Rig:
87 4Runner 22RE 5spd swap with a W56

Situation:
Had a W56 in it for a while, had to change the rear main seal, dropped the trans. Then decided it was easier to throw in my spare (working condition) W56 in rather than change some more seals. (Trans-to-t-case leak)

Problem:
Rear main fixed, "new" trans in, now when I start it, I get a "Thunk" sound and feeling in the truck as soon as it starts. The thunk is only audible in the cab, as well as the thunk feeling.

I torqued the flywheel, pressure plate, and trans to spec. Starter is fairly new, maybe 2 months on that. I did put in a different rear d-shaft, out of a 2nd gen (length is perfect now).

This happens when starting it with my foot on and off the clutch.

The truck drives fine, small humming sound in 3rd (like the hum of mud tires).

Dunno what I did wrong here? Did everything I did when I put the other 5pd in before and never had a problem with it.

I'm at a loss...

 

Nobody