Help with scary drivetrain shaking

[soobscript]

I have a scary shake / rattle / vibration / noise coming from somewhere in my drivetrain.

Seems to be speed and load dependent.

The shake has a few different modes / intensities.

The worst conditions are under hard accel and decel with the throttle opened minimum.

Same effects in any gear, but usually worse at speeds greater than 40mph.

Happens thru entire rev range, but usually most scary from 2700-3500rpm.

Happens with and without clutch / neutral, but the shake is different than when in gear.

 

'87 wagon, RX FT4wd tranny, LSD, RX springs and struts all around.

Known problems:

Rear diff top mount bushing is worn. The piece that connects it to the diff (plate with 4 long bolts) only has 3 bolts in use. I've gotten a little clank noise from back there for the last 2 years when changing from go-steady-slow.

Rear-left axle's outer joint has some slop and occasionally grumbles at me.

Driveshaft was replaced with a spare about a month ago. The last one snapped the front u-joint after making increasingly worse shakings for a month. I chalked that up to being from the totaled car in my pic. When I installed the "new" driveshaft: U-joints moved freely, I couldn't get any u-joint play with a pry bar, carrier bearing was an oval shape.

I just returned from a week in the sand dunes where the car was well abused and took many hard landings. Had Accord springs on back for lift at the time. No symptoms were noticed for the 400 mile trip home. (except the wavy bouncing from blowing the shocks - not the ones on car now)

 

What should I be checking?

Driveshaft, tranny mounts, rear diff mounts...

[opus]

I just went through this. Mine was front ujoint almost locked solid.

[nipper]

Yes check the U joints and CV joints. SOunds like a siezed U joint.

 

 

nipper

[soobscript]

Fixed.

 

Rear U-joint of driveshaft.