The 3/4 and 1 ton trucks use a full floating rear axle, which requires the axle shaft and bearings to be removed to allow removal of the brake drum/hub assembly. You will need a special socket to remove the lock/adjuster nuts from the spindle, its readily available from most parts stores. Here's a
manual page that shows how it comes apart. The page shown is for a '55, but the '66 will be essentially the same.
