Recently had problems with the ABS light coming on frequently and the low-speed brake pedal vibration (as in an ABS-assisted stop). Speedometer was also acting up with drops in displayed speed especially below 40 mhp. After cleaning front reluctors and sensors problem remained and seemed to get worse quickly. Discovered that rear differential housing holds the third ABS sensor along with the speedometer sensor as one unit. Removed sensor from housing (very easy) and cleaned off metal particles on sensor. Also discovered that one wire into the sensor connection was broken inside the insulation (a gentle pull broke the insulation at the internal wire break). Soldered wire together again and sealed with heatshrink. This solved the problem with both speedometer and ABS warning. Usually we see problems with the front ABS sensors but dont forget the rear unit, especially if your speedometer and ANY inconsistency in displaying speed.

1990 740 turbo w/236k, 2000 V70 w/50k