Hi Folks, first post here. SM420 4 speed transmission, oil leak at cap behind ball joint. My question: if there is a oil seal on the rear of the trans, and a oil seal on the torque tube how is the u- joint lubricated? Also, maybe some insight on which may be leaking. Thanks! Jon
What model truck do you have and does it have a torque tube?
Phil Moderator, The Engine Shop, Interiors and Project Journals
1952 Chevrolet 3100, Three on the Tree, 4:11 torque tube Updated to: ‘59 235 w/hydraulic lifters, 12v w/alternator, HEI, PCV and Power front Disc Brakes Project Journals Stovebolt Gallery Forum
U joint lubricated by oil from transmission no seal at rear of transmission, gaskets sounds like your leak maybe at the ball or collar.The collar can be tightened up they do loosen.
I have a '46 1/2 ton with the old style non synchro'd 4 speed. That sucker ate U-joints until about 10 years ago, when I started using about 5 oz of W140 gear lube in the small pipe fitting on top of the U-joint at the rear of the trans every 300 miles or so. I can see no evidence of the U-joint getting any lubrication from the trans. If I don't do this lubrication, the truck develops heavy vibration that is coming from the U-joint. As soon as I lube it, the vibration stops. When I go on road trips, I carry a small pump can and will hit it on the side of the road. The extra lube ends up in the transmission, somehow, and it's frequently overfull when I add the U-joint lube - I just drain off the excess. Not a great solution, but it's worked for me for over 20,000 miles and I haven't had to change out the U-joint. Would love a permanent fix, but I've heard from many folks that the U-joint is the weak point in the torque tube system and was frequently a problem.
