926M, 930M and 938M Wheel Loaders Power Train Piston Motor (Hydrostatic) - Assemble - Rear Hydrostatic Piston Motor Caterpillar


Piston Motor (Hydrostatic) - Assemble - Rear Hydrostatic Piston Motor
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1.1. Assembly Procedure

Assembly Procedure

Table 1
Required Tools 
Tool  Part Number  Part Description  Qty 
6V-2055  Grease 


    Illustration 1g03876481

  1. Install and lubricate new rings with clean hydraulic oil.

    Note: Piston rings (65) are not symmetrical. Note proper Orientation (X).

    Note: Mark (Y) indicates top of piston ring.



    Illustration 2g03876443


    Illustration 3g03876586
    Seal Installation Tool

  2. Lubricate bearings and press shaft assembly (64) into motor housing (30).

  3. Lubricate and install new O-ring seal (66) on shaft locking screw (67). Install shaft locking screw (67). Tighten locking screw (67) to a torque of 8 N·m (70 lb in).

  4. Lubricate inside diameter of new lip seal (63). Cover the shaft splines with shaft cover or packing tape to avoid damaging lip seal (63) during installation.

  5. Using seal installation tool, press lip seal (63) into housing bore.


    Illustration 4g03876553

  6. Position the motor with shaft assembly pointing down.

  7. Using Tooling (A) to retain shaft rollers (59B), install shaft rollers (59B) on the journals of synchronizing shaft (59). The shaft rollers are symmetrical. You may install the shaft rollers in either direction on synchronizing shaft (59).

  8. Position each shaft roller (59B) with outside edge flush to the end of the synchronizing shaft journal.

  9. Install one synchronizing shaft support pin (59A) into the spring guide of the motor shaft.

  10. Install synchronizing shaft (59) and shaft rollers (59B) into the motor shaft.

  11. After installation, tip and rotate the synchronizing shaft in all directions to check for binding.

    Note: Ensure synchronizing shaft rollers move freely in the races of the motor shaft.



    Illustration 5g03876559

  12. Position the shaft assembly (64) as shown.

  13. Tip the three pistons closest to the minimum angle stop out, toward the housing.

  14. Tip the six remaining pistons forward toward the lowest part of the end cap mounting surface.

  15. Tip the synchronizing shaft forward (toward the lowest part of the endcap mounting surface).


    Illustration 6g03876560

  16. Using Tooling (A) to retain one of the synchronizing shaft support pins into the recess in cylinder block (60).

  17. Position cylinder block (60) so one of the synchronizing shaft roller raceways are aligned between the two bottom pistons.

  18. Install cylinder block (60) and the synchronizing shaft support pin on the lower six pistons and the synchronizing shaft.

    Note: The synchronizing shaft rollers enter their races in cylinder block (60), while the last two of the six pistons enter their corresponding bores in the cylinder block.

  19. Insert a brass rod through the cylinder block kidneys to guide the pistons into position.

  20. Start with the six pistons closest to the lowest part of the end cap mounting surface.

    Note: The synchronizing shaft support pin enters the recess in the synchronizing shaft.

  21. Lift cylinder block (60) slightly.

  22. Guide the remaining three pistons into their bores.

  23. After the last piston is in position, check the position of the rollers by trying to turn the cylinder block. It should not have any free travel. If a roller is not in position, remove block (60) and repeat steps 7 through 22.

  24. Maintain an inward force on cylinder block (60).

  25. Carefully push cylinder block (60) toward the highest part of the end cap mounting surface. Tilt the housing back so the cylinder block remains in place.

  26. Hold the cylinder block and turn the shaft in both directions. If you feel any play, one or more of the rollers are not in place.

    Note: Ensure synchronizing shaft rollers move freely in the races in the motor shaft. If installed correctly there is no free play between cylinder block and shaft.

  27. Lubricate the pistons and cylinder block bores liberally with clean hydraulic fluid.

  28. Hold cylinder block parallel to endcap surface of housing until the piston head is installed.

  29. Install bearing plate (61), with its steel side facing cylinder block (60).

  30. Lubricate the bronze side of bearing plate (61) with clean hydraulic oil.


    Illustration 7g03876562


    Illustration 8g03876561

  31. Lubricate and install servo piston (51).

  32. Lubricate and install setting lug (52).

  33. Install new pin (50) and set screw (49). Ensure pin (50) is in groove of setting lug (52). Tighten set screw (49) to a torque of 35 N·m (310 lb in).

  34. Lubricate and install valve segment (54). Ensure valve segment (54) spindle properly sets on the setting lug ball. Install hold down screw (55). Tighten hold down screw (55) to a torque of 6 N·m (53 lb in).

