Name: Sherman A. Johnson
Make: 2002 Impreza WRX
Mileage: Approx. 21,000 and 29,000
Time Out Of Use: N/A at this time
Problem and Likely Cause: ABS seems to be over-sensitive. It activates on smooth dry pavement and the brake pedal goes to the floor. Braking force is dramatically reduced. The cause is a mystery to me.
Modifications: Firestone SZ-50 tires (stock size). Hawk HP Plus pads with stock rotors. First instance was with Bridgestone RE 730's and stock brakes.
Submitted for Warranty Work: Yes.
Reason for Denial: No TSB from SOA. Problem hard to duplicate.
Story: I just wanted to clarify and update my post (above).
First of all, there seem to be two DIFFERENT ABS problems. The first, and most common, is early ABS activation on rough or uneven surfaces (railroad crossings, etc) and a resultant loss of braking force. While I have noticed that the ABS seems over-sensitive, I have not noticed a significant reduction in braking ability when it activates. With my WRX, it is possible to activate the ABS on almost any rough surface, but the pedal does not drop and the brakes still work.
There does seem to be an initial period of <1 sec. where the braking force is reduced but then the ABS seems to get itself sorted out. The pedal stays firm, with the typical ABS vibration.
Second, and less common, is the problem I had twice (and reported above). I experienced the same loss of braking force, but in both instances I was on SMOOTH, EVEN pavement. In both cases a driver cut in front of me (for no apparent reason) without warning (no signal) travelling at a much slower speed. In both instances I braked hard initially (with no problem) then let up on the pedal and braked hard again. In both instances it was on this _second_ application of the brakes that they essentially FAILED! I had just a fraction (maybe 1/4 - 1/3) of the normal decelleration. Luckily, in both cases I had somewhere to go (the shoulder or an empty lane).
Also, I've posted this elsewhere, but after the second instance of "mysterious brake force reduction" I bled my brakes and found a significant amount of air (not litttle bubbles, but LONG sections of the clear bleeder hose filled with air!) in the line when I was bleeding the right front! Up to that point, the brakes had not been touched (I got the car straight of the truck with 6 miles on it).
I now have over 45,000 miles and the problem has not reoccured. Of course, it was so intermittent to begin with that I don't really know if bleeding the brakes fixed the problem.
It would be interesting to know if anyone else finds air in the system when bleeding the brakes for the first time.
Finally, it was noted above, but it really is important that unresolved safety-related problems get reported to the NHTSA. Not only to help others, but to help ourselves as well. That may be the only way these ABS problems will get resolved.