The Stovebolt Site Forums The Shop Area Driveline U-joint alignment on 1939 JD pickup

What is the proper alignment procedure for the U-joints on a '39 JD pickup? When I place the u-joints on the shaft with both parts number on same plane, there seems to be about a 1 or 2 degree difference. How important is this?

Thanks

Gary

There should be no misalignment at all- - - -it sounds like you've got a slightly twisted driveshaft tube. You could encounter an annoying vibration at certain speeds that will be impossible to correct.
Jerry

Jerry,

OK, tomorrow, I'll finish tearing it down to see what I can see. I will first do a better job of eye-balling it...or use something proper, and not just my eyeballs. Did the idea of placing the parts number on the u-joints on the same plane make sense to you? If I phase it 90 degrees, it's completely out of whack.

Thanks

Gary

I would suggest getting hold of a couple of level vials, or maybe a machinist's combination square with a head that can be rotated to a specific angle. Block the shaft or hold it in a vise (gently) so a vial on one U joint is level, then use the rotating level head to check the alignment of the other one. I assume the shaft is the open driveline type with a Cardan-type joint on both ends?
Jerry

No, it's the closed driveline with the u-joints close together immediately behind the transmission. I'm going to pull the u-joint that's attached with a bolt (the rear joint), and play with the splines to determine if there might be a proper position for the joints on both splines...not tomorrow, but maybe Wednesday.

I can come up with some sort of jig to properly align them.

thanks,

Gary

Hmmmm- - - - -we're not talking about a Chevy, then? What's a "JD"? All I can think of offhand is John Deere, and I don't think they made any pickups.
Jerry

JD is the 1939 model symbol/code.

Correct. 1939 JD 3/4 ton Chevrolet pickup with enclosed driveline. The propeller shaft is enclosed, and runs from the differential to about 1 foot short of the transmission. Then there are 2 u-joints connected by a short shaft (also enclosed) support by a crossmember mounted fixture. The u-joints are separately enclosed in bell shaped fixtures. The u-joints are lubed from/with the transmission fluid.

OK, I had forgotten about the half-shaft type setup on the 3/4 ton. If you can get enough access to the U joints to get a level on one or both of them, that's still probably the best way to check the phasing. The joints should move in the same plane, as any angular difference will cause them to run in a bind somewhere around the circle, probably twice.
Jerry

Jerry,

I have the u-joint assembly out, and on the bench. One of those deals where I'm fixing stuff I didn't do well the first time around. They are tricky to set up properly to keep the oil from oozing out. I have to bust them down more to get a better handle on what might be the problem. I do appreciate the effort and input.

Thanks,

Gary

When I ran a Diesel repair shop and road service, I encountered more than one twisted driveshaft, the result of a driver getting a little too energetic trying to get a heavy load moving. Rev the engine up and dump the clutch in Granny gear, and something's going to move, bend, or strip out. These old rigs got used and abused a lot before most of us acquired them, so anything is possible. I've got the remains of a 51 GMC running gear that might have the same intermediate shaft, if it would interchange with your assembly. I have no use for it, as I acquired the bare frame and part of the running gear in a swap. Got any pictures available? If so, drop me an email.
Jerry