troubleshooting a bad vibration?


I know my front driveshaft vibrates when im in 4wd and do over thirty but with my hubs unlocked and in 2wd i get a bad vibration all over when i go over 40mph and sometimes when im going slower, you can feel it in the steering wheel and the transfercase shackes, I check the t case and its well secured cant move it with a prybar and the motor mounts and trans. mount all look strong,I dont think its the rear driveshaft you can grab it and it dont give like my front one,now i had 4.57 put in the diffs like a month ago, could there be sumtin with that?

any suggestion would be help,thx

maybe the 2 peices of your drive shaft are'nt alined.
   there are two punch marks on each peice,1 one the end of the splined and 1 on the yoke peice aline them.
       oscar

That's normal for Jeeps  

OK, I just read the mice type on
the bottom of your posts, now I
know what you are driving  

Front driveshaft is location oriented
on a Sidekick, 180* out caused a bad
vibe on mine.

I'd check for driveshafts being out of
phase, or out of straight

i was yapping with a mechanic at the zuki dealership the other day, asked the same ?. he said he had one in for the same thing. went through everything( u joints felt good), after removal and inspection all the u joints had hairline cracks, changed them all and drove smooth as new.