I've got an '83 pickup that I've replaced the in three months ago. I noticed two days ago a strong vibration in the seat when going over 65 mph. If I press in the clutch the vibration goes away. If I release the clutch whether in gear or neutral the vibration returns but goes away under 65 mph. My fix is to not go over 65 mph but I'd like to know what I could have done wrong with the clutch install. It works flawlessly. All I can figure is something on the pressure plate.

Thoughts?

 

mine was doing that exact thing (vibration under power, not when the clutch was in or coasting in neutral) turned out to be a bad u joint in the driveshaft. Slide under the truck and turn the driveshaft by hand and see if there is any slop.

 

Here's a link to my previous thread with some other ideas:

https://www.yotatech.com/forums/show...ibration+power

 

I'll check that for sure. Someone else mentioned that as a possibility, too.

 

I removed the driveshaft and there is slop in both the rear end and transmission but I can see any movement in the ujoints. The flange on the rear end will move 1/4" or so. I jacked up the rear end and turned the flange moving the wheels. It feels slightly rough but nothing I wouldn't expect from a 23 year old vehicle.

 

Is the driveshaft itself true? I had a problem like this and it turned out the shaft was bent ever so slightly.

 

Do you leak from either the transfer case output or the diff? How are the fluid levels in both?

Sounds like it's time for an output seal/bushing and a new crush sleeve for the pinion...

 

Replace your u-joints first. That's generally the problem. If that doesn't fix it, I would take your driveshafts to a machine shop and have them balanced. An unbalanced driveshaft, more often than not, is almost impossible to see by eyeballing it up.

 

It's leaking only at the pinion at the flange and I only found it when I removed the drive shaft.

Will an out of balance drive shaft start a major vibration all of a sudden or wouldn't it be a slow onset of vibration?

The u-joints seem rock solid and I feel nothing out of the ordinary when I move them in all directions. When I removed the flange the post that it bolts to was very, very loose and I could feel the gears moving around inside.

I've been searching the forum for threads on diagnosing a bad third member. Can anyone point me in a direction there?

 

PM Zuk for all things gears/thirdmembers

 

The driveshaft u-joints will wear out sooner. Sometimes they will only last 1500 miles. If you have low gears, the shaft spins faster, and the joints will wear out even quicker.