so while I was under my truck greasing up all the fittings, I noticed that I could turn the drive shaft back and forth, and the wheels didn't move. My u-joints have no play, I could watch the yoke on the rear diff twist back and forth a little. No noises from the rear end while driving. Is this normal for a higher mileage truck? Or should I look a little further into this?

 

it is normal on mine at 350,000 miles.

 

Check U-Joints again.......

 

What you're feeling is gear backlash, and is totally normal... assuming that it's not excessive. I'm thinking somewhere around 5 degrees of rotational play or so on the driveshaft is normal.

 

Like he says. There's supposed to be a prescribed amount of play in the differential gears(aka backlash). That translates to what your describing. Your probably fine if the rear axle has had good maintenance and not been heavily abused. The only way to know for sure is to tear the thing apart and take some measurements of your ring gear & side gear backlash. But you should only consider that if there's a symptom of trouble, ie strange noises/sensations when driven or turned by hand, contamination in the gear oil, things of that nature. Nothing like that going on is there?

 

Nope she is smooth as butter...Both diffs and transmission lube was changed about 50K miles ago. How often should i change these fluids?