Ok, I realize I have a drive line or half shaft issue but looking to confirm. Installed the RT diff mount, which made a huge difference! But I am finding an increasing vibration at 3000 rpms and above (gets worse, the higher the rpms). When I let off the gas, the vibration goes away, so is my assumption correct? Anything else I should check? Have an 83 5 speed and R200 diff installed. Visually, don't see any issues with u-joints, but that doesn't always mean anything. Thoughts?

Thanks!

Does it always happen at 3000+ regardless of gear? Or is it only at 3000+ in top gear?

All gears, Arne.

Then the rear end and u-joints are not the cause. If it is always RPM-linked, regardless of gear (or road speed) it has to be in the transmission or engine.

Just a guess but be safe and check crank damper pulley, the symptom seems linked to motor/transmission rpms, not the rear end rotational rpms. It may just be that the vibration is now coupled better to the body with the new part.

parallel processing.

Huh, I am not noticing any pulley wobbling in the engine, and had a complete engine rebuild about 4,000 miles ago. If the engine or tranny are the most likely culprits, am thinking it would be the transmission, as it was installed without rebuilding off an 83 Z and the vibration seems to be coming from the rear. If that is the case, what would cause the vibration from the tranny? Bad gears, etc? What would be the best way of determining tranny issues?

Does it vibrate when revving in neutral? Test with both clutch depressed and not.

Will double check, Arne, but don't believe that it vibrates when revving in neutral.

I checked, no vibration when in neutral and revving engine to 3000+ with clutch engaged and clutch let out

OK, we can eliminate the engine and the transmission input shaft from the discussion. That leaves the rest of the tranny to worry about.

Got any updates? I have the same issue.