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Matt
Matt, Mechanical Engineer
Category: BMW
Satisfied Customers: 20593
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a 1995 E34 525TD touring with auto box. Within the

Customer Question

I have a 1995 E34 525TD touring with auto box. Within the last 200 miles or so I have noticed a strange noise when overrunning at high speed. The conditions for the noise to occur are 1) vehicle warm, 2) speed at 80 mph or more, 3) torque converter lock engaged (direct drive), 4) lift off throttle. A rapid rhythmic sound can be heard while the revs fall from 2000 to 1700 or so. On occasion the sound is louder and on occasion it is quieter. I was travelling home on the M6 Toll road last night and the sound was very pronounced, then there was a "thud" and a rattle as though something had fallen of underneath the car and the sound immediately faded. I have looked under the car as best I can but nothing seems to be adrift.
Submitted: 10 days ago.
Category: BMW
Expert:  Matt replied 9 days ago.

Hello

From your description I'd suspect that the propshaft either has a worn joint or the centre bearing is worn or its out of balance

you can easily check for for any slack in the propshaft joints by twisting either half by hand and feeling for any play as there should be virtually none

the centre bearing is quite loosely mounted so this can be moved normally but if you can run the car in gear with the wheels off the ground and then feel the centre bearing housing for vibration if there's any then consider replacing the unit

and then look along the propshaft for any signs of a missing balance weight as these take the form of little 3/4" squares that are welded onto the shaft - as they are only tacked on they can sometimes come loose and be lost resulting in the shaft being out of balance - if a joint is worn this can also shake them loose

so if a joint is replaced its good practice to have the shaft re-balanced afterwards

Expert:  Matt replied 7 days ago.

Hi

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