Ok so this is where I'm at. The speedo works when the back tires move. Either from being towed or from engine power. Must have a broken shaft because rpm seems faster than the tire is turning when one tire is jacked off the ground. Must not be a posi rear end but is a torque tube. All original truck. as far as i can tell. Since the speedo moves only when the tires turn my break must be before the speedo.
