propshaft problems

ok ..had the car in the garage today,lot of vibrations going under the car....suspect propshaft center bearing...exsposed the propshaft after a good days work droping the exshaust..found the bearing and the propshaft to be ok,much to my disapointment.in saying that i can move the shaft up and down in the rubber mouting. sould i be able to do that,,i dont know how tuf that rubber sould be....... the car is a 1990 bmw 750i...... checked the sevice history and the prop and bearing was replaced in 2000 at 104000 miles ,now done 130000 miles .also the gear box mountings in good condition .........RALPHIE

on the drive shaft, and at the same time the engine mounts as well as the transmission mounts.
I just changed the engine mounts on a 750, the new mounts are 2 mm higher than the old ones, and is too much. Even if you change the center bearing, the drive shaft is still not in the right straight position like it should be, if you do not change the transmission mounts and the engine monts at the same time.
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Center support can also wear faster than normal due to bad U joints on the drive shaft. U joint bearings can get tight due to lack of lube after time on one axis, disturbing the natural balance. Overall shaft may feel "good" since its not sloppy. It's harder to detect binding unless it's removed. Ken Ken

92-BMW 735iL
74-Widebody Porsche 911S
03-Explorer
81-VW Caddy
<img src="http://i36.photobucket.com/albums/e31/kwandrey/911-2.gif">

I had a guy in not to long ago who had tried a new shaft to get rid of a shake. After many other tecs looked in the shake I found a bent wheel. I can see how with these cars you can suspect a drive shaft from the way it feels.

...both the front U-joint and the back CV joint have to be loose from the trans and diff respectively before you can tell what's really wrong.