ABS fault causing caliper to be stuck

[Oliver53]

Hi guys, I've got a MK1 C5 HDI and it's been a reliable workhorse for over two years. Last week when we were cruising on the motorway the ABS light, hand brake light suddenly went on and on the dash it displayed "ABS fault" and "STOP" with warning sounds. The brakes worked fine and no loss of brake fluid or anything abnormal otherwise. Continued driving and arrived at home without any drama dispite the scary warnings.

Checked with Lexia and the fault was "Permanent Fault - electrovalve internal". Wheel speed sensor readings were fine so I guess it's indeed the ABS pump failed. Went for a short drive with a few times of hard braking hoping it could somehow return a sticky electrovalve back to normal, but it didn't work. On the way home I felt slight decrease in power. Continued driving for one mile back home. Then I saw a dark red front left disc and it smoked a little bit. Obviously the front left caliper was stuck somehow.

Ordered a ABS pump of the same model number off ebay and fitted it. Programmed with Lexia (the only thing needed change was the tyre size actually), Bled the primary circuit, then the brakes worked fine and no faults or warnings any more. The disc is not obviously warping, and no noises when braking. No leaks. I drove the car for a while and checked temperature of the front discs, the left one (which was glowing red before as mentioned above) was always about 20 degC higher than the right one, for example, 80C vs 60C, 130C vs 110C, etc. But nothing more serious than that.

I have a few questions please:

1. My guess is that the faulty ABS pump which had a stuck electrovalve caused the front left caliper to be stuck, as a result, the disc turned glowing red. Has anyone experienced this before? Or anyone has a different theory?

2. I was thinking about renewing the front left caliper (because I am not sure if it was damaged by the heat when disc was glowing red), the disc and pads. But they all seem to be working just fine now, do you think it's necessary to replace the lot?

3. I only bled the primary circuit, and didn't do the Lexia bleeding for the ABS as I don't have a pressure tool and I am not sure how I should do it as the precedure required "open both front bleeding valves". I suppose if I open both valves, it'll be hard to stop air getting into one of them. But I am inexperienced in this topic. As the pedals are firm so far it seems, should I try to bleed the ABS anyway?


Many thanks for any suggestions.


Oliver

[Gibbo2286]

A common fault on those callipers is the handbrake lever not returning to the stop due to lack of lubrication, check that first before getting in too deep with expensive stuff.

[xantia_v6]

The disk, pads and caliper should withstand that much heat without permanent damage. It is what they are designed to do.

[Oliver53]

A common fault on those callipers is the handbrake lever not returning to the stop due to lack of lubrication, check that first before getting in too deep with expensive stuff.

Thanks. The handbrake lever was found sticky last year at MOT. I used some penetrating oil and freed it up and since then it worked OK as far as I can tell.

[Oliver53]

The disk, pads and caliper should withstand that much heat without permanent damage. It is what they are designed to do.

Thanks! That's reassuring.

[GiveMeABreak]

It is part of the main operation when bleeding to also bleed the secondary ABS circuit as you can still have air in the system.

[aspire_helen]

Thought I would add my experience re over-heating front brakes on my 2001 C5 Mk1. Some years ago (at around 150K miles) it became apparent the front right brake was binding. The calliper was stuck in the carrier. An easy fix to de-rust the carrier. The following year I noticed some mild knocking coming from the front brakes under moderate to hard braking. This is what I found on the drivers side front.
1. One carrier was slightly loose, but its bolts were fully torqued. The cause was poor design. The bracket holding the air deflector is retained by the 2 hub/carrier bolts such that the bracket acts as a spacer between the hub and carrier. The bracket had rusted away leaving a gap, allowing the carrier to move.
2. The guide pins were seized in their bores - completely dry and rusted.
3. One of the inner pads had partially de-laminated, ie become unstuck from the metal backing plate (APEC brand).
It is possible that the heat from the binding brakes had contributed. Hence, I would recommend completely over-hauling any brake that has experienced significant overheating, looking for heat damage to lubrication, seals (piston, pins) etc.