WHILE ASSISTING TO REMOVE THE REAR DRIVELINE ON TRW335 RIMPULL COAL HAULER, EE PLACED HIS RIGHT HAND ON THE U-BOLT THAT SURROUNDS THE DRIVELINE. THE DRIVELINE DROPPED APPROXIMATELY 8-9 INCHES ONTO THE U-BOLT PINNING EE'S FIFTH RIGHT FINGER AGAINST THE THE U-BOLT. A CONTRACTOR EE WAS ASSISTING EE WHEN THIS OCCURRED. A LACK OF COMMUNICATION BETWEEN THE TWO EMPLOYEES CONTRIBUTED.