Incorrect Rear Transmission Mounting Bolt Length
Installation of the rear transmission mount rear bolts that are too long will cause the bolt to contact the chassis and transmit noise and vibration directly to the chassis negating the transmission mount vibration and noise dampening ability. There should be a minimum of 1/8″ between the threaded 1/2″ NF bolt that secures the mount to the transmission tail shaft housing and the chassis rail.
It is not un-common to find the gear shift housing stiffening bracket and distance piece, as fitted to the right side of the rear mount, missing and the extra length bolt used with this bracket, installed. This condition is further compounded by softening of the rear mount in service and sagging of the rear mount. Correction is by reinstalling the bracket and distance piece or shortening the bolt(s) to avoid direct chassis contact.