Not so good vibrations

[Rackne]

Some time ago I brought up a thrumming sound that runs through the length of my car (72 108 4.5) at highway speeds. A carrier bearing was suggested as the culprit, I just spent the balance of my free time over the past three days replacing the culprit. And although the bearing was dry as a bone and rattled like a maraca, the car still has the vibration. In addition it has more severe vibration at around 40mph that goes away as speed increases, any suggestions? The alignment and front tires are recently done and the vibration occurs regardless of which set of rear tires I have on it.

loose wheel bearing? Also, I had warped break disc on one of my cars which gave a similar sound?

[Aaron]

Sounds like a driveshaft out of balance to me. Rather common occurrence with 108s.

[Tom Drew]

Am experiencing a similar unexplained vibration in my 108 as well, although more subtle than Rackne's. Aaron, what is the procedure for checking a driveshaft for proper balance? Am I correct in assuming that the shaft has to be removed and sent to a speciality shop for balancing? Please enlighten me!

[Rackne]

Yes, enlighten us. Assuming that the shafts will have to be balanced simultaniously, will this take a specialty shop or can the average driveshaft place do this? (Average driveshaft place? I'm in the middle of Toto-Land, where my parts store had never heard of a flex disc, fuel injector points, etc., and I'm asking about an average drive shaft place.)

[Arthur Dalton]

Small off balance can be countered with washers at different positions on the flanges.
But don't overlook the motor mounts. They will fool you.
Rear view mirror blury ?? Tingle feel in the steering wheel ??

[Aaron]

A driveshaft shop will be able to take care of this procedure for you. You have to remove the shaft and take it to them for balancing. They will generally offer a rebuilt/exchange unit.

[Rackne]

Well I drove the 108 down to Norman OK over the weekend, about 600 miles round trip and it performed excellently humming all the way. I'm thinking that the driveshaft balance is the culprit and will get to it when I replace the flex disk. There is of course the small matter of convincing the guys at O'Reillys that the flex disk exists but thats just part of the charm of the place. I really enjoy travelling in this car, it doesn't raise the hackles of the authorities the way my old camaro's did. Instant respectability!