  35. Lubricate and install O-ring seal (57B) and seal ring (57A) onto servo piston head (56). Press onto servo piston (51). Take care not to damage seal group (57).

  36. Install bolt (36). Do not tighten until the endcap is installed.


    Illustration 9g03876582
    Typical example. The piston head may be oriented by 180 degrees.


    Illustration 10g03876583
    Bolt tightening sequence.

    ------ WARNING! ------

    Improper assembly of parts that are spring loaded can cause bodily injury.

    To prevent possible injury, follow the established assembly procedure and wear protective equipment.


  37. Install locator pins (58) in motor housing (27).

  38. Install new gasket (53).

  39. Install piston head (34) in position marked during disassembly.

  40. Install bolts (35).

  41. Tighten bolts (35) by hand using sequence shown in Illustration 10.

  42. When end cap is properly seated, tighten bolts (34) using the sequence shown in Illustration 10 to a torque of 210 ± 10 N·m (155 ± 7 lb ft).

  43. Rotate the motor shaft and check for play between the shaft and cylinder block. Any play indicates that the synchronizing shaft rollers are not installed correctly.


    Illustration 11g03876584
    Typical example. The piston head may be oriented by 180 degrees.

    ------ WARNING! ------

    Improper assembly of parts that are spring loaded can cause bodily injury.

    To prevent possible injury, follow the established assembly procedure and wear protective equipment.


  44. Lubricate and install spool (43), springs (42), and (44).

  45. Lubricate and install new O-ring seals (45) onto plugs (40) and (46).

  46. Install plugs (40) and (46). Tighten plugs (40) and (46) to a torque of 67 ± 3 N·m (50 ± 2 lb ft).

  47. Lubricate and install new O-ring seal (47) onto loop flushing valve (48).

  48. Install loop flushing valve (48).

  49. Install retaining ring (62) into the housing bore.

  50. Use seal installation tool to press lip seal (63) and retaining ring (62) into the housing until the retaining ring snaps into groove.


    Illustration 12g06043407

  51. Tighten previously installed bolt (36) to a torque of 210 ± 10 N·m (155 ± 7 lb ft).

  52. Lubricate and install new O-ring seal (39) on speed sensor (37).

  53. Install speed sensor (37) and bolt (38) into motor housing (27). Tighten bolt (38) to a torque of 8 N·m (70 lb in).


    Illustration 13g06043408


    Illustration 14g06043368

  54. Install cover (32), new O-ring seal (33), and bolts (31). Tighten bolts (31) to a torque of 110 ± 5 N·m (80 ± 3 lb ft).


    Illustration 15g03876211

  55. Install displacement limiter (28) and new nut (29) to original position.

  56. When motor is properly adjusted torque nut (29) to a torque of 45 ± 2 N·m (33 ± 1 lb ft) and install cap (30).


    Illustration 16g03876163

  57. Install shuttle valve (18) into side of control housing (2).

  58. Lubricate and install new O-ring seal (17) onto plug (16). Install plug (16) and tighten to a torque to 40 ± 2 N·m (30 ± 1 lb ft).

  59. Install orifice (21) and orifice (24) to both sides of control housing (2).

    Note: Orifice (21) and orifice (24) are not interchangeable.

  60. Lubricate and install O-ring seals (20) and (25) onto plugs (19) and (26). Tighten plugs (19) and (26) to a torque of 8 ± 1 N·m (70 ± 8 lb in).

  61. Lubricate and install spool (15).

  62. Install new O-ring seal (14), and solenoid (13), and bolts (12) onto control housing (2). Tighten bolts (12) to a torque of 6 ± 1 N·m (53 ± 8 lb in).

  63. Install O-ring seal (11), coil assembly (10), O-ring seal (9), and nut (8). Tighten nut (8) to a torque of 3.5 N·m (31 lb in).

  64. Install O-ring seal (7) and cap (6).


    Illustration 17g06043362


    Illustration 18g06043361

    ------ WARNING! ------

    Improper assembly of parts that are spring loaded can cause bodily injury.

    To prevent possible injury, follow the established assembly procedure and wear protective equipment.


  65. Install gasket (5), spring (3), spring guide (4) control housing (2), and bolts (1). Tighten bolts (1) to a torque of 37 ± 2 N·m (27 ± 1 lb ft).

End By:

  1. Install the hydrostatic piston motor.

Information System:

926M, 930M and 938M Wheel Loaders Power Train Piston Motor (Hydrostatic) - Disassemble - Rear Hydrostatic Piston Motor
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