ABS Brakes Issue

[Poosemon]

Hi,

Currently experiencing an issue with the brakes on my 1999 Puma (Front Discs, Rear Drums). Car is standard so no mods to the brakes/altering the sizes of the discs.

Recently the car has started braking with odd effects including;

-Occasionally the ABS firing violently when breaking at mid->low speed, the more violent effects when the car is almost at a stop
-Wheel Wobble when braking from high->speed, gets better once at a lower speed, or if braking with little force
-Occasional odd sound like a groaning & crunching when driving along (this is stopped by a brief tap on the brakes)

It has suggested this could be an ABS pump issue, but was wondering if anyone else has any suggestions before I pursue this.

One thing to note is during all of this the ABS and TCS lights do not light up (they do light up and go out as normal during start up)

Thank you in advance for any tips

 

[zinc2000]

Could be warped/cracked disc, damaged abs sensor ring, worn/damaged pads
I take it by "ABS firing violently" you mean you can feel it through the pedal?

Personally I would check the easy bits first, pull the wheels of and check pads, discs for damage, check ABS sensor ring behind disc as well, also check all the suspension components as well while you have the wheels off oh and make sure the wheels themselves are not damaged

 

[Poosemon]

Thanks, r.e the ABS sensor ring. If this is damaged am i right in saying that it is part of the wheel bearing assembly so if it needs changing both items will need to be done. Discs and Pads can sort out myself, however bearing requires the attention of a garage as dont have the tools....

 

[zinc2000]

Aye, think the sensor ring is along with the hub, you have to remove hub etc to remove the ring.

Fingers crossed checking/renewing rest of the stuff will cure the problem without

 

[Wild E. Coyote]

My bet would be a seized brake caliper piston. The dust seal must have come off and the dust is entering the space between piston and caliper and the piston is now seized in outward position.
Second line of thought would be a really bad wheel bearing and the wheel having axial runout. That would alter the gap between sensor and tone ring. When the ring is to far away, sensor can't pick up the signal and ABS unit would think the wheel has stopped and go into action. That would explain your description of random ABS triggering.
The tone ring on his own might get corroded, but I have never seen one desintegrated.

Mind you: the ABS sensors will be impossible to remove from the hub. If they are ok (test with Ohmmeter should return values of aprox 1100 Ohms) no need to touch them at all

 

[Poosemon]

Turned out the abs detection ring was damaged which was causing it to read incorrectly and fire the abs and display strange behaviour, coupled with a failing wheel bearing.

All replaced and working however there is still a definite judder which gets worse when the brakes are hot (i.e if using them a few times in short sucssesion), however nowhere near the problems i was having before.

Going to need to get the discs and pads replaced (annoying as only did them 1000miles ago) but think the failing bearing and abs firing when not required has probably overheated the discs at some point and caused them to warp.