So my 91 short bed 4x4 has developed a sqeaking that is in lock step with the transmission (5 speed). It's got a little over 150k on it. It only happens (or I can only hear it) in first or second when there is a little torque on the driveshaft, as in when I am starting out. It dissapears above about 1500 rpm. Sounds like a gerbil running in a wheel.
When the rear is on stands and I turn the drive shaft with my hands there seems to be some play in the pinion, but the u-joints still seem pretty solid, to me at least. I can hear the squeak but not anything like when driving.
I've changed the rear diff fluid and greased all the points in the shaft. Nothing. There are no indications of a leak in the rear diff either. Next I'm planning on replacing the u-joints and maybe the pinion bearings. I've never worked on pinion bearings though. I think working on the diff is beyond the tools and knowledge I have, but I'm wondering how difficult replacing the pinion bearings is. Should I replace these bearings at the same time as the u-joints or is the squeak likely to be one or the other?
Low speeds is when I hear it, I haven't noticed it at higher speeds or when the transmission is slowing the truck down.
Thanks.

 

i would change the u joints first. they r cheap and easy to change. then go from there

 

yeah, sounds like the u-joints to me as well; mine did the exact same thing

the joints feel solid, but they're probably dried up

what happens when you use reverse? I'll bet it's louder sounds like a classic u-joint failure

 

yeah, figured I'd start with the u-joints and go from there. Just didn't know how much, if anything else that would be cheap that I'd be able to do while the driveshaft was off.
Thanks for the responses!