Power Train Vibration

I have owned a 2007 GMC Sierra Classic, w/Duramax/Allison combo, 4WD, Crew Cab, Long Bed, for nearly 2 years. While towing my 5th wheel there is a vibration in the power train--most noticeable between 55-65 MPH. For nearly 2 years, the local dealer has been attempting to locate the problem, but has been unable to do so. Attempts to correct the problem have ranged from installing pinion angle shims, new driveshaft, etc. The combined GVWR for the truck and 5th wheel is 17,960 lbs, which is well below the rating for the truck. Has anyone with a comparable truck experienced a similar problem?
:confused:

Has the truck always had this issue??


Has the phase on the U J Joints been checked.

If the joints are not looking at one another exactly they will vibrate like crazy.

This can happen if a shaft was not built correctly or if someone got hard with it and actually tweeked the shaft.

The only way to be sure is to remove the drive shaft and and the joints and insert a shaft through the u joint bores and then indicate them to be
sure both bores are in the same plane.

If the joints are off as little as a couple degrees will be all it takes to shake things

If the truck has a two piece setup be sure that all the joints are running with each other.

U joints speed up and slow down 4 times per revolution. If they are not phased correctly one will be slowing while the other is trying to speed up and things get real hinky.

Run the rig With the rear wheels off the ground make sure the drive line is not wobbling. If it wobbles there is an issue

Give this a go and let us know.

Robyn

My 08 has the same problem. My 03 didn't! Differences, 1) 08 is a Crew Cab, and 2) the 08 has a 2 piece drive shaft. I believe this is the major source of the problem is the 2-piece drive shaft. I only notice the vibration when I have the 5ver connected or I have the ATV in the bed,

I have to take the truck in for the Heated Winshield Washer recall so I am going to ask if a one piece drive shaft is available for a crew cab.

Driveline angles are critical in a two piece unit.

All the joints have to have complimentary angles. This means that the joint at the differential has to be the same as the joint at the carrier (Center bearing) and the tranny. If the angle of one of these is off then the setup will vibrate.

A u joint speeds up and slows down 4 times per revolution and when one end of the shaft is doing its thing the other end has to be doing it too.

If there is an angle issue or a phase issue things dont work right and therein lies the cause of most "Bad Vibes"

You can check the angle with a little magnetic protractor.
These have a mag base and a dial. The mag base can be stuck to the flat on any joint and the angle read.

Allowable variation is 1/2 degree. 1 degree off will usually be ok.

With the issue showing up when you weight the truck down pretty well points to an angle issue.

Differential pinion angle may be off some from nominal and when you weight the truck it falls to far from where it should be.

There are tapered shims to adjust this (Go between spring and the perch)
Sometimes a shim between the carrier and the mount can help.

Good luck

Robyn