Vibration no one can find

Have you checked to make sure that the powerdivider is not jammed up in the locked position , if the tires are a bit different diameter and it is locked the torque windup to the point of slipp could cause the symptoms you describe

 

As he said, Also check the ratios, I have seen a truck built out of the factory with 3.70 front diff and a 3.55 rear. Turck had a vibration not found for 140 000 kms before the power divider failed. Peterbilt replaced the power divider due to twice before finding the rear diff ratio wrong.

 

i didnt think about that,good suggestion.

 

That is a very good suggestion, when I was in Alberta we had a bunch of trucks that had the rear axle diff lock that was assembled wrong and when it was engaged on the dash it was actually out, we did not find it until we put it on stands and the rear axle was found to be locked. The tire man had complained of the new trucks eating drive tires especially the rears. That should not be a problem on the dyno. Having the wrong ratio's is not that uncommon. Ford threatened to sue us once for telling a customer. That would give you a better chance of a shudder. The dyno we had used 4 rollers and if you put in the locks it read out speeds on each axle. Just a thought!

 

Driveshaft balanced? If the drive was stressed past modulus of elasticity it would be out of "balance" think licorice stick. It may have only been destructed to the point of errant vibration but not to the point of visual evidence on your pre-trips. Just a thought. it is probably cheaper than wheels and drums

 

Your dealing with too many variables here yet. I have seen Cat dealers approach this a little differently. 1st they sling the engine itself ( off the motor mounts) and then run it with a Vibration meeter hooked up. Vibrations can be read as 1st order vibration, 2nd order vibration etc. which will identify the order of the vibration harmonics to certain components such as a crankshaft, or an electrical component which all give off different orders. Can't remember exactly but a 1st order might be the same vibration the engine produces at a certain Rpm, other orders of vibration might be a component that produces a half order which may suggest a cam etc.
Stewart and Stevenson should have access to a similar engineering tool. You need to get a technical advisor at the dealership involved. Keep going higher in the organization until you hook up with the right manager or call Detroit diesel's help line.
Not a cheap soultion and very labor intensive but, until you isolate and identify the root cause, it will drive you and your pocketbook nuts!
Good Luck.

 

Was you're problem solved?