I have a 1999 International 4900. 5th and 6th gear truck shakes and can feel vibration in the shifter under load, when not under load feels smooth. As soon as I start to accelerate the shaking and vibration comes back?
Not necessarily in the trans. Vibrations travel. Honestly, could be anywhere from the tires forward. No good way to guess without inspecting
Start with a basic drive line inspection paying attention to u-joints, spinning caps and loose straps. Check your suspension and u-bolts to make sure you don't have an axle that is coming loose and pitching up excessively when torqued is applied.
What engine? On n14 it can be even an injector issue. But yeah, it can be tires, wheels, driveshaft, bearings, whatever
