. Most race pads release a small amount of the material on the rotor itself when they get hot. This thin coating is made up of pad material itself and allows for more efficient braking. By switching pads, you may have had two different materials trying to interact with one another and causing the symptoms you describe.

Try using a light sanding of the rotors to remove all traces of the light glaze you see on them (both sides). Then remount the wheels, re-torque and see if the symptoms are still present.

rawlz

iTrader: (7)

I did a great deal of cleaning. I have been swapping brake pads for track days for a while now and always scratch up the surface and bed in the new pads. This is different though. The tires are not actually locking up, but the ABS is engaging.

I have since taken the pads off again, cleaned all the calipers, made sure the pistons are free of obstruction and modulating properly. I flushed the fluid as well. This did not solve anything. I thought so as it didnt do it for a little while. Luckily it did before I got too excited about it, and i limped it back home.

I am going to pull the fuse tonight and make sure its not just an intermitent failure of the actual brake system.

Blurvision- You said you replaced the ABS pump and ALL sensors?! that sounds expensive. I really hope I don't have to do that. I'll let you know if I figure out what the problem is.

Anyone know of a way to remove ABS without losing your speedometer?

RobPhoboS

Any updates on this at all ?