75ZT Community

Hi folks, advice appreciated please - I think I have a failing rear wheel bearing causing an intermittent ABS (Antilock Braking System) issue. Fault codes 18 (wrong gear at one wheel) and 00 (unknown error) read by TOAF. Vibration at 70+ the past ~1500 miles and a droning at motorway speed (but boot trim and sound deadening under rear seat removed). Occasional rubbing noises. Very occasional noises cornering one way and different noise the other way past 300 miles (only happened 2-3 times). High pitched noise at times last time I drove it. No related advisory on MoT <100 miles ago. No play in any bearings 1500 miles ago.

ABS light came on intermittently last week (car not used every single day) after slight crunch whilst braking under 30mph and then tapping started from pedalbox, stopped when light came on, same again last time I drove it. Very occasional metallic tapping when braking and slowing down to a stop past ~1500? miles.

Noises sound like coming from N/S/R, just checked it - no play but wheel is a bit stiff and doesn't continue spinning if you spin it and let go. Handbrake correctly adjusted <1500 miles ago. O/S/R seems fine.

Could the bearing be seizing up? How do I know it's that not the calliper without removing the brake pads? Tempted to go ahead and replace the N/S/R bearing but any advice to confirm diagnosis very welcome! Thanks.

A common problem with the rears, is rust from the backplates getting onto the sensors or more often the magnetic rings in the bearing, and causing just the symptoms you are seeing with the ABS. Usual fix is a new hub and bearing, but vital to do a good cleanup. Also it isn't unknown for the diagnostics to detect the wrong wheel.

Most of the time when you get pulsing from the brake pedal as thought the ABS is kicking in on gravel, it turns out to be the OS rear bearing, personally for the cost of bearing i would change both, also check the back plate for corrosion, if corroded either change the back plates or clean and treat them with k-rust and paint then black after.

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Hopefully replacing the bearing will solve your problem, as said they are not expensive or too difficult. It may be as also mentioned the backplates have failed/rusted away and they also require replacement. Having just done both sides on mine these are a little more involved. The usual problem is the handbrake cable has become rusted in place as it goes through the back plate. I found the best way to get these out was to sacrifice the old backplate that has reached end of life. To do this you need to take an angle grinder to the tube that encapsulates the hand brake cable as it passes through the backplate and grind the side of it away until you reach the outer skin of the hand brake cable, this should then be loose enough for you to wrestle the cable out of the old backplate.

Thank you chaps - with the coincidental ABS issue I will hope that the stiff wheel is due to the bearing seizing and not a second issue with the calliper (I had the other rear calliper partly seize 2,000 miles ago).

I shall get a new bearing and see what it is like once stripped, I have a spare backplate if needed.

Any recommendations for a bearing? Are FAI decent enough as a reasonably priced replacement or should I perhaps go with what DMGRS stock?

Bolin wrote:Thank you chaps - with the coincidental ABS issue I will hope that the stiff wheel is due to the bearing seizing and not a second issue with the calliper (I had the other rear calliper partly seize 2,000 miles ago).

I shall get a new bearing and see what it is like once stripped, I have a spare backplate if needed.

Any recommendations for a bearing? Are FAI decent enough as a reasonably priced replacement or should I perhaps go with what DMGRS stock?

Go with the DMGRS ones because if it goes wrong within the 12 months they will send you another, other sellers may argue the toss with you.

I would strip and look before buying anything. While there are always exceptions wheel bearings don't tend to fail suddenly, nor do most bearings in my experience. They run for years just getting noisier and if the wheel is not rotating freely a common culprit on our cars is a failure of the backplate and/or handbrake shoes as a result.

Thanks folks. It (or something) has been failing since August at least, the vibration might have started earlier than that and it and the noises started before the MoT but I hadn't been able to feel anything when inspecting the car myself. Definitely got worse since the MoT and now not spinning freely so I'll strip it and see. Today I felt it and wheel and tyre are getting hot and there was a odd smell, bit like burning rubber. Hopefully it is all one problem, I'll find out when I remove the calliper, and disc if it still doesn't spin freely.

Many moons ago I had an event with a seized throttle cable approaching a 90 degree bend. It was a Vauxhall Cavalier and I was doing ~ 60mph when I removed my foot off the accelerator to let the car slow before braking and changing down in gear. I was nearing the end of a long drive down to Norfolk, it was a commute to work after a weekend away so I hadn't stopped on the way nor had I spared the horses. As a result I was feeling a little road weary and numb when the event happened but it was one of those occasions when the brain, once it kicked in, works so fast that time seems to stand still. It was also one of the few occasions when a voice in my head appeared and stopped me doing a couple of things that might have offed me before I hit the stone wall that lined the bend in the road that I was heading towards.

No foot on the accelerator and the car was still moving at pace with no drop in engine revs or the expected drop in engine noise, I hadn't a clue what was going on. It was as if that a demon had taken control of the car and was determined to kill me. I shook myself into action and thought to switch off the ignition to kill the engine. NO! Said the voice in my head. It explained that it would result in the steering lock engaging resulting in a further loss of control of the car and deny me a couple of other options that were steering dependent. What would anyone reading this do?

