We have a 1998 Ram my husband just replaced the u joint at the wheel hub. the new joint has a grease fitting in one of the caps. he is getting a violent shake at 55 MPH that dosn't seem to go away as he speeds up, what do you think could cause this

 

driver side? and its the u-joint in the stub shaft to inner shaft?

 

passenger side at the wheel hub, we pulled the shaft out from the CAD unit. he said it isn't vibrating as bad today. but still vibrating.

 

Not installed correctly? What was the original reason for replacing it? Did he grease it?

 

^Ya, maybe it's not seated properly. Did he do it himself or take the shaft somewhere? It's gotta be able to move around a LOT each way, if he did it wrong it will be tight to move. A lot of times it can be tight and make no difference in a rear driveshaft, but an axle shaft is different.
Could also be that there's a piece of rust behind the rotor, that happens a lot.