Hi,
Whilst doing a front disc and pad change to eliminate what I thought was a slight warped disc condition, I think that I may have damaged the ABS valve block and I would appreciate any thoughts.
Stupidly, I forgot to undo the bleed nipple and gently pushed the pistons back 3-4 mm to allow for the new pads.
I noticed that one of the ABS wheel speed sensor earths was broken where the crimped connector is sandwiched at the bracket between the flexible brake hose and the rigid line. I re-crimped it and soldered it to the best of my ability.
When I went for a test drive I noticed the ABS and TRAC warning lights on.
When I turned off the ignition and restarted again the lights were off.
Braking gently at low speeds to bed the pads in, I felt a low speed shudder as if the discs were warped. Braking from higher speeds caused the car to really shake.
I fitted TRW discs and pads. The pads have chamfered leading and trailing edges, so the contact area is reduced by 10-15% compared to the Mintex pads that I removed.
I removed and refitted everything again and the discs run true.
Do you think the heavy shuddering is caused by a damaged ABS valve block or something simple like the pistons sticking due to the fact they are fully retracted, or the chamfered pads needing more bed in time?
Luckily, I have a spares car with a valve body.
Is there anything special I need to do when swopping them over except for bleeding all the brakes?
Any advice kindly appreciated. Many thanks, Philippe

 

Is the abs valve block the part with the abs module attached in the engine compartment? If so, you did not damage it. If you caused an internal break in the abs connecting cable you will get the abs light, and they do get brittle with age.
Do you still have a shudder, or is everything okay now?

 

I still have a very prominent shudder, but I have not changed the ABS valve body yet. Yes it is the part in the engine compartment.
Strangely enough the shudder gets worse after the car has been driven a few kilometres.
Thank you for your input.

 

The pads are fine. Chamfered edges won't cause this problem.

I find it interesting that the shudder came with the new discs? Unfortunately brand new discs can be warped too, so that could be the case here. In that case you should be able to get them replaced free of charge, if you contact the seller quickly.

You can try touching the front wheels after a short drive. If they are the same temperature, the brakes should be ok. One wheel being hotter than the other mean that one caliper is hanging, which could be the cause of the shudder.

Perhaps some dirt got trapped between the wheels and the rotors, or underneath the rotors on the mating surface? Make sure everything is 100% clean by using a wire brush.

 

I would suspect the electrical work on that earth lead.

 

That earth lead seems to be rather surplus to requirement, as discussed here recently. One of my rear sensors had the crimped connector broken from the wire completely, with no warning lights or malfunction of the ABS. I think it's just a "belt and braces" situation, as the wheel speed sensor earths itself in the hub anyway. I reconnected it and cleaned everything up, with no difference at all. I was doing rear shocks at the time and only came across it by accident.


I'd imagine the discs/pads are just bedding themselves in, but it might be worth checking that the anti rattle spring clips are firmly in place.


Failing that, check that the pads and discs are clean and grease free. Also, if you want to avoid undoing bleed nipples that can become corroded and tight, just remove the fluid filler cap to allow pressure/ fluid to flow back and escape. Just keep an eye on it so that it doesn't overflow. FWIW, if you have cruise control fitted, this won't work if your ABS isn't working.

 

+1 sogood. I had a broken ground ground wire on a front wheel with no effect. The fact that he had a shudder before replacing the rotors and has one now is confusing. But I would also suspect a warped rotor.

 

Maybe that's the case with Trac control. I have ABS only, no TRAC control, and drove around the better part of 2 yrs with the ABS fault due to the motor pins needing to be soldered on the board - Cruise control worked fabulously before and after I mended the ABS Module.

 

You may well be right, I am speaking from a fuzzy memory! There does seem to be links between Trac Control, ABS and Cruise Control. The electrics on these cars is certainly a minefield!

 

The shuddering at low speed feels like warped discs, but maybe it is the ABS valve block pulsing the pressure off and on?
The new discs are perfectly true. With the caliper and road wheel removed and the disc held tight to the hub with a couple of wheel nuts it is easy to spin the disc and check it against the caliper mounting bracket.
I have ordered a couple of new earth straps and will update once they have been fitted.
My fear that I have damaged the ABS valve block comes from here:
Replacing brake pads on an ABS car - Antilock brakes

The fact the ABS and TRAC warning lights came on after a simple "disc and pad change" leaves me worried.
Thanks for all the input and advice to date.
Philippe

 

I think the jagbits article is referring to contaminates and moisture causing damage. You should flush the brake system when you are done. If the abs system were pulsing, the light should be on.