Step-by-Step Rear Shock Oil Change for DHX2 Trunnion

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The Fox DHX2 Trunnion [paid link] rear shock is a high-performance component designed to deliver exceptional ride quality and control for aggressive riders. As part of regular maintenance, an oil change is essential for ensuring the shock operates smoothly and efficiently. Over time, the internal oil can break down or accumulate contaminants, which can degrade performance. In this guide, we’ll walk you through the process of performing a rear shock oil change for the Fox DHX2 Trunnion [paid link], ensuring that your shock remains in top condition.

Tools Required

  • 8mm hex wrench
  • 10mm socket wrench
  • Shock oil (Fox Float Fluid or equivalent)
  • Shock pump
  • 2.5mm, 3mm, and 5mm hex wrenches
  • Torque wrench [paid link]
  • A clean towel or rag
  • Plastic or rubber gloves
  • Small parts tray for organizing components
  • Fox DHX2 specific service kit (O-rings, seals, and gaskets)
  • 1.5mm snap-ring pliers (optional)

Disassembling the DHX2 Trunnion

1. Remove the Shock from the Bike

  • Begin by carefully removing the rear shock from the bike frame. Depending on your setup, this may involve removing the bolts at the shock mounts using a 5mm or 6mm hex wrench.
  • Use a towel to protect the shock and the frame during the process. Be mindful of any cable routing or additional components that may interfere with the removal.

2. Remove the Air Can

  • Use an 8mm hex wrench to unscrew the air can from the shock body.
  • Place the shock on a flat surface and slowly twist the air can off. Be gentle, as overtightening can damage seals or other components.

3. Drain the Oil

  • Once the air can is removed, you’ll need to drain the old oil. Position the shock with the damper side facing down to ensure all oil flows out.
  • Let the shock sit for a few minutes to ensure maximum oil drainage. You may use a clean rag to wipe away any excess oil on the shock body.

Inspecting Internal Components

4. Remove the Damper Cartridge

  • To access the internal components, you must remove the damper cartridge. This involves loosening the 10mm bolt that secures the damper to the shock body.
  • Carefully pull out the damper cartridge, ensuring you do not damage any internal seals. Inspect the cartridge for any signs of wear or damage, especially around the seals.

5. Remove the Internal Parts

  • Use the appropriate hex wrenches (typically 2.5mm, 3mm, and 5mm) to remove any internal parts, such as the shock seals and piston.
  • Be methodical and organized in removing each component. It’s recommended to lay them out in order to help with reassembly.

Cleaning and Reassembling the Shock

6. Clean All Components

  • Thoroughly clean all components of the shock, including the damper cartridge, seals, piston, and any other internal parts.
  • Use a rag or towel to remove old oil and dirt. Avoid using harsh cleaning solvents that could damage the components.

7. Install New Seals and O-Rings

  • Replace any worn or damaged seals and O-rings. Use the Fox DHX2-specific service kit to ensure you have the correct parts.
  • Lubricate the new seals with fresh shock oil before installing them to avoid friction and ensure a proper seal during reassembly.

8. Reassemble the Damper Cartridge

  • Carefully reassemble the damper cartridge by following the reverse order of disassembly. Ensure that each internal part is positioned correctly and that the seals are seated properly to prevent leaks.
  • Torque the damper bolt to the manufacturer’s specifications (typically around 30-40 Nm). Double-check the tightness of all fasteners to avoid issues during riding.

Filling with Fresh Oil

9. Add Shock Oil

  • Using a syringe or small container, slowly add the recommended shock oil (Fox Float Fluid or equivalent) to the damper cartridge.
  • Add oil in small amounts to ensure even distribution and avoid air bubbles. The oil should reach the appropriate fill level as specified in the Fox DHX2 manual.

10. Compress and Cycle the Shock

  • With the oil added, slowly compress and extend the shock to allow the oil to fully distribute throughout the damper. This helps eliminate air bubbles and ensures smooth operation.
  • Keep cycling the shock until you feel consistent resistance during compression and rebound movements.

Reassembling the Air Can

11. Reattach the Air Can

  • Once the internal components are properly lubricated and assembled, carefully reattach the air can to the shock body.
  • Tighten the air can using an 8mm hex wrench, ensuring that it is securely fitted without overtightening, which could damage the seals.

12. Reinstall the Shock

  • With the shock fully reassembled, reinstall it onto the bike frame. Be sure to tighten the mounting bolts to the manufacturer’s recommended torque settings.
  • Use a torque wrench [paid link] to ensure proper tightening without damaging the shock or the frame.

Testing the Shock

13. Check for Leaks and Functionality

  • Before heading out for a ride, pressurize the shock using a shock pump to the recommended PSI.
  • Test the shock’s functionality by cycling through the compression and rebound adjustments. Check for any unusual noises or resistance.
  • Inspect the shock for oil leaks or signs of damage.

14. Perform Final Adjustments

  • Fine-tune the compression and rebound settings to your preferred riding style.
  • If you’re unsure of the proper settings, refer to the manufacturer’s guidelines or consult a bike technician to ensure optimal performance.

Troubleshooting Common Issues

1. Leaking Shock

  • Leaks typically occur from worn seals. If the shock continues to leak after the oil change, inspect the seals and O-rings for damage. Replace them if necessary.

2. Poor Rebound or Compression

  • If you notice sluggish or erratic performance in rebound or compression, it may be due to improper oil levels or air bubbles inside the damper. Recycle the shock to release any trapped air, or add oil if levels are low.

3. Noisy Shock

  • A noisy shock can result from insufficient lubrication or worn seals. Make sure that all parts were properly cleaned and lubricated during reassembly.

Conclusion

Performing an oil change on your Fox DHX2 Trunnion rear shock is essential for maintaining the shock’s performance and longevity. By following this step-by-step guide, you can ensure that your shock continues to deliver exceptional performance on every ride. Always use the correct tools, oil, and replacement parts to ensure proper assembly and avoid future issues. Regular maintenance will help you get the most out of your shock, keeping it responsive and reliable for all your trail adventures.