BMW Repair: rear end vibration, inclination angle, prop shaft

Question
QUESTION: I have a 2004 545 with a manual transmission. When I am travelling at around 70 mph, I get this slight vibration through the seats and shifter. above or below that speed, it is not present. I have done many things to eliminate this problem without success. I have had new rims and tire, balancing, new driveshaft, new rear rotors, new transmission mounts, readjusted the exhaust, suspension is tight. I was wondering if worn rear differential bushings would cause this. The bushing towards the rear of the differential looks worn but I'm not sure. What would be a good way to check for them being worn? thanks

ANSWER: Hello, I dont think a worn bush would cause a vibration, more of a deep thud or clunk. To check them prize them with a pry bar and look at the movement.You have spent a lot of money so far so lets try something different.

Have a good look at the prop-shaft, the front rubber coupling especially.Look at the 6 bolt holes and see if they look worn or have "moved".

Then have a good look at the rear cv joint, they wear out.Failing that there is a thing called "inclination angle", the centre support bearing mounting needs to be 2-4 mm past where it wants ti line up, so "pre load it " by 2-4 mm.

I realize you have replaced the "driveshaft" but was wondering if the front coupling, centre bearing and rear cv joint went back on.

Good luck

Tony

---------- FOLLOW-UP ----------

QUESTION: Thank you for you fast response. In regard to preloading the center bearing. Would that cause a vibration? I didn't prepossessing it when I changed out the driveshaft. Just tightened it where it lined up. The rear differential bushing appears to have a split on the bottom and seems to be more pliable/rubbery than normal. Any thoughts on this?

Answer
The center bearing preload is critical for vibrations, a worn rear bush (collapsed) would change the "inclination angle" This is the angle at which the driveshaft meets the diff.

these are bastards to find, best of luck, try the centre bearing preload first, its easier.


Tony