O.K., Guys with the 60 to 66 at least C-10's with the swing arm rearends.....Go check your U-bolts that hold the rearend to the swing arm. Ours were rusted over half way through. Replaced them with POL (performance on line.com) bolts. The rear end upper U-bolt cup acts as a rain catcher & rust will occur. Ours did ---big time.