ramairJP

iTrader: (3)

I noticed a strange vibration on the interstate this weekend that feels like a driveshaft imbalance but is only noticed in 5th and 6th gear at 80+ mph. If I accelerate in 5th at that speed the vibration will practically resonate the entire car, but it doesn't go away by getting on or off the gas. However, I can downshift to 4th and the car is as smooth as silk, so I don't think the pinion angle is off. Could it be something in the tranny, or just a strange resonance with poly motor mounts and the adjustable torque arm? My output shaft seal is slightly dripping, but everything else seems fine under the car. I will make sure everything is tight, but otherwise I'm at a loss. Any help would be appreciated!

DriftR

iTrader: (4)

I had a similar problem, but it is common with the steel LT1 driveshafts not the LS1. Mine did the same... started noticing it at about 80 and above 100 shook the car so much you wouldn't want to go much faster. Looks like you have an M6, with mine I could feel it in the stick. I put in the LS1 shaft and problem solved. Sounds like you checked... but make sure nothing got wrapped around the driveshaft, and look for the tack welded balancing weights?