Hey fellas, I've been working this 60mph vibration since last summer. Here's the deal. All's fine till I approach 60mph. Between 58 and 61 the old truck starts carrying on like a real bad tire bouncing. Kinda feels like the drive train is bouncing. Does it at that speed in any gear, neutral, RPM, any surface or grade. Otherwise this truck is tighter than new.
Here's what I've been thru: shocks/struts (new), 2 sets of tires (new/2 shops - no abnormal wear), wheels (20inch) spin true (2 shops), drive shaft balanced, rear diff opened/checked, rear axle (normal play, dealership), front ball joints and hubs checked (2 shops), cv axles and stubs (new/replaced), transmission shop says no problems.
It's almost teeth chattering and I'm out of ideas.
Transmission shop say all perfect, but
torque converter, possibly?
front drive shaft?

 

harmonic balancer ..? but only if RPM in neutral can make change... seen this..

missing balancer on half shaft...if original.

missing weight or damage to a brake rotor...

wheels/tires.. was the balance.. done with a spin balancer?

missing or damage to leaf spring eye bushings...

Take truck to real truck service garage... not car/dealer.... you know big straight trucks and semi- spring shop...

 

thanks chuck!
wheels/tires spin/"road pressure" balanced.
thought about harmonics, but I shut the motor off and coast. still same
new half shafts. found excessive play at the axle/stub connectors.
rotors/pads - spin quiet and same temp/heat on all corners.
Bushings - will check again, but no slop or audible over bumps detectable.

I may do the big truck shop. I'm a line haul driver, myself.
Thinking about a dyno/chassis test. Where a guy could walk around the truck while it's running, etc..