Closed Driveline Torque Tube
One of the most misunderstood parts on early Chevys is the closed driveline torque tube. Over the 40 years we have sold parts for these vehicles, I have come across dozens of restorers and professional mechanics that do not understand the basics of adjusting & maintaining them.
Closed driveline manual transmission U-joints from 1929-1954 Chevrolet passenger cars & 1/2 ton trucks are designed to be lubricated by GEAR OIL only. Do not use grease! Most transmissions have a separate fill plug at the rear above the U-joint ball housing. This plug is to fill the ball housing after assembly. Some transmissions without fill plugs must be filled through the speedometer drive gear opening. YOU MUST MANUALLY FILL THE BALL HOUSING WITH GEAR OIL - DO NOT RELY ON THE GEAR OIL IN THE TRANSMISSION TO FILL THIS HOUSING. IT WILL BE TOO LITTLE, TOO LATE!
A common misconception is that this type of U-joint must be tight, if not, it is bad, Not So! Actually, closed driveline U-joints are supposed to be loose to allow clearance for gear oil lubrication. For this reason, checking the fluid level in the ball housing is very important when doing regular maintenance on your old Chevy. To be clear, sideways movement is to be expected and is normal. However, torsional movement - that is when the front and rear yoke are twisted against each other - is not acceptable. There should be very little movement when it is twisted back and forth. This would indicate a bad U-joint.
To check the U-joint, disassemble the rear yoke from the front yoke. Inspect the trunnion (center cross) and bushings for wear. The wear will be obvious in a bad U-joint assembly and most noticed at the studs of the trunnion. A common cause for a bad U-joint is lack of lubrication. A U-joint repair kit will replace everything except the front and rear yokes.
Another cause of U-joint or bushing failure in our old Chevys is gear oil running down to the differential because the seal in the torque tube is no longer doing its job. This seal is supposed to keep gear oil in the U-joint ball housing to lubricate the U-joint and torque tube bushings. When this seal fails, gear oil in the ball housing will run down to the differential. This has bad effects - it overfills the differential, lowers the gear oil level in the transmission and can cause the rear axle seals to leak. It also causes lack of lubrication where it is needed in the U-joint area. This allows friction and heat to build and destroy the bushings and U-joint components. Installing a new bushing & seal assembly will resolve this problem.
Check the torque tube drive shaft bushing for wear. This bushing is located at the front of the torque tube where the rear yoke slides into the tube. The bushing can be checked, after the U-joint is removed, by grasping the drive shaft at the spline end and move it up and down within the tube. If there is ANY movement of the shaft within the outer tube, the bushing is worn out and should be replaced. A bad bushing will cause driveshaft vibration and can cause U-joint and seal failure. New bushing and seal assemblies are available for most 1916-1954 passenger cars & 1/2 ton trucks.
Install a new U-joint gasket set when you have the U-joint apart for maintenance since this is the only way to get the gaskets in place. Refer to the shop manual or our tech article: https://www.fillingstation.com/articles/universalball.htm for proper adjustment of the U-joint shims when installing new gaskets.
After installing the U-joint, fill the ball housing with about 1/2 pint of 80-90W (1936 or earlier models use 600W). Fill through the top plug at the back of the transmission or speedometer drive hole. FAILURE TO PROPERLY LUBRICATE THE U-JOINT CAN CAUSE SERIOUS DAMAGE TO THE DRIVESHAFT BUSHINGS, U-JOINT AND TRANSMISSION HOUSING.