ABS vibration in pedal at very low speed

[rwtags]

I seem to be having a problem with my ABS system, at very low speeds <10mph when coming to a full stop sometimes the brake pedal seems to vibrate, such as ABS vibrations not rotor wobble etc.

I am not sure how to diagnose it, sometimes the ABS light will come on, but very rarely, once every 100 miles or so? something around that range.
Could this be a speed sensor?

[Kershaw]

Try unplugging the little black sensor that sits in front of the fuse box.

[nando]

yeah, sounds like the mercury switch could have gone bad or is shorting out.

IIRC a bad wheel sensor could also do this?

The good thing is the E30 ABS systems are extremely simple, the bad thing is they are old and new parts are expensive..

[AndrewBird]

Maybe the sensors are just dirty? They are magnetic so they pick up a lot of iron filings/debris. Pull them out and take a look.

[litu]

I had same issues, that abs relay was broken, that what sits above the abs ecus unit it he cabin, near streering colum

[rwtags]

Doing an examination, of every sensor wire, it wound up being the driver's sensor wire, was rubbing and wore wire down. The grommet was gone, so it was just metal on the wire, finally wore down. Replacement and it hasn't come back yet!

[rwtags]

Problem came back when my throttle cable got locked at around 1.5k drove home fine, and fixed that, but every time i stopped the ABS on the pedal was kicking me back, almost hit someone when i though i was stopped and i was rolling backwards, really had to lay on the brake more than i wanted it.

This mercury switch infront of the fuse box, can i just drill it out? and go to a junkyard and find one? is there a way to test it? if i drive around with it unplugged will the ABS light be on? I guess only one way to find out.

yeah, sounds like the mercury switch could have gone bad or is shorting out.

IIRC a bad wheel sensor could also do this?

The good thing is the E30 ABS systems are extremely simple, the bad thing is they are old and new parts are expensive..

[rahhusseini@hotmail.com]

If the problem of abs vibration still ,u must to look to the wiring of right passenger abs sensor if is very close to main coil wire then it be under magnetic field . u need to push away the abs wire from coil (hight tension) wire . beware of magnetic field near all abs wire on any location . I had this abs issue for maybe 7 year .and finaly solved 3month ago by this way and the abs became great. Good luck.