Topic: viberation coming from my buddys truck?

[Halladay]

so his truck drives smooth untill he gets up around 45 mph then the truck starts viberating when he lets off the gass it goes away we got no idea whats going on anything would help thanks. its an 86 extcab 22re

[79coyotefrg]

sounds like a bad ujoint   or it could be the drive shaft is not in phase

[Halladay [OP]]

sounds like a bad ujoint   or it could be the drive shaft is not in phase

thats what i was thinkin but he said he coludnt tell if it was coming frome the front or rear...

[79coyotefrg]

tell him to unlock his hubs, he's not supposed to leave them locked on the highway

[Snowtoy]

Where are the vibrations being felt, i.e., through the seats, the steering wheel, etc.?  The area the vibrations are coming from will help us help you to locate the problem.

Steering wheel vibrations usually means the tires i.e., balance, separation, out of round
Vibrations through the seats usually means pinion angles or u-joint wear.

Does the vibrations continue above 45mph, or do they go away?

[axled89]

good call on the unlocked hubs. 

[Halladay [OP]]

alright hubs are unlocked and thats not the problem haha..  they were never locked.. the vibration starts at like 45 and goes away at 55 and you feel the whole freaking truck shake. but its not in the steering wheel... its nothing the the death wobble i have had..

[83 Crawler]

my truck did that too i replaced my ujoints and it went away...

[79coyotefrg]

u joints or drive shaft is not in phase

look at the yokes on this driveshaft, 

[79coyotefrg]

[79coyotefrg]

 

We say that 2 u-joints are in-phase if they are fitted to yokes that are fixed on the same shaft, such that the 2 opposing bearing caps in the u-joint that are held captive by the yoke on the shaft (the inboard yoke's u-joint caps) are both in the same orientation.
   

A pic is worth a thousand words. Look at the pic to the left. In the top shaft, the 2 joints indicated by the green arrows (ignore the fact that the right-most is part of a double cardan CV assembly) are in-phase because in both joints, the bearing caps held captive in the shaft are both vertical, while the bearing caps that are free (not held captive in the shaft) are both horizontal. If you then look at the bottom shaft, you will notice that this is not the case with the joints indicated by the blue arrows. The left has captive bearing caps vertically oriented, while the right most joint has it's captive bearing caps oriented horizontally. The joints are therefore 90° out of phase.

 

[1985SR5]

I had the same issue, vibrating like crazy at 45 mph. Thought is was a u-joint, turns out that the bolts that hold my driveshaft to the rearend had came loose. Tightened them up and have had no problems sense.

[MR.FULL-FORCE]

Mine was vibrating like that to.But around 50-85 mph.I changed my throwout and pilot bearing and it went away...