Fourtrak Transmission & Sportrak Misfire?


My 92 2.8TDX (leaf sprung) Fourtrak/Rocky has developed a grinding / beating habit in 5th gear. Transfer box is an unreconditioned breaker box after an accident last year. Its always been a bit rough but I was wondering if it is the main shaft bearing that is on the way out this time. The vibration kicks in if I go over a bump in 5th and I have to back off the power and rev up again to keep it smooth. Also if I engine brake in 5th I get the same. I guess its either 5th on the way out or the main shaft. the whole transmission is a bit iffy above 2700 revs anyway.
Any ideas before I start a major removal and strip down job?

The 2nd problem is my girlfriends 91 petrol EFI sportrak. Its got a severe flat spot between 2000 and 4000 revs. Feels a bit like the misfires my old citroen had when the coil pack was on the way out. Anyone had this with a sporty or know of a/what to fix.

Thanks people

flat spot on sporty

had the same problem changed the distributor cap, rotor arm and HT leads, problem solved running better than ever. HT leads may not have needed changing but they were looking a bit worn.