I survived what I opted to do and as I opened the door after stopping I was hit by an awful stench of a rubber/sulphur like smell. It was a blistering hot summer day with heat haze shimmering off the road surface and billowing from my front offside wheel was the steam-like source of the choking and repugnant smell. The smell was from the overheated brake pads that had just received some very judicious use.

So, could the source of your heat and smell from your rear wheel be a binding brake/brakes? Pads are a possibility but the most common I think is the shoes coming adrift from the backplate due to it rotting.

That sounds a horrible experience Steve!

Yes indeed when I went to dismantle the N/S/R the stiff wheel had got even stiffer, and freed up once the calliper was removed. I dismantled the calliper, cleaned it all up thoroughly and reassembled etc and now it works perfectly. So the stiff wheel, hot wheel and tyre and burning smell a bit like rubber were all due to a seizing calliper. The O/S/R had seized a couple of years ago and apparently they go close together so no surprise.

It still leaves me with the other wheel bearing-like and ABS symptoms, given the vibration and noise I am sure it is a bearing but TOAF doesn't specify which wheel. I will rig up a test lead as I have seen described in places and check the hard way.

Re the vibration, do the wheel and tyre look ok with no sign of a balance weight going awol?

Yes all fine, had new tyres recently but no change in the vibration at the time of fitting.

I have tried to make a test rig for the ABS but can't get it to work properly - using an old plug and socket, I joined pin 1 to pin 1, and then pin 2 to pin 2 but with an extra wire branching out to a chock block. On the next segment of chock lock another wire runs to earth. I am putting the multimeter into the chock block, + probe to the side with the wire from pin 2 and - probe to the side that goes to earth. Multimeter on the 20V range, ignition on.

It reads 10.66v - 10.69v, fluctuating randomly. Rolling the car forwards or backwards has no impact on the reading. I have tried this connected to both rear ABS connections. I was expecting to see step changes of 1.0v - 1.1v at intervals, but no, nothing.

I must be doing something wrong but can't work out what?

Sensors work in different ways. If I remember right the 75 ones use two current levels. Now that can also be measured as a voltage change. That would be done by looking for a voltage change between pin 1 and pin 2 on the sensor, rather than between either pin and ground. Does that make sense?

Did you make a test kit like this below.
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Hook it up to the car.
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Rear ABS.
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Wheel needs to be off the floor so you can turn it and take a reading, use the door stay as the earth, you are looking for 173/67 when you turn the wheel, these are the increments

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The fronts could be different
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good luck

Superb photos and instructions as always

Thank you chaps. I must admit I'm not very good with electrics, and can't get my head around how this measurement works (my brain isn't functioning perfectly atm anyway due to health issues!).

Steve Thank you for the photos, I am a bit confused though as the earlier photos have the negative probe going to the other sensor wire and the later ones have it going to earth. So for the later ones you effectively are tapping into one wire with the positive probe and then the negative probe goes to earth? Which is what I have done I think? Unless I simply am using the wrong wire for the positive probe but I thought tapping into pin 2 was correct as pin one was power, although the pins are reversed for opposite corners so shouldn't make any difference?

I am so confused now!

Duncan I think I understand that now, in which case you just connect the positive probe to the power feed and the negative probe to the signal? I did do that initially but in series not parallel and it just read 10V I think. But then the negative doesn't go to ground?

Bolin wrote:Thank you chaps. I must admit I'm not very good with electrics, and can't get my head around how this measurement works (my brain isn't functioning perfectly atm anyway due to health issues!).

Steve Thank you for the photos, I am a bit confused though as the earlier photos have the negative probe going to the other sensor wire and the later ones have it going to earth.

So for the later ones you effectively are tapping into one wire with the positive probe and then the negative probe goes to earth? Which is what I have done I think? Unless I simply am using the wrong wire for the positive probe but I thought tapping into pin 2 was correct as pin one was power, although the pins are reversed for opposite corners so shouldn't make any difference?

I am so confused now!

Yes the early photos are just how i keep them until I'm using the tool, so pay no attention to those, you need to earth to the car for the tool i made, i did give the owners club two sets so members could use them don't know what became of them?

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T4 (Testbook version 4.Computer Diagnostic System) would point out the trouble for you or at least it should. tool is good if you don't have access to T4

Thanks Steve, it looks like what I have made is basically the same circuit, maybe I need to tap the positive probe to the other pin? I'll try that temporarily before re-soldering (which will be difficult as I only have very little wire between the two plugs to tap into).

Yes, both wires from the sensors go to the ABS modulator / control unit. One is essentially a voltage regulated supply from the modulator so reading that relative to ground will be a constant voltage. 10v sounds right ish. The other pin returns the current to the modulator, but it controls the current depending on whether there is a magnet by the sensor or not. Essentially it swicthes in our out two different resistances, and that results in a change in voltage you can measure. You can measure it to ground, or to the other pin. The readings will be different, but you should be able to see the change in voltage as you turn the wheel. The two voltages in Steve's photos look right for a connected sensor in the two states.
Just to check, your adaptor. Pin1 to pin 1, pin 2 to pin 2, and a monitoring point (in Steve's photo, the choc block).