Rough ride 2012 cascadia

Drive shaft balance, or the wheels need balanced. There is an auto level air valve on the drive axle air bags that automatically adjusts to keep the 5th wheel at a certain height. If it's neutral position is set too high or too low, the drive shaft will be spinning off of its neutral axis and send the shakes through everything. There are places that repair drive shafts, I bet they could look at it and know. If the drive shaft is fine then it would be just getting the air valve adjusted back to zero.

 

Sell it.

If it shakes everything in the cab the way I imagine it and 6 years old. Dump it.

 

I would just add to check your wheel bearing adjustments and check your cab mounts and cab suspension. It could possibly be the cab itself throwing you around.

 

Mine did that.
Driveline angles are not right from the factory.
I added 3/8” to the length of the rod to the levelling valve. Worked for me.
Video FreightShaker

 

Start with your tires, which should be balanced when the shocks are put on.

 

With aircraft, if you have a vibration (usually in a heli) you ask the pilot of it's a rapid vibration or a buzzing type vibration. Rapid would mean the main rotor, buzzing would be the tail rotor as it spins so fast any vibration caused by it would be felt as a "buzz" by the pilot.

So is the vibration at about the same rate that the tire turns or the same rate that the driveshaft does? This would tell you what's causing it. Also if the vibration speed changes rapidly with throttle it's caused by the engine.