1998 Ford Ranger Backlash?

Yes, it does happen in 4wd, but it is not as evident as it is out of 4wd.

Sorry for the delay. OK, with the truck in Park and the rear lifted I was able to slowly turn one of the wheels approximately 20 degrees before making the other wheel turn in the opposite direction. The drive shaft did not engage. Moving to the drive shaft itself, inspecting the way I know how, yokes and u-joints are tight. There doesn't seem to be any play in their attachment. Now holding the drive shaft, truck in Park - rear lifted, I could easily turn the shaft back-and-forth 20 degrees. Very sloppy. I had a friend check my mounts awhile ago because that's what I originally thought it was. In fact, when I bought this truck it had this problem and I foolishly assumed it was the mounts - easy fix. Right - dah!

Once again sorry for the late reply. I took a couple of days off of work to tackle this job. To answer your last question of having play in and out - it does not - at least not excessive. I replaced the passenger side shackle and bushings and while in the process of doing that the entire mount was shot. What a bear! I was hoping that was the problem but it was not. Then under load I saw the rear u-joint flexing even though it was tight to the feel. I replaced that hoping that was it but once again it was not! Then I changed the fluid and popped off the diff cover. The diff was clearly serviced once before. Everything seemed clean but I believe I found the problem. There is a lot of slop in the planetary gears. It appears that the thrust washers are missing or just wore right out. For my Ranger do they sell repair kits or do I need a whole new diff? If I was not to do it myself how much does a job like that run?