What’s wrong with my M3?

[_Tim_]

My M3 is making worryingly expensive sounding noises at the rear. It’s a cyclical crunch/grind type of noise not dissimilar to the sound you would hear if a tyre was rubbing on the wheel arch (it’s not that!).

It’s only really noticeable while turning and at lowish manoeuvring speeds, and seems more prevalent when the car is hot after being driven for a while. I think it’s coming more from the offside. It’s been doing it for quite a long time, but since I had the car polybushed last week it’s much more obvious. I’m looking to sell it soon so I need to get whatever it is fixed.

Could it be something as simple as a wheel bearing? Or more likely to be a ££££££ diff problem? As a precaution I checked the oil level in the diff but it only took a few CCs of fresh oil. The diff oil was changed (with oil supplied by a BMW dealer) less than 10k kms ago.

Thanks,
Tim.

[petro]

sounds like wheel bearing

[Mmark]

Drive the car around a roundabout. You'll be turning right.
Is the sound louder?
If yes...left side wheel bearing.
If no... find somewhere to make a longish left hand turn.
is the sound louder?
If yes...Right side wheel bearing.
If no...and sounds the same as the roundabout.... problem may be in the diff , but also check out the center driveshaft support bearing.

m

[m3ubbs]

My front left wheel bearing went out a while back--my car sounded like prop engine at about 40mph. Did the roundabout test mmark is talking about and it was an easy fix from there. Rear bearings are cheaper. However, it shouldn't matter whether or not your car is hot or not, the wheel bearings should make the same sound.

[LINUS]

I'd guess w.b. too - really not much else there - how many miles/km's since last bearing change? If you make steering locked circles in a parking lot which outer side wheel sounds worse (if either) ?

HTH-

---Ben

[Mmark]

Tim .
did this noise start after the diff fluid was changed?

If so, ask the dealer what weight of oil they used.

E36 and E46 M3s are sensitive to the weight of the diff fluid used.
These cars have noisy diffs if the incorrect weight of fluid is used.
As soon as the fluid is replaced with the correct weight fluid, the noise disappears.

I believe they use a similar design innards in the E30 diff.

Make sure they use the correct weight of oil. 75-90.


m

[Jake]

Amoung probably more likely culprits (wheel bearing), have a quick look at your brake backing plates; if nothing else to at least eliminate something cheap. The backing plate has a ring spot welded to it that closes the gap slightly between disc and the backing plate. Sometimes it begins to rust between the ring and the backing plate which causes the ring to raise up and contact the disc. You hear it rub slightly in slow turns. If this is the problem you'll see it quite easily if you pull the disc off and inspect the backing plate. Contact will be obvious by shiney spots on the backing plate ring. If this is the case all you need to do is give it some clearance by bending it slightly. Keep in mind bending it may pull the other side into contacting the disc. The long term fix is of course to replace the backing plate (still cheaper than a wheel bearing).

Although it sounds like you've got a wheel bearing going bad, this is something easy to check. Could save ya some cashola.

Hope this helps,
Jake

[one_owner]

***It’s only really noticeable while turning and at lowish manoeuvring speeds, and seems more prevalent when the car is hot after being driven for a while. The diff oil was changed (with oil supplied by a BMW dealer) less than 10k kms ago***

buy some limited slip treatment and put it in the diff. it usually comes in a toothpaste style tube. pat yourself on the back for a $10 fix.

hth,
greg
garber's

[JS154]

Sounds like a CV joint going bad. easiest thing to do would be to chuck a used axle half-shaft in there, any E30 one will do, they are all the same.

A wheel bearing will make a distinct "wooga-wooga-wooga" sound. A bad cv will sound much more serious, at first it sounds like a click-click-click but as it deteriorates it will ultimately sound like 3 aluminum baseball bats being rattled around in a meatl trash can.

[_Tim_]

Well thanks for your input guys. I just drained the diff oil and replaced it with Castrol SAF-XJ.



Problem solved! Gotta love those cheap fixes...

[petro]

good to hear. where did you get the Castrol SAF-XJ from?

[Lumanikus]

Originally posted by one_owner
***It’s only really noticeable while turning and at lowish manoeuvring speeds, and seems more prevalent when the car is hot after being driven for a while. The diff oil was changed (with oil supplied by a BMW dealer) less than 10k kms ago***

buy some limited slip treatment and put it in the diff. it usually comes in a toothpaste style tube. pat yourself on the back for a $10 fix.

hth,
greg
garber's

The slow speed is what gave it away. I made the mistake of ordering NS redline fluid and then had to add the treatment later. Im changing mine out again because im paranoid and it could be more quite.

[_Tim_]

Originally posted by petro
good to hear. where did you get the Castrol SAF-XJ from?

I got it from Opie Oils (http://www.opieoils.co.uk/)