How to Repalce the Drive Hub Assembly on Stairmaster 4000PT


Learn about how to replace the drive hub assembly on a Stairmaster 4000PT stepper.


  • Snap Ring Pliers
  • Goggles
  • Socket Set
  • Wrench Set


  1. Remove the side covers.
  2. Remove the step chain retainers.
  3. Support the pedal arm.
  4. Unhook the pedal arm return spring from the spring hanger.
  5. Lift the step chain up and off the clutch sprocket and lower the pedal arm to the floor.
    1. Repeat on the other side.
  6. Remove the snap ring from the left end of the drive shaft. CAUTION: To reduce the risk of eye injury, wear eye protection when removing snap rings.
  7. Remove the drive chain.
  8. Remove the sprocket and other small parts from the left side of the hub assembly.
  9. Slide the drive shaft to the right, out of the hub assembly. CAUTION: If you remove the right-hand clutch sprocket from the drive shaft, do not confuse it with the left-hand clutch sprocket.
  10. Loosen and remove the two remaining bolts and nuts that hold the hub assembly to the frame.
  11. Remove the hub assembly.
  12. Inspect the drive shaft, bushings, thrust washers, and clutch sprockets for excessive wear or pitting.
    1. Replace any worn components.
  13. To reinstall the hub assembly, carefully reverse the disassembly procedures. Be sure that the right-hand and left-hand clutch sprockets are positioned correctly; the wide shoulder of the sprocket should be facing away from the hub on both sides.
  14. Chain Tension -
    1. The drive shaft is mounted in an eccentric hub. Rotate the hub so the marked hole is in the 12 o'clock position, lining up four holes in the hub with the four holes in the frame.
      1. Use this hub position when reinstalling the drive chain since the distance between the drive and the transmission shafts is at a minimum.
    2. The hub is in the proper position when the drive chain has a total of 1" to 1-1/2" of play, up and down, at the slackest point in the chain.
      1. If it is necessary to increase the tension or tighten the chain, rotate the hub counterclockwise until the chain has proper tension.
  15. Reinstall the covers.

You now have completed the replacement of the drive hub assembly on the Stairmaster 4000PT.

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