Just finished rear engine oil seal, front and rear automatic transmission oil seals, driveshaft center support bearing, and all driveshaft u-joints on my girlfriend's '89 740 sedan 182K. Now there is a rumbling in the driveline that didn't used to be there. It starts at about 45 mph and goes away at about 65 mph. There is absolutely no vibration or shuddering during acceleration, even from a dead stop.

The only things I can think about are:
1. the new u-joints were surprisingly stiff, and were prelubed with what I considered to be thick white lithium grease. I "tested" the u-joints after installation to make sure that they would "flop" downward only under the weight of the yoke, which they did. Do u-joints need to "break-in"?
2. a balancing weight fell off the driveshaft while i was beating on it with a hammer during u-joint replacement (although i didn't notice this)?
3. I didn't reassemble the driveshaft correctly? I didn't mark it but because of the notch in the spline, it only goes together one way.

Any ideas?

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Matt L. -- Cary, NC -- two '89 740 sedans and a '91 740 wagon