I recently replaced my front drive shaft. The old one was shot. Everything was fine. Drove it for months, primarily in town driving. Then I had to take a road trip to Arizona from Texas and noticed a vibration when I got above 70 mph. I also noticed that the vibration was worse under acceleration. I figured, must be U-joints in the rear axel. I had a driveshaft specialty shop in Arizona replace the U-joints and balance the shaft. The vibration was still there. I removed the front driveshaft to try to isolate the issue. The vibration went away. Here's what I don't understand. If the front driveshaft was not engaged, (not in 4-wheel drive, part time or full time) why would it make a difference in the vibration if I was accelerating or coasting? I was also told by the driveshaft place that they did not have the adaptors to balance the front driveshaft. I could order another front driveshaft but I don't want to do that if there is something else going on. Any suggestions would be helpful.

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05 Liberty CRD KJ Limited Sport, Phoenix, AZ
EGR Delete
Nicks Stage 1 Tune
Cummins In Tank Lift Pump
Flowmaster Muffler
V6 Airbox

Have you inspected and replaced the CV joints on the front drive shaft? The front drive shaft is CRD specific and is hard to come by, but the the CV joints are easily to replace. Find parts from driveshaftparts.com
Also, look at the front differential bushings and transmission bushing mounts, those have been known to be bad and transmitting vibration throughout the jeep.
As for why it spins, I think it spins at all times as free wheeling when the front wheels are spinning, thus the front differential, thus spinning the driveshaft. The transfer case gears are neutral to allow the shaft to spin.

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05 CRD; Rebuilt top end w/ARP studs, EGR delete, SEGR, HD cooling fan, Samco hoses, in tank pump, JBA coil overs & control arms, KK clevis fork, 1/2" cradle drop, 1/4" motor mount lift, WJ rear upper trilink w/WW mount, WJ lower control arms, 4:10 gear, front/rear air lockers, ARB bumper, Rock Lizard sliders/roof rack, Mod T-stat

The front driveshaft is new, but it seemed like too good of a deal. I'm thinking you get what you pay for. It didn't vibrate with the old drive shaft and it didn't vibrate when this driveshaft was removed. I'm traveling now and do not have a great selection of tools so I've decided to purchase a rebuilt driveshaft and try that first. If it still vibrates I'm going to remove it and deal with the issue when I return to Texas. I realize that the shaft spins all the time, weather its engaged or not but I couldn't understand why it would vibrate more under acceleration because its not engaged and is not supplying any power to the front axel. I replaced the transmission bushing mounts and the engine motor mounts after I purchased the Jeep. I'll take a look at the transmission bushing mounts. Thanks for your input!

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05 Liberty CRD KJ Limited Sport, Phoenix, AZ
EGR Delete
Nicks Stage 1 Tune
Cummins In Tank Lift Pump
Flowmaster Muffler
V6 Airbox