my 85 has some drivetrain noise and we cannot figure out what it is. some people say transer case, others ring and pinion, others axle bearings. its just a whirring sound that builds up at about 20 mph and only when accelerating, it goes away off the throttle. what could it be?

 

With that description, sounds like you have all the suspects lined up. What transmission you got? An axle bearing would progressively get louder. Most ring and pinion noise comes in at around 35mph under light throttle. The transfer case chain doesn't turn in 2wd. Hope this helps.

 

It would be slop in the pinion. You might be able to get by for while by tightening the pinion nut to about 15 inch lbs pre-load with the hubs off.

 

alright guys thanks. that what i said about the transer case to my pops, but some mechanic told him it might be that (should be fired) and the previous owner said it has made that sound ever since he got it, about 10,000 miles ago. its the 4 speed with automatic overdrive. and the previous owner said when he rebuilt the trans he also pulled the axles and put new ones in, but he cant remember if he put new axle bearings in. the first thing i thought it was some slop in the ring and pinion. would a new ring and pinion solve this? thanks guys

 

The ring and pinion are more than likely OK. You could do what I said above or replace the pinion bearings. The pinion is moving some as you are accelerating and letting off. The noise is coming from the miss alignment of the ring and pinion gears when the pinion shaft moves.