The Stovebolt Site Forums The Shop Area Driveline Rebuilt transmission jumps out of 3rd gear - Bad Rear ?

Was tracking down a rumbling, grinding sound and feel on my 3100 1/2 ton truck last year.
After replacing pilot bushing, flywheel, clutch and throw out bearing, I found what was thought to be a rebuilt 3 speed transmission.

Shifted like new into all four gears, but got increasingly noisy with rpm and jumped out of high gear around 2000 rpm consistently.
Had one 'high gear jumper' transmission many years ago, but it only happened occasionally and I could hold it in gear easily by holding down the gear shift lever.

This one really wanted to drive out of gear and no force could hold down the level and stay in gear.

Eventually I figured out what the grinding, rumbling noises were all along.
Both pinion bearings of the rear end disintegrated.
This after I had the ring & pinion upgraded to 3.55 in 2000 by a pro trans and rear gear specialist.

So now I wonder, is it possible, if you have failing rear end pinion bearings, that the transmission would jump out of gear around 2000 rpm in high gear?
Is that transmission actually good or really needs repair?

Thanks for any help.

Bad pinion bearings would not have anything to do with the trans issue. There were several upgrades to take care of the clutch gear jumping out of gear. In 1953, a revised clutch gear and main shaft was used with double set of needle bearings to eliminate this issue. Try looking for a good used 53 or 54 transmission for a direct fit. I assume you are still closed driveshaft correct?

Cool, Thanks - I already have another transmission that was rebuilt 15K miles ago.

Yes, torque tube - in fact I have a Wanted ad in the classifieds for one, hoping I don't have to completely rebuild my rear gears.