Need help diagnosing a rear end noise

[mightydave]

I've had my recently purchase 850 CSi on jack stands this week as I refinished the wheels. Yesterday, I mounted the wheels and drove it a bit - roughly 5-10 miles.

On the way home, I noticed a ticking coming from the rear end - and from inside the car it sounded like it was located near one of the rear wheels. At slow speeds, it sounds pretty loud and it sounds metallic.

I checked again today, moving at slow speeds, and it's still there.

* It only makes noise when in gear - never just rolling
* It's consistent, and follows the speed of the car - like a rotational sound - makes the sound once per rotation, etc.
* Can happen in a forward or reverse gear - but only when fully engaged
* Does not make the sound when the rear is lifted - only when on load. If I apply the emergency brake part of the way and put it in gear, it does make the sound.

It's a clang. Definitely doesn't sound "good".

It sounds like it's centered near or around the rear diff.

Anyone care to educate me on what it could be?

[Dr. T]

Check Driveshaft and Output shaft boots

[Timm]

That is sure to be the CV joint where the propshaft meets the diff - the grease dries out and you will start to get clanging noises - and then vibration as you accelerate. Fortunately it is available as a separate part and is reasonably easy to change:

http://www.meeknet.co.uk/e38/e38_remove_propshaft.pdf

I've had a couple of them fail and it is best to do them sooner that later!

[mightydave]

Hey guys - thank you. Timm - is it part # 26-11-1-229-099 or am I looking in the wrong spot?

[Timm]

Yes, that's the one:

http://www.realoem.com/bmw/enUS/show...98#26111229099

[mightydave]

Quick update and a follow-up question.

Got started on replacing the CV joint and the guibo last night. Exhaust came off easily. Removing the drive shaft was also pretty easy - with a little help from PB blast to loosen things up a bit.

Before removing the drive shaft, moving the wheels even a little bit replicated the sound I was hearing (a pinging) right at the CV joint - so it was clear that was the issue.

Got the old CV joint off and got the guibo off. No problems there.

When putting the CV joint back on the prop shaft, it did not want to go. I assumed it would just slide on - even though getting it off required help from a mallet. Ultimately it went on and we started packing it with grease. That's where my question comes:

After the grease packing, should the CV joint show lots of mobility (smoothness) when rotating? I assumed it would because of the ball bearings, but it definitely doesn't. I'm wondering if we should pull it off and grease it with it off so that more grease fills the boot.

Timm - thanks for sharing that link. That was hugely helpful last night.