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Old 06-28-2002, 05:27 PM
Joseph Bauers
Posts: n/a
ABS mystery, or learning what the BS in ABS means!

I have a 1989 300SE. Recently,I had the MB dealer install new ball joints and body strut bushings. After picking up the car,I noticed that the brakes were exhibiting a strange problem. The car would brake normally until it came to a stop, at which point I would feel a pulsing in the pedal briefly, as if the ABS had been activated for a second or so.

My MB tech friend said that this symptom was most likely caused by bad wheel speed sensors. He said he had never changed ABS pumps except in the case of cars that had been in accidents. Other cars showing the same symptoms as mine had been cured with a change of sensors.

I ordered the sensors and installed them myself. When I got the car back on the road, I noticed no improvement. Another tech suggested that perhaps the splines on the hub were dirty--he said that grease or other things getting between splines would cause the sensor to misread the wheel speed.
I removed the front rotors and discovered, indeed, that both hub splines had dirt and what appeared to be grease packed between some of the splines. The techs and I sprayed solvent on them,then dried them with compressed air.

When I reinstalled the rotors and tires,the brakes behaved normally for many applications--perhaps 12 or more. Then, the problem intermittently reappeared, though not as pronounced as it had been initially. Now, I would say that I experience a small pulsing about 40% of the time.
My tech friend suggested disconnecting the battery for a minute,then reconnecting it, hoping that the ABS would reset its codes. This did no good.

He also said that there is a third sensor on the rear differential. He said I might consider pulling it and cleaning it, but he cautioned me that these often were difficult to remove and there was a danger I might break it off in the rear differential. As of yet, I have not looked into the rear sensor.

I am to the point where I am seriously considering unplugging the ABS pump altogether.

Anyone with experience or thoughts on this problem?

Joe Bauers
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