[beardown]

I know to jack up the jeep and shake the tire but what exactly am I looking for? kinda confused! thanks

 

[daggo66]

Shaking the tire will help you inspect ball joints or hubs. The U joint is pretty much a manual inspection. You are looking for any small cracks.

 

[84554]

Also look for any "Rusty" looking material coming from around the U-Joint caps or the rubber seals... This will mean the u-joint is dry and pretty much ruined...
"BH"

 

[JPi4.0]

Drive shaft u joints: try to move the drive shaft back and forth looking for lateral play in the joint. Then quickly rotate it slightly back and forth looking at the joint for any play.

Axle u joints look for caps spinning. Not much you can do to check them. Maybe move the tire slightly back and forth to see if there is any slop in the u joint.

Axle u joints will usually make noise in 4wd if they are bad.

Drive shaft u joints will usually start vibrating at hiway speeds if they are bad.