ABS wheel speed sensors

[nothappyjan]

Hey Folks,

The wife has a VR Acclaim (1994) with a very noise drivers side front wheel bearing for the last 8 months. Being on annual leave and having nothing better to do, I'm trying to fix it. After inspection, I found the whole hub needs to be replaced rather than just the bearing - which is annoying, but so be it. After the ring around, I found that even aftermarket outlets have outrageous prices for new ones, probably cause there are only genuine ones available.

Next, I rang around some wreckers and found one in Melbourne with a second hand ABS hub for around $100. After putting it in with my VERY enthusiastic 10 year old son, we took it for a test drive. Reversing out of the driveway appeared promising. But upon applying the brakes driving forward we found a pulsating noise for the next few brake pumps followed by the ABS OFF light appearing on the dash. After the light came on, the brake pulsations were gone. I assumed the ABS had switched off and the brakes were now operating as non ABS brakes. We confirmed this by appying enough brake force to skid the front wheels. After stopping the car and restarting, the ABS light was off but the same thing happened as before.

Luckily, being an electronics engineer, I have a digital oscilloscope with which I can measure and see voltage waveforms. I measured the pulse output of the old hub rotor. It's probably a reluctor which is a magnet and coil. Every time a magnet runs past the coil, a voltage is produced. The signal was a well shaped sine wave.

We took off the second hand rotor and also measured it's waveform. The speed at which I turned the rotors was approximately the same but I found that the frequencies were VERY different (around twice). Just to make sure the signal was actually getting through, I tested the rotor output at the connection under the bonnet, just near the ABS actuator unit (after re-installing the second hand unit). It was fine. A quick test drive confirmed the problem still exists.

Finally, here are my questions:
- Are there ABS hub rotors with varying pulses per revolution?
- Is the second hand rotor I purchased for another vehicle?
- Am I supposed to change both front hub rotors using a fequency matched pair?
- Is there an adjustment in the control unit to match the frequencies?
- Is it possible to disassemble the old hub rotor and swap the reluctor? I've managed to remove the large bolt from the old hub using a modified socket and 1m long steel tube.

I now have an old hub rotor with a crook bearing/ good reluctor and a second hand rotor with good bearing /incompatible reluctor.

Therefore please help. The Missus is getting edgie (for want of better wording) and my annual leave is dwindling quickly.

nothappyjan.

 

[mixin]

There are 3 types of front hub.

Non ABS (no tone wheel)
ABS with live axle
ABS with IRS.

The 2 ABS hubs have a different pulse count per revolution - as you suspected.

The hubs themselves were colour coded when new, but it may be hard to see on a 2nd hand one.

The non-ABS one is easy - no tone wheel & it's plain steel.
ABS & IRS ones had grey paint on them from the factory.
I can't remember the ABS/live rear colour!

Anyway, the reason they are like this is because the rear tone wheels in a live axle are on the axle shafts, and sensors are fitted in the diff tubes.
These tone wheels are limited in size to what can fit in the diff tube, and can only get a few pulses per revolution in (I think it's 12 or 15 from memory).

The IRS rear tone wheels are mounted on the sides of the diff - and have like 40 odd teeth - or more!

The 2 types of front ABS hubs have different pulse counts that relate to the different rear counts - obviously the one off an ABS/IRS car will have a lot more pulses per revolution than a live rear.

This was done that way so the ABS computer remains the same for both types of rear end - as the pulse counts are still in relation to each other.

There's not much you can do bar swapping the hub for another one of the correct type

 

[nothappyjan]

ABS front hubs

Thanks for the fast reply Mixin.

A couple of things though.

- The original sensor wheel is black and the second hand one is grey. This is the plastic doughnut shaped thingy with electrical connector on it that plugs in when you bolt it onto the front strut assembly. The rest of the hub is metal.
- Can the sensor wheels be changed? I have removed the main bolt from the original hub but don't want to continue for risk of damaging the sensor wheel. I'll need to put this back onto the car until I can find another.
- Im a little confused - ok, a lot confused - about the types you mentioned. You can rule out the non ABS type but how do I explain to a parts wrecker what type I need. Where is the colour coding you mention?

