Missed this when it was originally posted, had the rear axle had been dunked in mud/water at some point in it's life??
Were you able to ( @Killdozer1776 ) replace the emergency brake components and rotors, service the hub bearings/seals, etc, etc? Got photos?
Check your brakes (pads, calipers).
Check that your brake pedal return spring is in place (long shot, but if that drops out, IME, your brake pedal can be pulled down by the booster as if you're pressing on the pedal/brakes). While driving if that happens you can get a significant vibration that...
Assuming you're driving a US spec FZJ80 you should find another mechanic. There are no clutches in either an open differential (K292 axle code) or locked diff (K294).
There was a 80 series model that came with limited slip diffs (K293 axle code), but those were not imported into the USA.