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
bauersjo@soltec.net

MAKE SURE THAT THE NEW SENSORS ARE REINFORCED WHERE THEY ATTACH TO THE WIRE HOLDING BRACKETS. MERCEDES UPDATED THEM ALONG TIME AGO. THE REAR SENSOR USUALLY DOES NOT GO BAD BUT IT IS POSSIBLE. IT IS VERY EASY TO REPLACE. YOU CAN TEST THEM WITH AN OHM METER. WIGGLE THE WIRES WHILE TESTING TO SEE IF THERE IS AN OPEN.

As you know, there should not be grease on those ABS 'splines'.
It may have come through the hub seal if the seal was damaged, or if the hub was overpacked with grease.
Remove the sensor, shine a light in there, and see if new grease has deposited on the splines.

__________________
1986 300E 5-Speed 240k mi.

be aware that by disabling your ABS system, should you get into an accident, and should it be discovered that your ABS is not functioning, you could land yourself in a great deal of trouble.

At the very least, you're going to have to go through a great deal of time and money proving how the non functioning ABS was not the cause.

I'd be a little more of a hard-ass with your dealer and say that the trial and error approach is not acceptable if you have to keep replacing parts that are not the cause.

They should be diagnosing the problem...not guessing and making you buy parts ad nauseum without solving the problem. if they want to go the route otf trial and error, fine, but on THEIR time. THEY try it out and see if the problem is resolved. if it's not, put the original parts back in and proceed to the next possible cause.

Find another car, like yours, and see if you can swap out the ABS computer. See what the result is. if the car behaves normally, it's the computer. if it exhibits the same symptopms, it's something in the braking system. you have new front sensors and cleaned splines. all that's left are 1) rear sensor or 2) wiring.

__________________
'94 W124.036 249/040 leder; 8.25x17 EvoIIs
'93 W124.036 199/040 leder; 8.25x17 EvoIIs, up in flames...LITERALLY!
'93 W124.036 481/040 leder; euro delivery; 8.25x17 EvoIIs
'88 R107.048 441/409 leder; Euro lights
'87 W201.034 199/040 leder; Euro lights; EvoII brakes; 8x16 EvoIs - soon: 500E rear brakes
'70 R113.044 050/526; factory alloys; Euro lights

We learn about the Protein Manufacturing Project Report 2022 in this post. Knowing where to get wholesome foods for our bodies is a good thing. It's also true that there are a lot of data science services available on the market, however eBlick is far superior in my opinion. Visit Einblick's website at Einblick.ai and I hope you find this material beneficial.

sounds like typical front sensors to me, did a lot of 124s and 201s 20 yrs ago. maybe the chinese replacements are the issue, if they are not bosch, which was oe. had to replace 1 rear sensor in a 126. abs light on, no abs pedal dance during slow stops. had the bosch abs tool and found it quick. that was 20 yrs ago, also.

i'd had to scope the front sensors during braking to see if the signal is corrupted. never replaced any abs ecu or hyd. unit in any bosch abs car.

And this thread is 20 years old!!
Yesterday's post is a scam.

whoops, don't read too well. good catch.