Okay here we go. I Replaced the U-Joints in my 88 iroc, and then a vibration started in at 65mph and above, what could it be? I have a poly tranny mount, but was on before u-joint swap and acted fine. What will cause the vibration AFTER new u-joints?

 

One of 2 things: either you have a roller stuck between the end of the trunnion and the cap, or you bent an ear of the yoke.

 

I did mine once and had the same issue; the driveline shoppe where I bought parts re-did it and it was then fine. And neither of the above 2 things occurred. Don't feel bad is all I'm saying. LOL

 

May not be seated "just right" had the same issue with mine. Looked to be right but wasnt. Get rid of the poly trans mount and get a rubber one in there.
Has to be some give in the drivetrain will also cut down on vibration.

Lotsa guys break trannies/cases from too rigid a trans mount.

 

I tried a rubber mount again, tranny rips it apart after a couple hours, lol has a gnarly shift kit. N thanks for the reply guys, I guess I'll take the shaft back out and look it over carefully! Can't really have it in the shop, my daily driver n too cold to ride my motorcycle. Fml!

 

get the shaft out and rock the rear joint lock to lock. if you feel ANY hangs, bumps or resistance this will cause the runout your feeling. take the caps off the open end and tap the neck of the driveshaft as this will walk the caps and let them seat. do this to he yoke end as well.

another thing to look at is the C clips that were supplied. if they were too thick and were waay hard to pop into the slots you may need to shave a bit off so they seat comfortably.

i have had shops in town do joints in my driveshafts and had only a time or 2 that they came out right. talked to a guy from Driveline at a NMCA event in the midway and he gave me ips and tricks to why i was having the issues i was having and i have never had another shop replace my joints since. they have balanced my shafts but never joins.

my car has been silk ever since.

 

Try rotating the shaft 180* in the yoke.

 

another thing to remember, the factory aluminum driveshafts have different u joints then the steel ones.. make sure you get the right one. once i put the wrong type in there and not even 30 miles the u joint was shaking like crazy and eventually busted....

 

good point


also, to the OP; you didn't lose the weight which was probably on the driveshaft did you?

 

NAPA U joints for JG1 RPO alum drive shaft - third gen 372(R) 369(F)

 

I agree. Take out the driveshaft, and re-install it 180 degrees from where you had it originally. Sometimes that rids of the issue. Silly question too.....you did grease them right? lol

 

If youre ripping a trans mount out after a few miles may wanna check your motor mounts sometihing is wrong

 

i had this problem after a local shop changed my rear u-joint.they didnt have the clips in right and it vibrated than finally after about ten miles came out of the rear yoke almost completly.the u joint got caught in yoke i was verry lucky

 

As you can see, alot of "check your work" kind of stuff...