Keeping Your 40 Factory Suspension Fork in Top Shape at Home

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The Fox 40 Factory suspension fork is a high-performance component built for aggressive downhill and freeride mountain biking. Known for its stiffness, adjustability, and smooth damping performance, the 40 Factory requires meticulous attention to detail to maintain its peak performance. This guide provides technical insights into installation, adjustment, and routine service, along with tips for troubleshooting and compatibility checks—all tailored specifically for the Fox 40 Factory model.

Tools Required

  • Torque wrench [paid link] (4–20 Nm range)
  • 32 mm cassette tool or crown race setter
  • Suspension pump
  • Allen key set (1.5 mm to 8 mm)
  • Shock oil (Fox 20wt Gold and Float Fluid)
  • Clean cloth and isopropyl alcohol
  • Seal driver (for 40 mm stanchions)
  • Pick tool or seal hook
  • Fox damper bleed kit [paid link] (if servicing the damper)

Installing the Fox 40 Factory Suspension Fork

Proper installation is vital to avoid performance loss or component damage. Start by inspecting the steerer tube length and trimming it if necessary using a pipe cutter. Install the crown race securely using a race setter tool. Ensure headset bearings and cups are properly greased before inserting the fork.

Mount the fork through the headtube and secure the top cap and stem bolts using a torque wrench [paid link] to Fox’s specified values. Finally, install the brake caliper using the appropriate adapter for your rotor size, ensuring alignment and no rotor rub.

Initial Setup and Adjustment

Before hitting the trail, dial in the fork’s air spring and damping settings to match rider weight and style. Begin with the air spring:

  • Set the air pressure using Fox’s rider weight chart as a baseline.
  • Adjust compression and rebound damping via the top crown dials.
  • The high-speed compression adjusts for big hits and landings.
  • The low-speed compression fine-tunes fork behavior under braking and cornering.
  • Rebound settings control how fast the fork returns after compression.

Use small incremental adjustments during test rides to hone in the ideal setup.

Routine Maintenance and Service Intervals

To extend the life of the 40 Factory fork, adhere to Fox’s recommended maintenance intervals:

  • Every 30 hours: Clean stanchions, inspect seals, and check air pressure.
  • Every 50 hours: Lower leg service. Drain and replace bath oil, clean wipers and foam rings.
  • Every 100–125 hours or annually: Full damper and air spring rebuild including seal replacement and damper bleed.

Clean the exterior regularly with a microfiber cloth and isopropyl alcohol. Avoid power washers as they can force water past seals and contaminate internals.

Troubleshooting Common Issues

Common setup issues can compromise fork performance. Below are typical symptoms and their potential causes:

  • Harsh top-out clunk: Excess rebound damping or low air pressure.
  • Fork diving under braking: Insufficient low-speed compression.
  • Lack of travel or sticky movement: Contaminated or dry seals, worn bushings.
  • Unusual noises (squelching, clicking): Air in damper or loose internal fasteners.

Address each by reviewing the relevant setup or servicing the affected subsystem. If damping inconsistencies persist, a damper bleed may be necessary.

Customization and Performance Tuning

The Fox 40 Factory allows for significant customization through volume spacers and damper tuning. By adjusting the number of volume spacers, riders can control bottom-out resistance without affecting sag.

The GRIP2 damper, featured on the 40 Factory, supports external adjustments for:

  • High-speed compression
  • Low-speed compression
  • High-speed rebound
  • Low-speed rebound

This four-way tuning makes the fork highly adaptable to varying terrain. Riders can experiment with these settings using test rides on familiar trails, gradually adjusting and documenting changes.

Compatibility with Other Drivetrain and Frame Components

The 40 Factory is designed for DH-specific frames with a 20 mm thru-axle and 203 mm rotor standard. Ensure the axle to crown measurement (around 590 mm) and rake (48 mm) match the frame’s geometry design to avoid handling issues.

It’s also crucial to match brake mount types (Post Mount) and ensure headset compatibility with the 1.125″ to 1.5″ tapered steerer tube. Most modern DH bikes will accommodate this specification, but always double-check before purchasing.

Comparing Fox 40 Factory to Similar Forks

The 40 Factory is often compared with:

  • RockShox BoXXer Ultimate: Slightly lighter, with a DebonAir spring and Charger 3 damper.
  • Öhlins DH38 m.1: Offers plush initial stroke feel and excellent small bump sensitivity.
  • Manitou Dorado Pro: Inverted design for reduced unsprung mass but less common service support.

The Fox 40 Factory stands out for its precise damping controls, stiffness under load, and wide availability of service kits and parts. For riders prioritizing tunability and reliability, it remains a top-tier choice.

Best Practices for Long-Term Durability

To keep the Fox 40 Factory in peak condition:

  • Perform lower leg maintenance before winter storage or after wet rides.
  • Monitor for seal wear or oil weeping—early replacement prevents internal damage.
  • Store the bike with minimal fork compression to avoid air spring wear.
  • Use only Fox-approved fluids and follow the exact service steps in the user manual.

Frequently Asked Questions (FAQs)

1. How much air pressure should I run in my Fox 40 Factory fork?
Use the Fox suspension pressure chart based on your body weight and riding style. Start with the recommended PSI and fine-tune during test rides.

2. Can I install the Fox 40 Factory on a trail or enduro bike?
The 40 Factory is designed for dual crown, downhill-specific frames. It is not compatible with most trail or enduro bikes due to its axle-to-crown length and dual-crown design.

3. What oil should I use for lower leg service?
Use Fox 20wt Gold in the lower legs and Float Fluid for lubricating air seals during service.

4. When should I rebuild the damper on my Fox 40 Factory fork?
Every 100 to 125 hours of riding or annually. More frequent rebuilds may be needed under harsh riding conditions.

5. Why does my fork feel harsh even after setting sag correctly?
Check your high-speed compression damping. If it’s set too high, it may cause the fork to feel harsh on big hits. Also inspect for seal drag or dry bushings.

6. Can I convert the 40 Factory to a different wheel size?
Wheel compatibility depends on the arch clearance and axle type. The 40 Factory is typically optimized for 27.5″ or 29″ wheels depending on the model, but not all versions support both.

Conclusion

Maintaining your Fox 40 Factory fork at home is entirely achievable with the right tools and discipline. By following regular service intervals, optimizing settings for your riding style, and staying vigilant about early signs of wear, you can extend the performance life of this elite downhill fork and enjoy consistently controlled descents.