Common things to look for include a weight broken off one end of one of the shafts, a bent loop for the u-joint's bearing cups, a collapsed transmission mount and sagged rear springs. The transmission mount and the spring height affect the drive line angle, meaning the angle difference between the pinion shaft in the rear differential and the rear part of the driveshaft, and between the splined shaft in the transmission and the front half of the driveshaft. If the parts are too inline with each other, or too straight, a vibration will occur. Some drive line angle is necessary. It forces the cross to rotate back and forth, and the needle bearings roll back and forth with it. If there isn't enough angle, the needle bearings stay in one place. Indentations form in the bearing cups from the constant pounding. That leads to another vibration.
In some applications the vibration is a characteristic of the model, and can be eliminated by switching to a one-piece driveshaft. Sometimes a service bulletin will direct you to switch from a one-piece to a two-piece driveshaft to solve a common complaint.
The other real common cause of vibration is altered ride height. Raised trucks suffer from this, and along with all the legal ramifications and degraded braking, steering response, and handling, there is no cure except to change how the rear axle is mounted. That gets real involved and still may not eliminate all of the vibration.
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Wednesday, August 16th, 2017 AT 7:54 PM
