Been trying to figure out the intermittent vibration I've had in my 92 XJ. At 50 to 75 mph I get the 'dadadump' vibration every few hundred feet down the road. More in seat/floor than in the steering wheel. which leads me to believe: rear diff. No whine, high pitch or loud grinding that is normally assoc with a very bad bearing issue though.

Spinning the tires by hand, all was quiet.
Pulled the tires/ drums off and cked the axles for play etc.
There is only bout a mm of play up/down or side to side. They feel tight.

When i spin each side its definitely not smooth but not super rough. It's enough that you can feel it as you spin the axles- more so with the right than the left.
In addition when i spin the left axle clkwise / ctr clkwise, it's alot easier, and feel it engage the spider gears like there is a tiny bit of play. The right axle is tight when doing the same quick rotation.
Is that the nature of the stock Diff since it is not a posi or aftermarket limited slip rear ?

At 217k I feel it's outer bearing time but hope it is not more than that. Driveshaft U joints are solid. i do have a little hum but nothing very loud. Frnt hubs, linkage etc all ck out good. Possibly transfer case hum but could be those rear bearings as well.

To future proof myself if they are needed:
Sourced out a parts XJ nearby, Will axles from a D35 3.55- '96 XJ w/ auto trans fit my '92 D35 3.07 w/ 5 spd?? I believe mine our 27 spline axle.

 

If I have two wheels a tad out of balance, it might role smooth while they cancel out, then I'll feel it when they get in sink. The result is a viberation that comes and goes. Sort of sounds like yours.....

 

That's an interesting concept and very believable.
I'll go get them balanced and see how it feels before I dig in.

 

SOLD! to the bidder in the Sturac shirt..next up for bid...

 

Can't pick up that tab just yet Dflint.
Got the rears balanced and get different vibration albeit less but between the front tires being a bit scalloped and the suspect rear I don't know which way to go,
I don't have a lot of cash to burn just attacking and replacing as I go hoping that will solve it. Sure would like to replace many parts suspension wise but am trying to be thrifty and efficent at the same time.

But back to my main question :
When you spin the axles (w/ tires off, neutral trans) is it supposed to spin very smoothly while your hand is on the hub or is there some small vibration due to the gears turning ?
I'm at a loss here.

 

Maybe someone else's memory is better than mine. I suppose I would expect it to feel pretty smooth.

Me thinks since the ring gear remains stationary, (while in gear), and just the spiders spin, it should feel the same.

 

What condition are rear tires in. Is it possible two swap a set from the other xj and ride it around a little thus eliminateing tires maybe . And as long as both axles are c clip they will swap .

 

At 50 to 75 mph I get the 'dadadump' vibration every few hundred feet down the road.................. A rear axle spins much faster than tires seeing a few hundred feet as you say here id suspect tire issue .