Truck developed a nasty driveline vibration at about 2000 RPM going down the freeway, causing the dashboard in particular to rattle and resonate.
Stabbing the accelerator up to 2500 RPM or simply lifting the pedal, would bring the truck out of resonance with an audible metallic clanking as the driveline unloads.
These are symptoms of a worn ujoint in the rear driveshaft (connecting the 10.25″ Sterling rear axle pinion yoke).
The ujoint hasn’t completely sheared apart. The cups first wear into the ujoint cross shaft causing the needle bearings to fall out and for the cross shaft to be wedged off-center in the yoke under the ujoint straps.
Single rear wheel 4×4, double cardon front and single ujoint rear driveshaft, regular cab long bed.
Found a replacement in stock at a local parts store and changed the ujoint in their parking lot.
Napa p/n UJ331
Torx T-45 bit to remove the 4x driveshaft strap bolts,
Pliers to squeeze and remove the inner retaining clips,
Large socket as a drift and
Hammer to extract and reinstall the ujoint caps.
Mark relationship between balanced driveshaft and pinion yoke, to reinstall in the same orientation.
Apply penetrating oil to the ujoint caps at the yoke ears
The ujoint only has internal retaining clips outboard of the caps. Remove with pliers, and knock out the caps with the large socket and hammer.
Knock out one ujoint cup at a time, in the same direction. The ujoint comes out between the yoke ears.
Install new cups one at a time, using ujoint cross shafts to hold needle bearings in place.
Strike hammer against socket only, do not hit the new ujoint cap directly with a metal hammer.
Insert new retaining clips and ensure ujoint pivots smoothly.
(Smack driveshaft yoke ears with the hammer if ujoint is tight and binds.)
Reattach balanced driveshaft in marked positive relative to rear axle yoke.
Retorque bolts after test drive and wear in.