Background:
91’ Hardbody V6, 4wd, KC with a 2-piece drive shaft with about 120,000 miles. I have always used GL-4 oil in it. The first synthetic oil I used (NEO) claimed to be both GL4 and GL5 approved but I see that they are now selling them in two bottles, one for each type. I have been using Redline for a few years and overfilling since I first saw the post about the oil level issue.

Problems:
1. I’ve had driveline vibrations at low speed under acceleration since lifting the rear. It has gotten a little worse lately. I know this is bad for bearings and seals in the rear.
2. I believe the center bearing is going out (again) and the center u-joint is a little loose. I can slide it back and forth between the end caps. All hardware is tight.
3. Shifting is notchy, especially at low speeds. This has been getting worse lately. If I don’t shift slowly, pausing slightly between gears, they grind.
4. Jerking and shuddering when first taking off, forward or reverse. I believe I got oil on the clutch years ago while trying to get the clutch fork to stop squeaking. I have bled the clutch hydraulic system several times and replaced the slave unit. I’m going to replace the master unit soon.
5. The latest problem is a faint whirring noise at high speeds. I can only hear it in 4th and 5th gears at highway speeds and only with the windows up and radio off. It goes away when I let off the gas. I’m thinking this could be the center bearing.

I’ve got the SYE but have been hesitant to install it after reading of the problems people are having. I will be going to a one-piece drive shaft but wanted to wait until I get the axle the way I wanted. It’s a daily driver during the cold season but here in SoCal I can ride my bike almost any time if the truck is down for a while. I can easily replace the u-joint and center bearing before the AZ run. I might be able to get a new one-piece drive shaft made but I would have to replace it or have it modified if I change out the rear axle. A new or rebuilt tranny is on my list of things-to-do.

Any comments or suggestions? Do you think I will need to repair the tranny?

You should have a 1 peice driveshaft made for your truck. It'll run you around $200 and will eliminate the CSB problems. Just take the whole mess into any DS shop with the tcase output to pinion yoke measurement and they can put a new tube on what you have to make it a one peice unit.

Sounds like normal tranny wear. The synchros are wearing, and possibly some bearings are too. It probably still has some life left.

The chattering clutch tells me you might need a new clutch disc. Maybe it had a hot spot on it.

Ujoints - easy to replace. Those or the carrier bearing are the cause of the vibration, assuming your tires are balanced well.

Why again are you wanting to swap out the rear? It's a geared and locked H233B.

"I can only hear it in 5th and 6th gears at highway speeds "


6th gear?

Ok, ok, it's a 5 speed!

DR, I am considering replacing it with a different axle. Not sure I'm going to, but if I do the new one piece drive shaft would have to be replaced.

All of these problems except the whirring noise and the loose u-joint were present during last year's run, just worse now. I think I'll just go with the one piece driveshaft just to be sure I don't start anything that can't be finished before this year's run. I already priced a new tranny/clutch/flywheel through ABC. I don't have the know-how or tools to rebuild it myself and I don't know of any shops around here that I trust to do the work, especially right before a run. I did the crawler gears by myself so I think I swap out the tranny without too many problems.