ABS Compatibility

[willum]

Hi All

Still trying to cure (on a tight budget) the annoying "patting under the foot as you come to a stop" from my W124. Seems quite probable it's a wheel sensor on the way. :-(

Found a couple of dead Mercs in the local scrappy - 190s (C reg) and 230s. Does anyone know if the Wheels sensors (and any other ABS bits) are compatible?

Willum

 

[wireman]

The ABS does not have any function at low speeds <5mph or so.
Are the front/rear disks inner and outer edges free of rust/corrosion?

 

[television]

I do not think that a warped disc would do it, and I cant think of any servo fault either

 

[willum]

aahhh

The "patting under the foot" syndrome is definitely the ABS kicking. You can hear it as well. Only happens at very low speed, probably less than 5mph (I'll check). In addition, the ABS works unless I exceed 70ish mph, then the fail light comes on and the ABS switches off, resetting to normal if the ignition is cycled.

Much rust/gunge cleaned out of the hub area but the problem persists.

I know I could take the old girl to a dealer for a check but any bills like that will rapidly exceed the value of the car, hence the DIY/scrappy/are 190/230 bits compatible approach.

Willum

 

[television]

Have you checked the OVP relay

 

[willum]

short answer ... not personally but was told all looked fine (a month ago) when it was inspected in relation to an alternator problem.

I've recently found out what the OVP is - I think you told me - so I'll dig back through the threads and check it for myself

Ta

Willum

 

[wireman]

Acording to my owners mannual the ABS does nothing at speeds less than 5 ish mph. The system must have a low speed cut out otherwise the vehicle could never be brought to a halt whilst maneuvering on steering lock without the ABS joining in and playing up ( my 124's ABS can be persuaded to give a kick if I am less than gentle with the speed whilst reverse parking).

The fault occuring at high and low speeds suggests sensor problems.
The sensors on the front are associated with a phonic wheel affixed to each front hub behind the disk, rust on these may be a source of trouble, the ABS computer (behind the battery) may be getting rogue pulses which are confusing it. The computer compares wheel speeds and sets valves in the pump to hold fluid in the cylinders for slight speed unballance or pump fluid back up the brake lines for larger unballance.
The rear sensor is in the nose of the diff on the prop shaft.
The system fitted is Bosch ABS3 Three channel, two for the front one for the rear.

My first guess is that one of the front sensors ain't quite right, too much clearance or rusted teeth being common in this type of sensor.
The probe is a magnet with a coil around it and bits of crud can stick to the probe tip.

I do not know but think that the pump unit may be the same as other similar models and probably work OK, the controler will almost certainly have different characteristics to match the car and sensors fitted (and the number of teeth on the phonic wheels).

 

[willum]

Ta

going out to look at the propshaft end now....

Willum