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For the last number of months, I'd had severe steering wheel shakes under heavy braking, but only when the car had been moving for a longish time (- probably more than 40 minutes). The ABS ECU had logged faults something like 'front left speed sensor intermittent fault'. I'd removed the sensor a couple of times (wheels still on ths car) and there was quite often, a bit of debris stuck to the bottom of the sensor. I cleaned this off, put it back and went on my way, but the problem kept coming back.

A few days ago, I removed the front wheels so I could remove the two ABS sensors again. This time I was able to also look through the now empty sensor hole, at the reluctor ring below (on the hub). When I rotated the hub, I could see debris clogging up some areas of the reluctor ring - see below:

[attachment=2:fa28nwxu]paul.adshead.ABS.ring.clogged.jpg[/attachment:fa28nwxu]

After 20 minutes with a screwdriver, some turps, an old toothbrush and the compressor/air-gun, this is what they looked like (around the full rotation):

[attachment=1:fa28nwxu]paul.adshead.ABS.ring.clear.jpg[/attachment:fa28nwxu]


What I guess had been happening here, is that at certain portions through the axle rotation, the ABS sensor could not distinguish between the clogged 'gaps' and the 'peaks' on the ring and thus the ABS computer would not have been seeing any 'state changes'. As the ABS computer is measuring the time between impulses from the peaks on the ring, to work out axle speed, then at cetain parts of the rotation, the ABS computer would see one long pulse, instead of the regular stream of short pulses. If you happen to be braking when the ABS computer sees this one long pulse, then it interprets this as a low-speed/locked wheel and thus drops hydraulic pressure to that wheel. As the wheel is NOT actually locked/skidding, but has good traction and as the other brake on the axle is hard applied, then one wheel pulls rearwards a LOT harder than the other. Thus causing the steering to pull to one side. As the ABS system pulses the faulty side back on/off again, then you see this in the steering wheel as VIOLENT shakes, side to side. The only way to remove the steering shakes is to totally come off the brakes and gently apply them again - not good when you barrelling into a corner.....

The crud that I scraped out of the teeth on the reluctor ring, was a gloopy, gummy rubbish. It was apparrent that whoever had been in there beforehand, thought it would be a great way to hold the sensor firmly into the hub-carrier, by covering the sensor in this rubbish. :-(

RAVE says the following on the subject:
11. Lubricate new sensor bush with silicone grease.
See LUBRICANTS, FLUIDS AND CAPACITIES, Information.
12. Fit sensor bush.
13. Lubricate sensor with silicone grease.
14. Push sensor fully into bush until it contacts
reluctor ring. Correct sensor position will be
gained when vehicle is driven.

I only hope that the 'official' "silicone grease" isn't this crap I scraped out off the ring. If so, there will probably be A LOT of vehicles around with this same issue, where too much grease has been applied. I didn't use silicone grease, but instead used some of my trusty 'coppercote'. As coppercote is a very 'soft' mixture, any that should get onto the teeth on the ring would be thrown off again - not be stuck there forever and cause on-going problems.

Whilst I was in there, I thought I'd take a pic of the "sensor bush" too. Quite why RAVE insists a new bush needs to be used every time the sensor is removed, makes no sense at all to me - there is plenty of adjustment in the bendable teeth on the bush.
 

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Thanks for a great post and the perfect detail of the parts. I assume the issue is resolved. :D
 

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I was having an issue with water getting into the axle through that ABS hole. The silicone grease is important to pack in there to prevent that from happening. I use the clear dielectric grease that looks like vaseline.
 

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Discussion Starter #5
diff said:
I assume the issue is resolved. :D
No problems experienced since, but haven't been on any really long drives since either. However, from the debris I saw and thinking about it afterwards, it does all fit that this was the cause. Regarding the issue only happening after more than ~40 mins driving, then this is probably the amount of time for the gummy residue to get warm. Once it's warm, then it would start to stick to the sensor more, causing the sensor to have even more troubles differentiating the peaks from the gaps.
 

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Discussion Starter #6
Jsmooth65 said:
I was having an issue with water getting into the axle through that ABS hole. The silicone grease is important to pack in there to prevent that from happening. I use the clear dielectric grease that looks like vaseline.
I'm guessing you are talking about the rear axle? My issue was the front axle ("steering wheel shake").

