ABS fault causing caliper to be stuck

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Oliver53
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Joined: 06 Nov 2012, 20:59

ABS fault causing caliper to be stuck

Post by 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
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Re: ABS fault causing caliper to be stuck

Post by 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.
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xantia_v6
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Re: ABS fault causing caliper to be stuck

Post by xantia_v6 »

The disk, pads and caliper should withstand that much heat without permanent damage. It is what they are designed to do.
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Oliver53
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Re: ABS fault causing caliper to be stuck

Post by Oliver53 »

Gibbo2286 wrote:
25 Sep 2021, 16:10
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.
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Oliver53
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Re: ABS fault causing caliper to be stuck

Post by Oliver53 »

xantia_v6 wrote:
25 Sep 2021, 21:00
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.
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GiveMeABreak
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Re: ABS fault causing caliper to be stuck

Post by 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.