I put the truck in neutral today and had my wife go through the gears while I was under the truck. I noticed that the driveshaft turned a lot more than I am used to, so I had her roll backwards a few inches (I wasn't under there anymore) so it would take the tensions off the drive shaft. Once there wasn't any more tension on the driveshaft I went back under there and tried to wiggle the driveshaft, it felt solid, so I started twisting it and it would twist maybe an inch or so, but it didn't look like it was twisting via the u-joints (they looked solid) it looked like it was twisting in the differential, and you could feel the gears engaging with a slight almost click noise. I assume that click noise is the pinion gear engaging the ring gear? Is this normal on these trucks? I'm used to a pretty solid feel, no more than an 1/8th-1/4th of an inch of play in a rear end. Not to mention, when it engages into gear it clunks after the truck warms up, but I am thinking that's probably something to do with the transmission.

PS: The rear end does whine a little, but it's not very loud, and it's not anything more than what I've heard out of other older trucks. Almost sounds like a school bus rear end. =) (but, of course, nowhere near as loud)

 

A bit of play is normal, you have to take up the slop in the ring/pinion, AND the spider gears..... the whine might become a concern though....

 

How can I figure out what's whining back there? Pinion bearing, carrier bearing, wheel bearing, etc?

 

Probably your best bet is going to be to disassemble it, and inspect everything.