ABS is really sensitive. 1987 190d 2.5 Turbo

[benhogan]

I have started driving my 190d and the first thing I noticed is the ABS brakes tend to come on really easily.

If I come to a regular stop it is fine. However, when there is a little bit of gravel or if I come to stop at a bottom of a hill, the ABS brakes pulse.

My hypothesis is the ABS wheel sensors are just dirty perhaps. My other guess is that some of the flexible brake lines are constricted (swollen) which is causing one or more wheels to turn at a different speed than the others causing the ABS to come on.

Any tips as to where to start? Maybe a brake fluid change (it looks fine though color-wise). This is the weekend project.

[winmutt]

It is possible that the ridges on the hub are filled with road debris and throwing off the reading. Maybe its just meant to be sensitive. My 87 is the same way.

[nhdoc]

Make sure your tires are in good shape too. If the ABS is activating under light braking it is because one or more of the wheels is skidding. You also might have a seized caliper on one side making the other work harder and locking up. So, I would first look at the tires and then make sure every wheel has braking power.

[Jeremy5848]

Agreed. Remove and clean the wheel sensors and also check the "gear" that creates the pulses. The ones on my '87 were quite dirty. Also make sure your tires are the same size. Check the wires from the ABS sensors up into the engine compartment and make sure the wires are in good condition.

Finally, when the ignition is first turned on and the engine is started, the ABS controller goes through a self check. When you start driving and make your first stop, ABS pulses the brakes just to make sure. If something happens to cause an electrical interruption to the power to the ABS controller, it will happen again and again. However, you would also be seeing the ABS light come on for a couple of seconds each time that happens.

Jeremy

[josha37]

My vote is for a over-excited brake at one of the corners (failed caliper, slide, adjusted incorrectly, failed porportioning valve, etc) causing one tire to skid (thank your benz for being so quiet).

[winmutt]

Originally Posted by Jeremy5848

Finally, when the ignition is first turned on and the engine is started, the ABS controller goes through a self check. When you start driving and make your first stop, ABS pulses the brakes just to make sure. I

That is a very interesting tidbit!

[sjh]

Originally Posted by Jeremy5848

Finally, when the ignition is first turned on and the engine is started, the ABS controller goes through a self check. When you start driving and make your first stop, ABS pulses the brakes just to make sure....However, you would also be seeing the ABS light come on for a couple of seconds each time that happens.

Jeremy

Does that mean I should feel a sense through the brake pedal and my dash ABS light should flash the first time I apply the brakes? I've never observed that.

[bustedbenz]

Mine has never done that self test either. If it is pulsing the pedal on the first brake, I've never felt it.

Come to think of it, my anti-lock light illuminates when I turn the switch on but I've never seen it come on when the brakes activated. I've felt the pedal pulse many times but never has the light illuminated.

[compu_85]

The ABS light only comes on when there is a fault. The system does a self test when you pass 7 MPH, not when you press the brakes the first time.

-J

[Murkybenz]

It can also be old glazed pads that cause it.

[sjh]

Originally Posted by compu_85

The ABS light only comes on when there is a fault. The system does a self test when you pass 7 MPH, not when you press the brakes the first time.

-J

Thanks.

Are there any indications that the driver would sense?

[compu_85]

I never noticed any. On my dad's Passat, which has a much newer Bosh ABS system you can feel the system click when you start moving (or perhaps it's something in the AWD?), but on the old 2E system our cars have I've never felt anything physical when the self check occurs.

-J

[benhogan]

I guess I will clean the ABS sensors at the wheels this weekend and check for stuck calipers.

As usual, thanks for all the input guys.

You rock.