TM  10-3930-643–34 INTRODUCTION. Section  II. EQUIPMENT  DESCRIPTION  AND  DATA 1-8. Differences in Models. Read  Operator’s  Manual (TM  10-3930-643-10) paragraph 1-9 and Organizational Maintenance Manual (TM 10-3930-643-20) paragraph 1-8 for differences in models. In addition, note the following differences  as  they  affect  maintenance  tasks. a. Front Axle Assembly. (1) S/N 2000 and below. Three piece axle assembly. (2) S/N 2001 and above. One piece axle assembly. b. Rear Axle Assembly. (1) S/N 2000 and below. Three piece axle assembly. (2) S/N 2001 and above. One piece axle assembly. c. Power Cluster/Pressure Converter and Reservoir. Nomenclature difference. Power cluster is on S/N 2000 and below and pressure converter is on S/N 2001 and above. d. Two-Way  Valves/Check  Valves-Treadle. Nomenclature  difference. Two-way valves are on S/N 2000 and below and check valves are on S/N 2001 and above. e.  Treadle  Valve. Internal  design  difference. f. Ground Driven Steering Pump. Internal  design  differences. g. ROPS/Cab. (1) S/N 2000 and below. Equipped with ROPS. (2) S/N 2001 and above. Equipped with cab. h. Heater Assembly. (1) S/N 2000 and below. NO heater assembly. (2) S/N 2001 and above. Equipped  with  heater  assembly. 1-5/(1-6  blank)