For the last few years my cherokee has been making this rythmic humming/vibration between 50 and 60mph mainly, it's now started to happen at much lower speeds and becomes unbearable at 60mph. I've just swapped in a junkyard rear axle+diff and it seems to be worse than the O/G axle/diff I just swapped out.

The vibration seems too harsh and noticeable under the footwell to be caused by the rear diff. My gut tells me my O/G torque converter may be the culprit, or possibly a new front driveshaft that's out of balance? Could it also be that my transfer case/transmission is the culprit?

I've only just started to get really detailed on the driveline side of things and trying to learn as much as I can on here since Egyptian mechanics seem to swear by folklore and old wives tales instead of actually diagnosing anything properly/methodically. Any help is appreciated!!

 

Did you try removing the front drive shaft and see if it goes away ? and do you have a one piece or two piece rear drive shaft ?

 

I tried removing the front, it helped a bit but not completely, so I swapped my front DS out for a junkyard DS that was in way better condition, changed the u-joints and still I have the same issue but worse! My rear DS is a two piece, I plan on ordering a frame stiffener kit, SYE and new driveshaft as soon as I possibly can. Could it be that my rear pinion/diff is so bad that it is causing all the clunks and vibrations through my driveline? Visual inspection just ain't showing much other than obvious slop in the driveline, especially when engaging drive or reverse....

 

Put it up on jack stands and run it to see what is vibrating .