A few weeks ago I just completed a 5 speed conversion on my 84 GL 2 door. Everything seems to be working fine other than this vibration above 55 mph. My initial thought was that the driveline needed to be rotated 180 degrees, which I did and that did help some. During the swap I had the rear driveline extended to accommodate the shorter 5 speed by a reputable machine shop so I'm fairly confident the driveline was well balanced in that respect.

I remember when I installed the 5 speed it seemed like a snug fit in the tunnel, moreso than the 4 speed. Could the tranny be up against the body of the car causing this vibration or should I be looking at something else?

Thanks.......

There should be plenty of clearance in the tunnel. Take the rear driveline out and plug the hole. Trans plug, duct tape, whatever. You just don't want to loose fluid. Test drive it. Vibration gone, take the driveline back. Still there, axle/CV issue.

Removed the driveline and plugged hole as you suggested. The vibration is definitely coming from the driveline. I must say I am surprised, as I said before the machine shop I took it to is known for doing quality work.

Good call skishop, thanks for the help.

Everybody makes a mistake occasionally.