Grinding Noise from rear of car after rear suspension work

[eelley]

Hi folks,

Took my car in for service a few weeks ago and had the following replaced: rear stabilzer bar links and bushings, rear trailing arm links, trailing arm bushings and rear carrier mounts. The car had excessive vibe from the rear especially at 60-70 mph. This was the first time in a looong while that I did not perform all the work myself. It is starting to get cold here in New England and I did not have the time to do the work myself.

They replaced everythng above plus they replaced the passenger side rear tire, which had chunks of rubber taken off it along the inside edge.

After the repair, I drove the car out of the lot and there was a HUGE rubbing sound coming from the rear end of the car when accelerating from a stop. I never heard that sound prior to taking in for suspension work. I drove the car back and no sound. In fact I drove the car around for the better part of the week and nothing. I figured that was strange. A few days later I jacked the car, crawled under it but did not find anything (that I could see) out of wack with the exception of oil spattering near the input flange of the rear diff.

Then after driving long distances (over twenty miles) the sound is back but not as loud -- in fact you really have to drive pretty agressivly to get it to do it. It does not sound like wheel bearings because it does not disappear when steering and neither does it sound like the thub, thub, thub of a center drive shaft support bearing. To me it sounds like a grun, grun, grun -- like the tire rubbing on the top of the wheel well - which it is not).

The repair shop that did the work did the repair for a price that was REALLY cheap (like $600) so I felt a strange taking it back. So I drove it to my local BMW $tealer and thet said that I need: A differential (leaking), center support bearing (which they said was not bad but on its way out), engine mounts (dangerously deformed), and a driveshaft.

Does it sound like they really can not determine what it is and are (with exception of the engine mounts)repalcing everything? The price of parts which totals about 2.8k is about all that I could take.


What do you all think?


Stuff I have already replaced myself:

Radiator (rupture)
Water Pump (leaking)
Intake Reseal -- Valley Pan (Leaking - Poor Idle)
Fuel Injectors and Coils (all of them - misfiring - some coil casings cracked)
Valve Cover Gaskets (leaking)
Microfilter (Clogged)
Auxillary Cooling Fan (not running)
Blower Motor (died)
Right Window Motor (died)
O2 Sensors (Check Engine Light)
ICV (Cleaned)
Crank Position Sensor (car would not start)
Fuel Pump (died on a highway)

I really love this car but I am wondering what will go next....


Thanks for your help,

Eric

[attack eagle]

swap the diff yourself.

6 nuts on the flange, the CV outputs, and then only 3 bolts hold the diff in the car.

A whining noise could indicate it is on its way out...


could also indicate that it simply is low on fluid so try changing or topping that off first.

[eelley]

There is a leak around the input flange of the diff. So I am assuming it is low.

Is there a special type of oil I should purchase?

I have never changed it and I have had the car for about 100k. I never thought I had to, and now I am paying the price. :(

Thanks,
Eric

[ThoreauHD]

I would do maintenance first, before you start replacing parts like it was a legomobile. The only thing on that list that is not iffy are the engine mounts and something you didn't mention yet- the flex disk. You will get a thump either from the flex disk or the engine mounts not being there anymore. Both have the same effect at acceleration. So now..

Your mounts are with near absolute certainty exploded. Our V8 engine crushes them into paste. I would have the indy mechanic do that, not the dealership- and not you. Unless you like pain.

As far as the rubbing sound at acceleration, I would also look at the rubber grommet holding your transmission together. The flex disk/guibo. That also fails quite spectacularly at your mileage. Mine looked like a pack of rabid gerbils molested it for a week and forgot to leave their number. But before you do all that high labor stuff, do maintenance. Btw, the engine mounts and flex disk will cost you about 10 hours labor at the shop. And it will probably take that long depending on how skilled/equipped they are.

If you haven't moved to Amsoil 5w-40 or any other type of synthetic properly weighted oil, do it. Do the oil and filter. That part is easy. And I'm not getting into an oil debate though. Amsoil and Redline and Royal Purple and maybe Motul are all good. Mobil-1 used to be good but is now dogshit. End of the debate that I wasn't going to have.

And yep, there is a special oil for the differential/transmission. You should buy the items below.

4 Quarts of Red Line D4 Synthetic Transmission Fluid

2 Quarts of Red Line Synthetic Differential Fluid - 75W90

1 Automatic transmission filter kit(Part # 24341513KIT at bavauto.com)

1 Differential input seal & 1 output seal

You will need an oil transfer pump for 20 bucks if you are doing it yourself.

And considering this is the first time you've done this, I would get 2X what I said because you'll probably need to do it again in another 3K miles. You are only optimistically changing about 2/3's of the fluid when you do this.

And what will you get after going through all this? A new car. Your car will glide, and will shift without a thump or sound.

So, to sum up. All fluids and filters first. Do engine mounts and flex disk if symptoms persist. The end.

PS- If none of the above work. Here are my apologies in the form of a **** sandwich.

http://i4.photobucket.com/albums/y106/toasty0z/****-sandwich.jpg

[Ross]

Initial sound could have been a deformed brake backing plate rubbing.
Why would you feel awkward about returning to a shop that had done the original work?
If the leak on the diff isn't bad just replenish the fluid as needed. Why perform an expensive repair when the only consequence of the failure so far is a little oil splashed under the car?
Rebuilt driveshafts are available now for a couple hundred bucks, the center bearing and flex disc will add a bit less than a hundred and should be done unless already replaced. The labor to change the driveshaft neccesarily includes the removal and replacement of those two parts so it's a no brainer to do 'em at the same time.