Identifying noises from my rear end!!

Post Mon Apr 14, 2014 1:05 pm

Having just got my 325i cab back on the road after being laid up for the winter, I was reminded yesterday of two distinct sounds coming from my back end that tell me something isn't right.

1. The first is almost certainly the diff - a second-hand LSD that I had fitted a couple of years back and I had filled with the correct slipper oil as well documented elsewhere on this site. The noise only really appears when the car is well warmed up and is a sort of growling/ low pitch whining noise that varies with the speed of the car. I'll change the oil and see if that improves things, but does anyone have any other advice??

2. The second one has always been there since I had the car, but is very distracting. It's hard to explain, but it almost sounds like the brakes are binding on nearside (the sound is definitely from that side of the car), but it doesn't vary much in pitch with the speed of the car, only in volume really and even then not my much - and it doesn't change at all when I apply the brakes, no matter how soft or hard I plant the pedal. My thoughts did turn the the fuel pump as that's located on that side as I remember - do these make a noise?

As always, all suggestions, comments, ideas etc will be gratefully received.

Post Fri Apr 18, 2014 8:41 am

It's not often that a technical query on here goes onto page 2 without a single response, so forgive me for bumping this to the top again.

Post Fri Apr 18, 2014 10:28 am

1) The diff. pinion bearing is shot.
2) Check if the handbrake mech. has come adrift.

Post Fri Apr 18, 2014 11:10 am

Jack up the rear a spin the wheels - could be noisy wheel bearings???

Post Sat Apr 19, 2014 7:09 pm

Brianmoooore wrote:1) The diff. pinion bearing is shot.
2) Check if the handbrake mech. has come adrift.

Cheers Brian - as dependable as ever to come up with suggestions/answers! Is the diff ponion something that can be repaired/replaced? Can you buy them as spares? I have a mechanic that would thing nothing of pulling it apart and replacing parts, but I guess it could be cheaper to just buy another one. Is this something that will eventually give up and jam up my wheels, or do I just need to turn up the radio and pretend it's not there??

I'll have a look at the handbrake mechanism tomorrow when I can get the back end up in the air.

Post Sat Apr 19, 2014 7:10 pm

miniblob wrote:Jack up the rear a spin the wheels - could be noisy wheel bearings???

I'll try this too - thanks miniblob.

I'll report back what I find.

Post Sun Apr 20, 2014 10:58 am

My money's on the wheel bearings (garage job) not cheap!

Post Sun Apr 20, 2014 12:58 pm

scallyally wrote:My money's on the wheel bearings (garage job) not cheap!

Not so. Easy enough to do by a home mechanic with a good choice of tools. My first one took half a day of fiddling and finding a technique, a lot quicker when I did the other side.

Post Sun Apr 20, 2014 1:15 pm

Noise from a wheel bearing various with hard cornering, either loading or unloading the wheel in question.

Post Sun Apr 20, 2014 5:24 pm

Brianmoooore wrote:Noise from a wheel bearing various with hard cornering, either loading or unloading the wheel in question.

Definitely don't have that - it's constant no matter whether I'm cornering or driving straight, accelerating hard or cruising steady.

Post Tue Apr 22, 2014 7:18 pm

Right, so having had the car running the wheels whilst up on a ramp, we've identified at least one of the noises. The first noise wasn't the diff - it's the nearside wheel bearing. The screwdriver stethoscope proved that. The hissing/scraping sound wasn't so evident though strangely - perhaps as no load was on the rear wheels? I've left it with the mechanic to do the bearing as it's certainly not a job I'd tackle, but asked them to look at the handbrake mechanism whilst they had it all apart in the hope the second noise is something to do with that.

All this is going to be costly, but I guess I should be thankful it's not my diff!

Post Tue Apr 22, 2014 7:31 pm

Check the condition of the brake back plate, especially where the handbrake shoe retaining pins fit. These can only be changed (without cutting and welding), if the rear hub is in pieces.

Post Tue Apr 22, 2014 8:43 pm

Will do Brian. Hopefully i'll be able to take a look at it tomorrow evening once they've got it all apart.

How long do you reckon it should take a mechanic to replace a rear wheel bearing?? They suggested 3 hours.