Rear vibration

Sounds like tires but I'd check the U-joint. You didn't forget to grease it did you? I've seen this happen before.

Or just stay under 74mph...

 

your air ride may need adjusting.may be why u had to replacethe u joint.just an idea.

 

also the yokes can be bad

 

If they took the drive shaft out to replace the u-joint, make sure it got properly phased when reassemble.

 

Check carrier bearing too while you're checking all things above. I had one with a little slackin it. It mostly vibrated at high speed when transitioning from the motor holding the truck back to pulling. As you mashed on throtle slowly, it vibrated a little just as the motor went from hold back to pulling. Scared me as I had just rolled in new bottom end engine bearings, thought they had done something wrong.

Dave

 

Bad or flat spotted tires on the trailer can also cause a vibration in the tractor. I'm currently pulling one with a Flintstone tire on it that's causing my truck to shake like a million mile beater... likewise, no vibration bobtailing.

Do you pull the same trailer all the time?

 

I'm glad I read this thread. Because I'm having the same problem at 45 mph. Had the alignment checked. it was ok. But seeing s couple of spots on the tires. But it doesn't do it when I'm bob-tailing.

It looks like one of my king pins is getting lose...