I have a 90 4 matic that has had some issues with it's abs /4 matic system.
Recently i had the vehicle working , abs was acting up somewhat but was in other words working.
MY sypmtoms at the time were abs PULSING at low speed and seemingly slow stop times.I had also a binding in the 4 matic when i turned sharpley to the right at low speed. During last winter I had a suxpension/ right rear control arm / body mount failiure. My mechanic finally repaired the frame and suspension.
In doing so he removed the axles and found the ring gear for the abs speed sensor to be extremely corroded . He then proceeded to clean the rust off the gear/abs sensor and now I have my abs/ traction light come on all the time.!!!
My mechanic attempted to diagnose the problem and has begun with a overhaul of my Physical Brake items ( ie pads , calipers / rotors/ replacement of brake fluid.) making sure that all was in working order .
Upon all work done , still symptoms persist.
we then looked into the 4 matic / abs control units .
we did not have the correcty replacement parts but he had a spare abs unit from a 300e non 4matic .we installed and abs light still on and traction light is out . I do not think this fixed the symptoms .At least the front wheels are not binding. the car is drivable.
still slow to stop.
My recent correspondance with a fellow 4 matic owner / mb tech . He informed me that ;since cleaning the ring gear, there is too large a gap between the wheel speed sensors and the ring gear on the axles. he suggest grinding down the mounting area of the speed sensors surface down a mm or so , this will bring the gear and sensor closer .I am hoping i am not looking at replacing the abs control unit, He says there is ways of testing this issue.
I beleive that he may be on to somehting as if the speed sensoers not reading correctly it would seem like they would be slipping thus making my traction control come on and make my 4 matic engage fully. thus making the turnng symptoms and abs symptoms sound accurate.
I have too much money in this project to quit but I am at wits end. HELP!!
previously ;
I have replaced a speed sensor and noticed the abs cable pre connector was exposed and corroded in an area near the fuse panel . I spliced the wires and re soldered them back .After doing so l had my abs sysem and 4 matic systems working. last winter she handled snow and ice very well , until we had the suspensoin failure. and repair.
Since i have been unable to get the abs to work properly. Any advice and info ( not geared towards me selling this money pit) will be beneficial.

The 4 channel ABS on that car is UN-like any other 300E"s system. So the 3 channel systems computer won't work.

Start by measuring the OUTPUT signal from all 4 wheel speed sensors. Using a SCOPE is the best method.

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For those inclined , here is an interesting Tech article on low speed ABS pulsing..
Well written and a good site for their other articles..............

http://www.picotech.com/auto/articles/diagnosing-abs.html

1988 300e 4matic When Abs Acts Up Lots Of Pedal No Stopping Power What So Ever.push Right Threw Floor.no Stop