Get under the truck with the rear wheels raised and turn the driveshaft by hand and see if there is slop or slack in the U joint before the axle begins turning. Even a few thousandths of an inch of play can give you a vibration.

Try to move the shaft from side to side and see if the is any play at the U joint / yoke.


1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)