Oddjob

Paul,

I never had an ABS fault with my 89 Turbos on the street or track, and I did have Turbo Cup springs on one of them (so it was pretty stiff). But with my 87T track car, I have had various faults, always related to hitting bumps in the pavement at very high speed (probably 140+ at BIR between turn 1 and 2 - its a pretty rough track, not like Road America or other well maintained courses), or hitting the rumble strips on track-out. I believe I do have a problem with an ABS wheel sensor on that car, but if you talk to club racers with late model 944s (with ABS), there is somewhat of a chronic problem with the ABS occasionally faulting out.

Yes, I believe that the main or original intension of the ABS switch on the Cups was as a shutoff, for drivers that didnt like it or trust it (since it was new technology back in '87). But going through some of the documentation that you sent me (the notes from Weissach to PMNA, and from Freund to Seabolt) there are several notes relating to the ABS function, and there are some implied problems.



" - there is an off/on switch for the funktion of the ABS on the center-panel."

" - watch the standard warning light when the ABS is in funktion - it lights up when there is a failure / just like in the standard 944 Turbo."

"We did have problems during the cup races, the drivers complained a hard pedal, the ABS works and there is no increasing deceleration. This is the normal funktion of the ABS when one wheel is jumping and locking up while in the air for a short moment."

"There also have been failures of the system, the control-lamp did go on and there was no more funktion. When you turn the ignition on again everything was ok. The reason is not enough free play between the sensor and the toothed wheel due to high elastic deformation of the suspension under hight lateral acceleration. Check the gap (max 1.3mm) with a feeler gage or the ABS-testgage (rear axle)."

"For the switch for the ABS you can use any off-on switch that is on the market. We dont have them any more and we would have to order them."



The note on the max. gap between the rear wheel ABS sensor and the ABS pickup ring on the hub, somewhat explains the issue that many of us racers have run into. There is enough flex in the suspension and in the wheel bearings (when heavily stressed with high spring rates, stiff tire side walls, and race conditions), that the gap between the sensor and ring changes enough that the ECU does not pick up a solid signal from the sensor, so it faults out.

And yes, turning off the ignition, or shutting off the ABS switch (both cut all power to the ABS ECU) does clear the fault memory of the ECU and it resets it. A lot of guys now refer to the switch as an ABS reset switch, not a Shut-off switch (because, like Eric and I, they always prefer to run with the ABS on).