98 expy 2wd

i've been chasing various vibrations on this truck. i got the front end fine now, but there was still a vibration in the rear. i had the rear tires balanced, but no better. i thought the u joints went bad. they seem fine but i did notice that where slip yoke enters the trans housing, the shaft wabbles a bit and there is some fluid oozing out. i can actually move the shaft/yoke a bit side to side. also, this yoke is different from anything i have seen before. there are no shackles or flanges on the front half where it enters the trans. the yoke shaft itself appears to go directly into the trans. i assume there is a bearing/bushing in there. can this be easily fixed? does this require a trans rebuild?

any ideas are appreceated as i need this truck for deliveries for my job and put on 1000 miles a week on it.

 

That's fairly standard of a setup for most any tranny out there these days. It sounds to me like you're due for a u-joint replacement on the rear drive shaft.

 

so the movement i found is normal where the yoke goes into the tranny? a little leakage is fine as well? can that seal be replaced when i pull the driveshaft? will i need a plug for the tranny when i pull the yoke?

 

There will be a little play, but it is hard to see exactly what you have. I never have replaced the tail shaft seal in an Expy but I am sure you can. Also on U joints, I had one once that every time I came to a stop the car would shake. Most of the time you would go for disks or front end parts which I replaced, but it ended up being the U-joints. The rear one was frozen solid. It came right out, put a new one in vibration gone. So just because the u-joint dosn't have slop in it doesn't mean it is good.

 

The driveshaft yoke must slide in and out of the transmission (or have a slip joint in the driveshaft) to allow for up and down motion of the axle. Movement other than that is bad.

Leaks are never normal. Yes you can replace the output shaft seal on the trans.

Replace the u-joints
Replace the trans seal

 

well, i replaced the u joints tonight. i couldn't get a seal till friday. with the driveshaft off, the output shaft from the tranny moves about 1/4" total in all directions. there is much less shake now, but still some. i've had the tires balanced and inspected, u joints replaced, pinion bearing is good, axle bearings/shafts have no side play. what else could be causing this vibration from the back? rotors? output shaft? shocks bad? tires are getting close to needing replacement, but i'd rather not if i can hold off for now. i guess i should rotate the tires front to back once so see if that changes anything.

 

Sounds like replacing the u-joints got you most of the way to solving the problem. Since you still have some vibration then obviously there were multiple problems causing it. Rotating the tires to the front is a good idea because it will eliminate or confirm them as the cause for the rest of the vibration.

 

It could also be the drive shaft is out of balance. ????

 

well, the shake came back. could this be axle bearings? they aren't making any noise or leaking oil, but maybe? driveshaft was checked for balance and was ok.

 

It can be just a lot of things. That is problem. It sounds like you have hit the major ones. Have you rotated the wheels yet.

 

well, i had the wheels rechecked at another tire shop bechause things just didn't seem to be adding up. they checked them out with the road force machine and found that one was fine, one had 2# of force (not even noticeable), one had 24# of force, and the other a whopping 36#. i'm getting the 2 bad ones replaced tomorrow night. i'm not sure that this is the entire problem, but those two are deffinately bad and need to be replaced. this guy said that even though the tires wore fine and were balanced properly that sometimes they still will have road force issues. i hope this takes care of things.

 

Was curious if this fixed your vibration? I have an uncle with an expedition that is having a vibration issue and his ujoints seem fine too.

 

i replaced the rear tires, things got better but all gone. it's like i'm chasing my tail. the vibration now seems to be coming from the front left corner.

 

Thanks for the response. Glad it helped but sorry its not gone. Never even heard of Road force balance till i looked at this expedition forum. Wonder why these beasts are so picky about the tire balance.

 

it's not just expeditions, most any large tire has more problems with road force.