rears locking - track

aftermath · aftermath's Garage

Im locking the rears easily on the track, I have to be real easy applying pressure to not transfer too much to the fronts too fast, then I can control the locking, however Im getting passed in the braking zones. I guess everyone figured out I brake early ! I can hear the rears chirping on the bumps on the back straight and the other drivers are telling me Im puffing smoke from the rears on the front straight.

83 - 944 with 951 brakes. But pushing 390hp. I didnt have this problem at lapping sessions on a smaller track, I did have a alignment done since. They took out some toe and camber in the rears. Its it my driving, do I have a brake problem, do I have a alignment issue? Its a bit squirly under braking, but not too bad. Ive only had the car out 3 times so Im still learning, but threshold braking on this car requires me to brake way earlier than the cars around me. Im on 255/40/17 street tires for now.

The highlight of my weekend was passing a gt3 in the corners !

many944s · 06-02-2009, 04:02 AM

-What pad composition(s)/ combination are you running?

-What fluid are you using?

-When was the system bled/ fluid changed?

-What rotors are you using in the rear? Slotted, drilled, D&S?

Need a little bit more info.
-Nick

924RACR · 06-02-2009, 04:18 AM

Hmmm... 951 brakes, huh? Did you change the master cylinder too?

aftermath · aftermath's Garage

Its got a ls1 converstion so the previous owner put in a hydra boost for a brake system. As far as I can tell its the newer style of 951 brakes. I got my ate blue delivered last week I ran out of time to bleed the system, I will be doing that this week. Im going to try that first. The rotors are solid, not drilled or slotted. When it was in for an alignment last week I had them measure the pads to make sure they were still good ( again out of time to do it myself ) maybe the tech let some air in getting the pads in\out. Im only guessing here. I figure bleed the brakes, if that doesn solve the problem then I can try mixing pads. I got my pressure bleeder from pelican 2 weeks ago and it should make it real easy. Or maybe the hydraboost if starting to fail in the fronts. I can still brake, but Im guessing im at 80% of what the cars braking potential is. I dont know what pads are in the car, only that there is a lot of wear left on them. I was going to order the Hawk Blue, but Im going to try one more track weekend after bleeding the system.

PS: Its pretty powerfull if I can run with a gt3 down the straights. I need to start removing more stuff ( windows, motors, door panels, heater motor ) and put some r compound tires on it. Ive got a tire place as a sponsor, going with the Nitto NT01 255/40/17.

924RACR · 06-02-2009, 06:07 AM

Oh, yeah, duh, that car... the one I test drove.

One possibility, and I don't remember the setup on that car, but if he swapped in not only the booster but also the MC, then the sizing might be wrong. Good news is, easily fixed with an adjustable prop valve! Perfectly appropriate for a track car.

By all means do the checks you had planned, but it may just have a little too much rear brake.

A photo of the brake MC might help identify it, see if it looks right (stock 944 or 951)...

aftermath · aftermath's Garage

924Racr, yep that car. It developed a engine knock last fall at lapping days, I had a crank bearing fail but you could see oiling issues causing damage on the other bearings. It wasnt too much damage as I pulled off the track right away, but the dam engine takes $1200 in torque to yield bolts to rebuild. We changed the cam and valve train during the rebuild and I added a accusump, its good to 6900rpm from 6200 now ( Ive still got the rev limiter set to 6200 ). I bought a programmer for it to deal with the new cam, Ive got the fuel enrichment up 10% and left the timing. First is brakes and suspension. Once I have that sorted out and get consistent in the car I will look for more power, for now its fast enough. The engine guy I bought the parts from figures Im now running about 390 at the crank. I can get more with air flow and intake later.

944 boy · 06-02-2009, 06:45 AM

When you put the brakes on did you include the brake bias valve? It screws in the master cyl. then the hard line screws into that. It cuts the pressure to the rear brakes.

aftermath · aftermath's Garage

944 boy I dont know what the previous owner did. But my brake issue is at the top of my list, I doubt a bias valve was installed. I didnt do the brake upgrade. But now Im asking what can I do, I will start with bleeding the system. Im thinking no matter what I will end up with a valve, I dont know whats the best\reasonably priced option.