Two seals. One at the universal joint ball and one at the propeller shaft splines. They naturally wear out by motion.
The rear axle on leaf springs can move up and down (pot hole), left and right (curve) , sideways etc. The propeller shaft follows the rear axle. This motion causes the ball to swivel. The rear axle can also move in and out and so does the propeller shaft on splines.
If the ball wears (causes leaks) and forms a rut/groove or rusts badly, the ball can stop moving freely. If the ball stops moving the seal at the splines wears quickly. Tightening the big ring to tighten the seal at the splines works to seal leaks for a time. But there is a limit to how much the big ring can be tightened. Time to fix problems.
The ball joint can be frustrating to fix correctly so many avoid this work unless the leak is severe. Just keep an eye on transmission lubricant level.
A little leaking at the torque tube and engine rear main seal is normal for these old trucks. It's no shame. Use a drip mat.
Last edited by buoymaker; 03/31/20223:06 AM.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
