I drive a freightliner Columbia daycab with a 13 spd. There is vibraton when under power in high gears, usually when climbing smaller hills and around 1200-1400 RPM. It is not bad but enough to rattle stuff in the cab, and stops immediately when I back out of it and/or coast. Any ideas?

Steve

Check all your driveshaft yokes where they attach to the splines on the trans & rears. A loose yoke can cause a torque sensitive vibration such as you describe. Also check for looseness in the driveshaft slip joints. If any of these parts are loose, fix it immediately. The vibration can eventually damage other parts, and a driveshaft coming apart at highway speed is not pretty.

If your truck is on air ride check the ride height. Improper ride height messes up the driveline angles and can cause vibration (and driveline damage).

Another possible cause would be a defective harmonic balancer at the front of the engine crankshaft, however that should cause a vibration when pulling in any gear, not just in the high gears. Running an engine with a defective harmonic balancer can lead to a broken crankshaft.

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