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Season's greetings!
I just finished test driving my sister-in-law's '90 740 to verify that her freshly installed rebuilt AW transmission is working correctly, which it is.
However I also noticed a moderate-severe vibration in the car at around 2,000 rpm, noticeable in the transmission lever, less so in the wheel but still there.
With the vehicle in neutral and stationary the vibration is also present, again at about 2,000 rpm. I did not try revving the engine further to see where another node might appear as the problem is amply bad at 2,000 rpm.
There do not appear to be any ignition or fuel delivery problems. Acceleration is as good as it ever can be with this 8 valve normally aspirated engine.
The vehicle has 317,000 miles on the clock, has been scrupulously maintained.
Searching B-B, I see that harmonic damper issues may appear as a squealing noise when the rubber segment slips.
I also see that this sort of vibration may indicate a crankshaft bearing problem. I would have imagined that an oil leak would accompany a bearing with so much throw in it. This car is dry as a bone leakwise but perhaps my intuition there is wrong.
Does anybody happen to know if a failed harmonic damper is likely to reveal itself by a vibration as opposed to squealing/slipping problems?
I'm hoping I can tell the owner to try the damper first. The timing belt is due in another 10,000 miles so going in to do the damper would not be too horrible. Crankshaft bearing of course is another, sadder story...
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