In my 1982 w123 300CD.
New tires, good, tight suspension, no steering wheel play.
Tires (15” bundts with 195/65r-15 Cooper CS5 Ultra) we’re roadforce balanced. One is showing 34# of roadforce balance, the rest are all 8-12#. Tires all roll smooth, the one that’s the worst is the drivers front tire, and there is minimal to no shimmy in the steering wheel. Car tracks slightly to the right, but the tiniest bit of adjustment keeps it straight and true.
Tires do not appear to be wearing funny.
At around 40 mph, I feel a rumble and vibration from the floorboard/seat. Minimal to none in the steering wheel. Harder to notice when at faster speeds. Sometimes more notable when decelerating.
Using a vibration meter, at 60MPH, and knowing the tire revolutions/mile, I can see that the third harmonic is as bad as any tire motion. Usually tire motion (14Hz) should be way higher.
This points to the driveline leading up to the diff.
So I took a look underneath this afternoon. Everything looks straight and perfect.
I had done subframe bushings last year:
Squeaky subframe bushing
Diff mount looks good:
As does the driveshaft:
As does the csb as far as I can tell. Can’t really shake the driveshaft and get any motion out of it.
I guess I could get it up while on the kwik lift and cause the wheels to spin, car in drive. Maybe have a helper take it to 40 or so and see. But what else should I be looking for? Is the best bet to just remove the driveshaft and check things from there, with it out and able to be moved independently?
Thanks!