Driveline vibration...

[bealaddison]

I have a rear driveline vibration that starts @ around 50mph while accelerating and diminishes as you accelerate past 60. Let off the throttle and coast or just give it enough throttle to maintain speed and the vibration goes away. My ride is '87 Suburban with 6in lift and 37in tires. I recently swapped in a sm465/np205 combo. Prior to that it had a 700r4/np208. At the same time as the trans swap, I changed out the rear axle from a semi float 14bolt to a full float 14 bolt. I also got rid of the rear leafs/blocks combo and installed a set of 6in lift springs.

I realize that is a lot of parts to swap at once and chasing this vibration down will not be easy. I was just hoping to hear some opinions and narrow it down a little. I checked transfer case output shaft angle and it is around 5deg down. Pinion angle was around 1deg up, so I installed 3deg shims at the axle, making it 4 deg up. I had the vibration before and after installing the shims. Not much change.

I am also running a conversion U-joint, 1310 to 1350 at the pinion. Prior to install I had the driveshaft shortened and balanced by a driveline shop. Transfercase output is a fixed yoke with the slip yoke in the driveshaft.

Axle and trans seem tight. I believe I am chasing a working angle issue or driveshaft imbalance. Anyone want to offer some ideas?