The GMC CCKW

Have been working on rebuilding a spare transmission for my CCKW. Picked this one up a few years ago. Does not show much wear, but the unit had been sitting for a long time with water in it, so there were some rust issues on some of the internals.

Replaced all the bearings and a few of the gears - including 5th (overdrive). Purchased an NOS gear, bushing and main shaft sleeve. Made an installer for the new bushing, and pressed it into the new gear. All was going together well, until I tried to slide the 5th gear on to the sleeve. It would not go on. Thinking maybe I distorted the bushing when I staked it into the gear, I made some measurements. The bushing inside diameter was uniform, however the ID was 2.021" to 2.022", which is about 0.005" to 0.006" smaller than the OD ( 2.026") of the sleeve.

Had to chuck up gear in the lathe, and break out the boring bar. After three or four light passes on the bushing, the ID fell into spec, and the gear slid onto the sleeve with about 0.002" of clearance.

I did not see this referenced in any of the TMs. Every one that I read indicated that this was just a drop in replacement.

Has anybody seen this before?

Best Regards...

You say that the replacement parts you used were NOS. This, however does not mean they were made by the OEM. CCKWs were used commercially in huge numbers after being demobbed and many components were remanufactured as original spares became hard to come by. Reproduced parts were not always 100% accurate. I have a couple of unused (and unusable) main shafts on which the spline for the 4th/5th slider clutch is not exactly as it should be and the slider will not go on.
This is a weak area in the five speed box, make sure your oil holes and grooves are as they should be.
I once had a sleeve crack through the hole for the anti-rotation stud. This in turn picked up on the bronze bush and caused the fifth speed constant mesh gear to crack through one of the oil holes. I was 200 miles from home and completed the journey in fourth. If I tried fifth it made a helluva noise.

David

Thanks David.

The part came in a GMC box - but as you say, who knows. Perhaps the supplier they used to crank out replacements parts didn't quite follow the original specifications...

I agree with you on the fifth gear design. Drilling a hole in that hardened steel bushing, then shoving it on over a shaft seems like an invitation to a crack. Surprised they did not make that area of the shaft round, and size it just under the diameter of the third gear bearing surface. Instead of a bushing, they could have used rollers, also like third gear.

The trans that I took out is also very noisy in fifth gear. When I popped the cover off to remove it from the truck, I immediately saw why: Fifth gear must have at least 0.030" radial clearance. I wonder if there is even a bushing left in there...

Best Regards...

Bob