Thanks,

nothappyjan

 

[nothappyjan]

ABS wheel sensor types

Mixin,

I think I worked it out now. My VR does NOT have IRS and the type I purchased has a grey rear which is for IRS models.

I need another black one as per the original, right? And when getting another, I need to tell them my VR does not have IRS, right?

 

[Jason]

Yeah i think you got it there. Thats interesting about irs/non.
Funny though, youre sure you aint got IRS? :yeah: ...not meaning to insult you...i though IRS came standard on the acclaims though.

One of my mates had to replace his non-abs bearing, that cost about $300 apeice , and he reckons new ABS ones are between 500 and $800, so if you can find a goodd one for $100 thats pretty good.

 

[nothappyjan]

IRS/ non IRS

Jase,

Your point is very valid and Im not insulted in the least. In fact, I just got out the torch and had a look under the VR. The diff is a standard type, ie. completely sealed and straight like any old diff from cars dating back decades. I assume the IRS diffs are the ones with swinging drive shafts connected to the diff by CV joints like on my VX. The two back wheels therefore swing independently and I assume this is what is meant by Independent Rear Suspension.

It's definitely a VR Acclaim as shown by the badge, rego sticker, manuals etc. My Haynes workshop manual shows my model is one of the first VR Acclaims made for a few months only.

I bought the hub from Holdent in Melbourne on Tuesday. I'll try to get another tomorrow. If I cant swap it or get a refund, I'd be interested in selling it to a good home for the same price ($110). Its also been tried and tested. The sensor works and bearing is ok.

Cheers

nothappyjan

 

[Jason]

Yep, thats it exactly - with IRS the diff is bolted to the Chassis, and you got the two drive shafts coming of, they can swing up and down.
Maybe its just the vs acclaim thats IRS standrd, anyway, hope you get it sorted. should be fine with the right hub if you can get it.

 

[mixin]

The paint was normally applied to the outside of the hub - in the centre spigot area where it was easily checked on the assembly line.

Now you mention it, the connectors for the 2 types are different colours from memory too!

I have no idea about swapping the guts over as I have never tried.

Your acclaim is correct with the live axle if it is one of the first couple on months production - it didn't become standard IRS in the acclaim straight away, and you are spot on with your undercar observations.

I would definately try to swap it - technically they have sold you an incorrect part, and maybe they could do with a lesson in parts identification?

 

[nothappyjan]

Thanks all.

I shall call Holdent tomorrow (today??). They wont have another as they said this was the only VR ABS one. I'll try Prowreck as I need to go to Dandenong anyway. Holdent never mentioned the IRS/ non-IRS issue and neither did I. I assumed there was only one type. Can't really blame Holdent as I didn't give them enough info either.

Seems a shame I can't pull apart the other hub to swap the sensors. When I do get another hub (the correct one), I'll have another go pulling apart the old hub, now that I have taken off the main bolt. Perhaps I can get at the bearings as well. Hey... there's something in that for everyone.

Tune in soon for the concluding episode ....

Alittlebithappier

 

[nothappyjan]

VR ABS hubs- the concluding episode

Hi All,

Good news! I went back to Holdent who tried to find me a ABS non IRS hub but without success. They then proceeded to give me back my money without question. I'm a salesman and with my experience with some shops in mind, was still impressed with the service regardless of being unsuccessful with the part I needed. I would still thoroughly recommend them as they were still very friendly about it.

Moving on now, I went to Kumbak whom I called earlier this morning and who told me they would definitely have the part somewhere. It's only 10 minutes from Holdent so the drive was quick. Very busy place (which I like cause it shows they are popular) and after a short wait I had the part in my hand costing - wait for it - $66 inc. GST.

Incidentally, the hubs have the models and some other SKF bearing stuff engraved on the side of the disk. If I was bothered to clean the part a little with a wire brush, I probably would have found it yesterday. The hubs for IRS cars have RH48 and for non IRS RH32. The number denotes the number of pulses per rev as Mixin pointed out. Therefore the identification of this part cannot be mistaken.

Low and behold, I was on my way back with the correct part for less money. I installed it, tested it (the ABS OFF light stays off) and suddenly the sun was shining, the birds were singing and the Missus gave me a microsmile reward.

With the money I saved we are going to the cricket on Monday for the Tsunami appeal match. It's all good.

Until next time.

Quitehappynow