Faulty Abs (activating at low speeds, brake + abs lights)

[Lyle]

Originally Posted by mileshawk56

Not perhaps helpful from the diagnose scenario but if it reveals a faulty ABS pump and you are lucky and your car has no traction control fitted the price of a replacement unit is about £150.00 if you have traction control they are £1000.00 or £900.00. Chris S.

Well that is good news at least, although, still £150 plus labour I'd rather not spend if not required. I don't believe I have traction control but is there any way to tell for sure other than a button in my centre console? I have a zt which has had a wooden dash from a 75 swapped in at some point so have buttons for cruise control and heated seats etc which I know I don't have so wouldn't want to go on the presence of a button alone.

[Lyle]

Originally Posted by Mike Noc

I've sorted a fair few of these phantom ABS coming on at slow speeds, and none of them were due to a faulty ABS modulator.

Worn magnetic reluctors, a bit of rust behind a rear sensor lifting it away from the reluctor, cheap Ebay sensors switching at double the voltage they should and failing old sensors, but never the modulator. As long as the plug pins are in good condition I think it is rare for them to fail.

Yes I was also told this was a rare failure point. Thats an interesting point about the rust behind the sensors, would this show up when checking the wheel speeds matched or would you have no other indication than the phantom activation?

[Lyle]

Originally Posted by stevestrat

The T4 is specific to MGR vehicles and will show information that a generic diagnostic system may not. The problem would be finding a T4 system near you, the nearest I know of is Dreadnaught up in Callander.

PS Although he doesn't have a T4 I'd have a word with Dunc (Cossie Dunc), he has a garage out in Whitburn. Trader on here and a bl00dy good mechanic.

Yeah, I was quite surprised when I went on the forum T4 map that there was nobody in Glasgow. I've generally found that whatever you require is in this city somewhere. Would have thought there would be an ex MGR dealership that would still have one but guess not.

I will give it a week and see whether the symptoms change any further and what additional suggestions come in and then perhaps reach out to those that you have suggested. I had thought looking for an ex MGR dealership who may have worked on more of these cars may be the best plan of attack for a tricky problem like this. Good to have recommendations from people on here as I'd be warry now that unknown garages could take advantage since they know my regular garage has been unable to fix it.

[vitesse]

Couple of good photos from Arctic showing the build-up of rust around the rear abs sensor. Might explain what we are on about https://the75andztclub.co.uk/forum/s...=282109&page=2

Hope someone local with Toaf can help if you can't find a T4.

Good luck

Ps DMGRS have a very good deal on complete backplates

[Lyle]

Originally Posted by vitesse

Couple of good photos from Arctic showing the build-up of rust around the rear abs sensor. Might explain what we are on about https://the75andztclub.co.uk/forum/s...=282109&page=2

Hope someone local with Toaf can help if you can't find a T4.

Good luck

Ps DMGRS have a very good deal on complete backplates

Thanks for that, see what you mean now. Always scares me a bit with cars how you can have pockets of bad rust like that completely hidden from view.

The thread in general seems like a very similar problem albeit resolved by chance.

[Mike Noc]

Originally Posted by stevestrat

The T4 is specific to MGR vehicles and will show information that a generic diagnostic system may not. The problem would be finding a T4 system near you, the nearest I know of is Dreadnaught up in Callander.

PS Although he doesn't have a T4 I'd have a word with Dunc (Cossie Dunc), he has a garage out in Whitburn. Trader on here and a bl00dy good mechanic.

The problem is that the ABS system determines the rate of wheel acceleration and deceleration from the sensors picking up the magnetic reluctor segments on each wheel, so the odd missing segment may not flag up as an alarm, it is interpreted as a drop in speed. If there is a pattern to it then you may get a plausibility fault as the system doesn't see a fault, but does see something out of the normally expected results.

Originally Posted by Lyle

Thats an interesting point about the rust behind the sensors, would this show up when checking the wheel speeds matched or would you have no other indication than the phantom activation?

It depends on how much of a problem it has become - you may see a blip on the wheel speeds on diagnostics, but then again in the early stages with just the odd random missed segment you may not.

So for me a voltmeter and a bit of time spent checking each wheel in turn is preferred, and has so far got to the bottom of all the faults.

The rear ABS sensor that had a bit of rust behind the mounting point was difficult to spot, but was enough to increase the air gap slightly and cause the odd miss read.





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[Mike Noc]

Originally Posted by vitesse

Couple of good photos from Arctic showing the build-up of rust around the rear abs sensor. Might explain what we are on about https://the75andztclub.co.uk/forum/s...=282109&page=2

Hope someone local with Toaf can help if you can't find a T4.

Good luck

Ps DMGRS have a very good deal on complete backplates

That's different to the problem I had, although I have had rust from the back plate wear the magnetic reluctor as well.

Where the rear sensor is bolted on to the back plate there was some rust lifting the sensor away, increasing the air gap until the odd reluctor segment was missed.