e28 Rear suspension help needed - vibration/rumble/thumping noise

["Omar Akbar Khan" <dxramo@xxxxxxxxxxx>]

The car in question is a 1988 535i. When I bought the car, it was 
experiencing the typical symptoms caused by rear-support bushing(s) wear 
(loose rear-end, "4-wheel-steering") and also a lot of vibration from the 
rear-end under acceleration.
I took it to a pretty reputable shop in town specializing in BMWs, and they 
replaced the two rear-support/sub-frame bushings (the ones right in front of 
the rear wheels), and also put in new front end bushings (shaved 750 
bushings). Total bill around $650.
I took the car out of the shop, and the front end was really tight, but 
there were still some vibration from the rear-end (though it was much better 
than before - the looseness in the rear was gone). In a day or two that 
vibration turned to a "thumping" noise coming from the drive-shaft tunnel. 
Took it in again, and the center-support bearing for the drive shaft was 
replaced. Total bill approx $280.
Took the car out of the shop.. everything was perfect I thought. Got on the 
highway, and while accelerating on the on-ramp,  the thumping noise started 
coming again.
Took it back again - I was told that it's the center-support bearing again 
(previously the bearing itself was not bad, but the housing in which it sit 
had been broken loose - from the vibrations presumably). They said that 
probably the vibration or something was causing that bearing housing to 
fail/break, and since the rear-bushings had been replaced, the other thing 
to do was to replace the rear-end bushing - which I was told is the third 
point of failure in the rear bushings (first two being the other 
rear-support bushings that had previously been replaced - though I still 
wonder why this third bushing wasn't replaced the first time when they 
replaced the other two rear-support bushings). The vibration/thumping had 
gotten so bad at this point that even under light acceleration, the 
"thumping" of the drive-shaft against the drive-shaft tunnel was very loud.
Car went in the shop, the center-support was replaced under warranty, and 
rear-end bushing was replaced. Car rides much better and concise now and the 
rear end was raised up about an inch, and seems to "sit" better, and handle 
MUCH better - I presume the way it should.
*BUT* the "vibration/rumble" is still present in the rear-end under 
acceleration. The shop said they don't know what it is, dont' know how to 
fix it and that they have tried everything they knew. Under even slightly 
heavy acceleration (half throttle), the vibration starts, and turns to the 
"thumping" noise that is supposed to signal center-support bearing failure. 
I noticed this morning that the thumping is more prone to start when taking 
a right hand turn and accelerating. Under light acceleration (quarter 
throttle), the vibration is light and just present for a second or two - but 
as it did last time, I'm sure it's going to get worse and the center support 
bearing is going to need replacement again (though when I say "light 
vibration", I'm being very relative.. the light vibration is heavy enough 
that when it happens, the steering wheel vibrates/moves up and down about 
half-an-inch).
I was told to "just drive the car easy" and live with that vibration, and 
that way the center support bearing will not fail again. They said they have 
seen this with a few other 5-series and they don't know what it is.
Bill this time for rear-end bushing and a cracked engine mount  - $210.
Total expenditure so far has been about $1140 but the rear-end problem is 
still there.. needless to say, I'm very frustrated.
If I wanted a car that I wanted to drive easy, I'd go and buy a Hyundai or 
something (no offense to hyundais or their owners - just trying to make a 
point).
I know the shop is very reputable, and they are very clear about what is 
wrong and what is not etc etc.. but I can't seem to just rest with the idea 
that this cannot be fixed and that there is no solution.
if anyone could give me ideas/thoughts/previous experiences with this type 
fo problem, I'd really appreciate it. I seem to remember someone recently 
mentioning that the rear-end needed to be pre-loaded before installing the 
rear-support bushings? Does that apply in my case?

Thanks for any help in advance.
Omar. (I apologize for the long e-mail.. but wanted to make sure I explained 
the sequence in which things were done in case that is a clue)





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