gbhstrat

Has anyone with a 996 with red turbo brakes experienced a partial brake lockup under threshold braking at the track? My turbo started doing this obnoxious behavior on turn 3A at Pacific Raceway. The brakes are stock reds with Coleman rotors, aluminum hats, and Castrol SRF bake fluid. The first DE day this year I had Pagid yellows. For the second DE I swapped the yellows out for a set of oranges and I experience the same condition (I have yellows in the back). When I test the brakes on other areas of the track, the antilock comes on but there is no lock up. The lock up only occurs when I am diving into the turn 3A. When the brakes lock up it sends me straight and I either have to save the turn with a late turn in or shoot down the escape road that was made for this corner. I can almost sense when it’s going to happen, if I brake early and stay in a straight line, I can feel the antilock start to come on and back off a little and have additional time to slow down and initiate the turn. This is how I am forced to run each lap now. However, when I start to push the car hard into the corner (to get on top the car in front of me because the passing zone is just after 3B) the brakes will lock up right at the very end when I am ready to lift off the brake pedal and get on the gas.

I am running faster now than previous years but I have run this car at Pacific Raceway for three years without this issue. I have GT3 end links and control arms, sway bars, JIC Coilovers with R compound tires, cup brake ducts etc. I am not looking to stop any faster, I just want them to not lock up. Has anyone else had this happen?

On a side note, I have access to some like new turbo red brake calipers that I can use to swap out for the next track day. I am going to try this to eliminate one set of variables. I am thinking that if one of the pistons is sticking for any reason, it may be causing this issue.

Thanks in advance if you can help!

adam_

Just an FYI- I seem to recall a handful of other reports about idiosyncratic ABS actuation in track situations... try a search here or on 6speed.

A

PS There's a word I've never seen on a car forum...

LVDell

Confused on this one. I didn't realize the brakes would lock. I thought ABS prevented that. Maybe a PSM anomaly?

adam_

Hows this..familiar?

http://www.6speedonline.com/forums/9...96-turbos.html

I knew I had read it somewhere....

Keep us posted

A

Macster

Not sure if this is source of your problem but with the Turbo (with cars with PSM) after the brakes are bled as usual the system must be bled some more using the PST2 connected the car with the ignition on and using the PST2 to turn on the booster pump and the system is bled from the front right bleeder valve. Bleed until clear bubble free fluid emerges.

While the bleeking process is going on fully depress (pump) the brake pedal as far as the stop at least 10 times.

Close the right front bleeder valve then immediately press the Stop button on the System Tester to end the pump's operation.

Switch off the ignition and disconnect the System Tester.

Top up the brake fluid level if necessary.

Sincerely,

Macster.

krambulle

Sorry I borrow the thread just to ask:

Is the ABS possible to 'turn off' in any easy way?

//Johan

adam_

Did you read the link I posted??? Instructions for disabling the ABS pump

krambulle

Nope, I didn't!

But I did now! Thanks!

//Johan

gbhstrat

I read the posts that were referenced to me on 6speed. It sounds just like the same problem I have. I installed a different set of factory red calipers over the weekend. I talked to Collin Cantrell who works on a lot of cup cars and he mentioned that a when brake pads get to worn, the pistons can get pushed too far out of the calipers and when under extreme heat and track conditions, they will start “wobbling” slightly within the caliper and permanently screw up the caliper. This will cause sticking and may be the source of the problem. This may be the source of the issue because the last track day before my car started this issue, I tag teamed my car with my son and this took my brake pads down to nothing. My pads on the front were paper thin by the end of the day. The posts on 6speed that I read contradict this theory because this issue occurred even after changing to bigger calipers. I will post what happens next week after my Wednesday track day.

adam_

Reading those posts it seems clear that this is a weird 'at the limits' issue that arises with the 996TT ABS system....

Keep us posted- you can see from 6speed that it is the collective input from many that can give us progress on this stuff.

tvurt

I believe that you can disable the PSM while leaving the ABS intact, and It "solves" this issue. You pull one relay, and it is disabled, with no other side effects besides a CEL.

Tom

gbhstrat

Do you know the specific relay I need to disconnect? I searched the site for “PSM disconnect" and went through several threads. I found that there are 3 relays that are related to PSM but I could not find info on the one that allows PSM to stay on but not connected to PSM. Note that I keep my PSM turned bitton off most of the time, if the track is wet then I keep PSM on to help me not get to out of shape.

tvurt

BBI was talking about making a resister and switch for disabling this. Here is the best info.

Tom


http://www.6speedonline.com/forums/9...ack-issue.html

Land Jet

Here is the PSM disconnect point under the master cylinder in the front trunk. It leaves ABS working.

gbhstrat

Thanks! This is good stuff. Now I can test the new brake calipers and if I still have the issue, I can also disconnect the PSM knowing this. I will be running with a small group at the track with long run times on Tuesday so I should have a report back next week. Also, on a side note, I love my Coleman rotors, I am starting my second season on the same rotors and they are still looking good. I have about 1000 miles of track time on them.