I took it to a shop that took the driveshaft out and ran the motor to find the vibration. They said the drive shaft was too long and that with flex it the whole system it could slam the rear end.
Was told by Republic Diesel(makes drive shafts) how to measure the length needed. Take the U joints loose in the rear and push all the way I can into the tranny. Measure from center to center of joints. Then they figure less 3/4". Did that, current shaft was correct, then took to them to put in new U joints.
Still have issue. Thinking that between the front motor mounts and the current tranny mount, I'm getting a slight twist causing the vibration.
