I have an '88 4x2 that vibrates at 55 miles per hour. It does not always vibrate, but when it does, it can shake quite hard. It has the frequency of an egg-shaped tire, but my tires are new and it shook with both the old and new. It has also had a recent alignment and lots of the steering parts are new.

I was thinking that it was possibly a U-joint, but they do not appear to have any play in them. Would a U-joint create a shake or would it be a higher frequency vibration?

Another thing I noticed when I was checking the U-joints is that I could easily push the transmission up about a half an inch or so. Is that normal or should the transmission mount should be firmer than that? Would a bad transmission mount cause the shake?

It also seems that the gear shift bobs up and down a lot, especially in 3rd and 4th gear (it is a 4 speed). Any other suggestions on what to inspect?

 

it sounds like a u joint problem, mine were dried up but not loose, i replaced them and the truck was alot smoother. my vibration wasnt quite as harsh as yours though. is your steering damper in good condition?

 

I think you could be on the right track, tomorrow is my day off so im going to do a twice over to track down my vibe's i actually thought about the tranny mounts.


also, my u's are brand new, driveshaft balanced, and brannnndd, i mean BRAND new tires.

 

Thanks for the replies. I looks like I should just change the U joints and see what happens since they are cheap enough. I figure after 263k they are probably getting a little dry.