On the front axle, the grease is most definitely NOT part of any water/oil seal on the axle. If you look at the pic below, you can see the ABS sensor mounting hole (- circled in blue), is well away from the end of the axle/oil-seal (- the centre of the pic).
[attachment=1:1zgntkmk]paul.adshead.front.ABS.sensor.jpg[/attachment:1zgntkmk]
Regarding the rear axle, and waterproofing then I don't have any first hand experience of this. However, I am having big problems believing that a seal on the ABS sensor, is keeping water out the the diff oil in the axle. If that was the case, then it would mean that the ABS reluctor rings on the rear axle, would be running in diff oil and throwing the fluid up all over the sensor - which just wouldn't work. After looking through RAVE, it looks to me, that the rear ABS sensors, are supposed to have a small sealing ring (- the middle item numbered 4 below), between the sensor and the ABS bush (see below), though I'm not sure what this is supposed to be sealing. The oil seal that keeps diff oil in the axle casing and other stuff out, fits between the end of the axle casing and the hub (- the item numbered "7" below).
[attachment=0:1zgntkmk]paul.adshead.rear.hub.jpg[/attachment:1zgntkmk]

Wherabouts in which axle was the water getting into? What had you been doing before it happened - water crossings/jet wash/etc?
 

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I meant it was getting into the hub/bearing housing through the ABS sensor hole, which caused some substantial rusting and foaming where the ABS teeth are. Some of that water eventually found its way through the axle seal and into the diff case.

And yeah, I found this issue on the rear axle, not the front. The little rubber cap that fits on top of the ABS bushing was intact as well, which is why I felt that the lack of grease in the bushing was the culprit. The front instructions say to grease up the bushing, too, so I figure it may help, right?

Oh and by the way, that brass bushing is like $40USD from the stealership, and the rubber cap is like $20USD. Insane.
 

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An update, 2 months later..

So this issue (steering wheel shakes) came back. I've since changed the front brake rotors and I believe i have now finally solved this issue. Cleaning the ABS reluctor rings, definitely made a difference/improvement, but I think my rotors were also part of the problem.

After reading RAVE, new front rotors are 25mm wide and 'worn' (= throw away rotors) are 22mm wide. I put my digital vernier on the rotors I took off, and it said they were 24.8mm (- so they should still have plenty of life left), but were obviously slightly buckled/warped. I priced up resurfacing the rotors, but replacement with new, was only twice the resurfacing cost. I went with new rotors.

I glad this is now resolved. It was not a good feeling, wondering if this corner, the steering would shake and you would have to let off the brakes...

After I fited the new rotors, I went for a drive. I touched the discs after the drive and I singed the ends of my fingers! :shock: Touching the old rotors after a similar drive didn't do that. I can only assume that the new rotors are thus better are removing heat (in this case into my finger), and thus will be better during heavy/sustained braking.
 

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paul.adshead said:
An update, 2 months later..

So this issue (steering wheel shakes) came back. I've since changed the front brake rotors and I believe i have now finally solved this issue. Cleaning the ABS reluctor rings, definitely made a difference/improvement, but I think my rotors were also part of the problem.

After reading RAVE, new front rotors are 25mm wide and 'worn' (= throw away rotors) are 22mm wide. I put my digital vernier on the rotors I took off, and it said they were 24.8mm (- so they should still have plenty of life left), but were obviously slightly buckled/warped. I priced up resurfacing the rotors, but replacement with new, was only twice the resurfacing cost. I went with new rotors.

I glad this is now resolved. It was not a good feeling, wondering if this corner, the steering would shake and you would have to let off the brakes...

After I fited the new rotors, I went for a drive. I touched the discs after the drive and I singed the ends of my fingers! :shock: Touching the old rotors after a similar drive didn't do that. I can only assume that the new rotors are thus better are removing heat (in this case into my finger), and thus will be better during heavy/sustained braking.
Paul, did you replace the caliper guides too?

I had the shakes under braking and went down the new rotor road, when I went to change them I found one of the right hand caliper guide was stuck fast in the carrier, the whole lot had to be replaced in the end.
Due to the stuck guide the brake pads on that wheel were only giving half contact compared to the other wheel, hence the shakes :!:

SID.
 

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Discussion Starter #12
SID said:
Paul, did you replace the caliper guides too?

I had the shakes under braking and went down the new rotor road, when I went to change them I found one of the right hand caliper guide was stuck fast in the carrier, the whole lot had to be replaced in the end.
Due to the stuck guide the brake pads on that wheel were only giving half contact compared to the other wheel, hence the shakes :!:

SID.
Hi Sid,
I investigated the guide pins, all were free to move in the caliper, but I removed them all anyway, cleaned them up and re-greased them.

Re-greasing was a bit tricky. If you put too much grease in, you end up not being able to push the pin back in the caliper - the trapped air/air-pressure, just pushes the pin straight back out again.... As each pin has three 'flats' running the full length of the pin (presumably to allow the grease to move around), I found the best way, was to: wipe the pin clean; put the grease on just one side of the pin; insert the pins as far as possible; then twist the pin around. Thus the grease is spread around inside the tube.

It's good to have it working properly once again.
 
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