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Drive line vibration / aligning your drive line

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    Drive line vibration / aligning your drive line

    Maybe this will help someone else down the road.

    I disconnected the driveshaft at the flex disk, and unbolted the center bearing so I could move the driveshaft out of the way in order to rebuild my shift linkage and install a short shift kit. At the same time, I replaced the worn transmission mounts (read as: I moved a lot of stuff around).

    After reassembly, I like the feel of the new shifter, short throw, much tighter shifts. However, I picked up a drivetrain vibration that came in about 45 mph and really amplified at 60. I was thinking that after moving the driveshaft I over-stressed the u-joint or center support bearing.

    The car goes back up on the jack stands, the rear half of the exhaust comes out and the shields off to inspect the driveshaft. The flex disk looks good, the u-joints fine and even the center support bearing looks like it’s in good shape. All the nuts and bolts are tight. Off to spend some time with Mister Bentley.

    A few on-line posts and the Bentley manual reference the importance of driveshaft alignment. Rolling back under the car I can’t find a good reference to measure along the length of drive line to ensure the entire drive line is reasonably straight.

    After much head scratching, I resorted to good old gravity. I took a length of string, with a loose loop around the driveshaft with a fishing weight to hold the string straight. Having the AC belt already off, I put one string on the crank shaft, one just behind the flex disk, one just behind the center support bearing, and one in front of the rear u-joint. This gives you the ability to eyeball the entire drive line. Mine was all over the place. It took me about an hour to maneuver the various mounts around to get a straight line.

    The vibration is gone!
    2004 525i Manual - 1985 325E Coupe Manual
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