I have a vibration at 45 mph that I can't figure out its on my 98 expy 4x4 102,000 miles automatic tranny. last march I changed all 3 u-joints in the rear driveshaft and still had a vibration, I tried to get a rebuild kit for the centering ball and could not find one even through Ford, so I removed the driveshaft again and took it to have it rebuilt now its doing the same thing but this time at 45 mph not 65mph.

today I changed the rear u-joint thinking this was the problem because I could sense some play in it only this time instead of a hammer and socket I used a friends snap-on u-joint tool to press them in and out, the vibration is still there.

should I change the other 2 u-joints also, even though I don't sense any movement in them?

could a wheel bearing cause this?

when installing the rear driveshaft the 1st time I am not sure it is in the exact location as when I took it out could this be the problem?

could there be a problem in the tranny or transfer case?

could it be in the rearend?

thanks for any help I know it is almost impossible to diagnos a problem like this online but I am hoping someone else has solved this on their expy.

 

This sounds very familiar to me. I also have a '98 XLT with same symtoms you had mentioned. In addition, I also noticed the "vibration" seemed to suck a good amount of power away from engine and noticed a small amount of fluid under vehicle after parking overnight. Now the bad news....
Took it to Ford due to still under warranty. They found the tranfer case to be problem. Apparently the bearing (entrance?) would seize at higher RPM, then overheat, that caused the aluminuim case to crack (fluid leak). Due to cracked case. they replaced the whole transfer case under warranty. This would be a VERY expensive repair without coverage.
Sounds like you are able to due quite a bit of work yourself, so check the bearing on front end of tranfer case.
Best Of Luck..

 

Check condition of tranny and transfer case mount bushings and bolt tightness on mounts.

You did mark the flanges on the drive shafts at both ends of the joint before taking them apart didn't you?

Rotate drive shafts 1/4 turn and try. If still there rotate another 1/4 turn and try again. If that doesn't do it repeat.

 

thanks for your help guys. I think I have found the problem today I took the skid plate off from under the Tcase and was pushing and pulling on rear of tcase and found that the housing that seems to be in between the tranny and tcase is cracked and loose. I am sure that is not helping the situation at all.

so my next question is has anyone ever pulled their tcase and if so do you have any pointers for me. I have one of the manuals you can by ie: chiltons not sure wich one and it will help I'm sure but I could always use first hand accounts.

 

for those who might care I pulled my tcase and the tranny extention housing was cracked clear through, this is the part that extends of the back of the auto tranny and bolts to the front of the tcase this is all that supports the tcase and with only 3 bolts holding the tcase up it was causing my ujoints to fail and the vibration, you guys might want to check yours just to make sure .