Hello, And while I am here. . .

New to Jeeps. Dad had an old Willys on the farm years ago. Learned to drive standing on the drivers seat and turning the ignition switch off to stop. Had a throttle set so dad could give it some gas and turn me lose. Now have an 04 Grand Cherokee Limited 4.7 HO with the 247j t/c. 60 cycle vibration at 75 mph. Slight motion at rear drive shaft yoke where it enters t/c. Suspect t/c extension bushing and or rear main shaft bearing. No leaks at seal. Thoughts?

 

Welcome! Just curious....at 75mph could the vibration be due to other issues on an older vehicle (i'm sure you eliminated the ez ones). Does the vibration cycle change at lower or higher speeds?

 

Well, nothing under the Jeep in the drive line assemblies moves at all other than the output yoke for the rear differential driveshaft where it exits the extension housing on the transfer case. If I grip the ujoint at that location and push up and pull down I can get a slight motion of the yoke at the rear end of the transfer case extension. No oil leaking so seal is still OK. The main shaft through this transfer case has two bearings - one front and one rear and the extension housing has a bushing inside just inside the seal. At road speeds, the drive shaft spins at about 60 to 70 rounds per second. That is the freq of this vibration and it is most noticeable, though still rather minor, at 75 mph. Since the yoke is a splined slip fit over the rear end of the main output shaft, any up and down play should be stopped by the bushing in principle I think. Am I wrong about this? It appears the rear bearing, bushing and seal are rather easily replaced, yes?