driveshaft play

I'm trying to track down a rear end noise that just came up recently. It's an oscillating noise that is noticeable when decelerating. On accelerating, you can hear something like a bit of a grind but it's very slight. I poked around and noticed my driveshaft on the tcase end has some play. I wanna say maybe like 1/16th of an inch. Same for when rotating the driveshaft back and forth. Is this normal? I checked the u-joints and although they're very old and probably were the original joints from the factory, they seem pretty solid. No slop from where I can see. Any ideas? 98, 5speed, 4.0L

sounds like driveshaft issues, notable the ujoints.... thats exactly what i had at the tail end of my oem driveshaft ujoints... bad vibration on decel, a general 'not right' vibe, and a loud clank when shifting from rolling in reverse, to driving forward (the ujoint going from one direction to another with slop)

you shouldnt feel ANY slack at the driveshaft... it should feel like theres weight on it, as-if to spin it means moving the truck forward of back 3-4". did yo pull the driveshaft to check the ujoints? mine was obvious, but even 1/16 is too much.

A little bit of play in the output is normal (especially in-and-out, since the slip yoke is supposed to move in-and-out). First thing I would do is replace the u-joints, and grease up the slip yoke. If you still have noises, put the rear end on jack stands and listen with the truck in gear

I didn't pull the driveshaft yet. The driveshaft doesn't have any in or out play, just up and down on the tcase side. Rotational play of the driveshaft seems to be from the differential itself. The pinion spins with the shaft. I'm no expert on differentials but reading the threads on setting up one, one would think it should be tight. Regardless I'm changing the u-joints and hope it'll solve the issues. I just hope it's not a pinion bearing because the noise sounds like rough bearings.

there should be NO play in the pinion itself... if there is play at the pinion u-joint then there's your problem

lots of things make grinding noises... put it on jack stands and listen

There will be some side-to-side, up-down play at the slip yoke into the TC. The yoke is just a slip fit (hence the name) over the splined output shaft in the TC. There is a bushing (a thin metal sleeve, really) that rides over the outside of the yoke. That bushing can wear out but 1/16" doesn't sound abnormal.

If you are getting grinding noises, I would pull off the DS and take a look at the output shaft and the yoke. Make sure there is no evidence of abrasion or rubbing. Before you reassemble pack the inside of the yoke with grease.

There should not be any up-down or side to side play at the pinion, however. If you can feel play here that inidicates a worn pinion bearing. Bad bearings here are usually accompanied by leaking from around the pinion seal, so if you're worried about this clean off the front of the diff housing and monitor it for leaks.

Rotational play in the drivetrain is called backlash and is normal, to a point. It comes from the spaces between teeth on the differential gears. The amount is small on new gears and increases with wear, but usually isn't a problem.

What you don't want is rotational play between driveshaft compenents. There should not be any play between the DS and pinion, or between the DS and slip yoke. That would mean bad u-joints.

Besides all of that, is your DS geometry OK? Are you lifted at all, have extended shackles, or anything of that nature? Is the DS balanced (maybe a weight came off)?

Have you checked fluids in the TC and differential?