The Fox 40 Factory fork is a premium downhill suspension fork designed for aggressive riding and top-tier performance. Regular maintenance ensures that this high-performance component continues to operate smoothly and reliably. This guide covers everything from basic servicing and routine maintenance to deeper servicing practices, all tailored specifically for the Fox 40 Factory.
Tools Required
- 10mm socket wrench
- 2mm, 5mm, and 6mm Allen keys [paid link]
- Torque wrench [paid link] (adjustable up to 20 Nm)
- Clean rags and isopropyl alcohol
- Suspension-specific grease and fork oil
- Oil syringe or measuring cup
- Soft-faced mallet
- Pick tool or seal puller
- Dust wipers and foam rings (Fox 40-specific)
- Genuine Fox 20wt Gold oil
- Suspension stand or stable workbench
Understanding the 40 Factory’s Design
The Fox 40 Factory uses a dual-crown chassis with a high-volume air spring and a high-speed/low-speed compression and rebound damper. Its GRIP2 damper provides precision adjustability and the EVOL air spring enhances small bump compliance. This design supports aggressive downhill use, and maintaining it requires attention to the damper, air spring, and lower leg service intervals.
Routine Lower Leg Service (Every 30-50 hours)
This service maintains lubrication and prevents debris buildup.
Step-by-step process:
Remove the wheel and brake caliper, then loosen and remove the axle. With the fork inverted, release air pressure from the air spring using the valve under the top cap. Loosen the lower leg bolts with a 10mm socket but do not remove them fully. Tap them gently with a mallet to unseat the legs, then slide the lowers off carefully over a bucket to catch old oil.
Clean the internals with isopropyl alcohol and inspect the foam rings and wipers. Replace them if worn. Soak new foam rings in 20wt Gold oil before installation. Reinstall the lower legs, aligning carefully to avoid damaging the seals. Inject the recommended amount of oil into each leg via the bath oil ports. Torque the bolts to spec and re-pressurize the air spring.
Full Air Spring Service (Every 100 Hours)
Air spring servicing is crucial for smooth performance and proper sag setup.
Remove the top cap using a 6mm Allen key. Carefully extract the air shaft assembly using internal retaining tools. Inspect all o-rings and seals for wear or deformation. Replace the air piston seal and shaft o-rings using the Fox 40 rebuild kit. Lightly lubricate all components with suspension grease during reassembly. Reinstall the air shaft, torque to spec, and refill air to your desired pressure.
Damper Service (Every 125-200 Hours)
Due to the complexity of the GRIP2 damper, this should be performed by experienced mechanics, but an advanced home mechanic can complete it with the right tools.
Start by removing the damper from the right stanchion leg. Using a seal bullet, carefully disassemble the damper side. Drain and discard used damper oil. Inspect the shim stack, bladder, and piston for any signs of scoring or wear. Replace the bladder if it shows swelling or deformation. Refill the damper with the correct volume of damper fluid, following Fox’s bleed instructions for the GRIP2 system. Reassemble and torque all bolts accurately.
Troubleshooting Common Issues
Loss of Travel or Harsh Feel:
Likely due to low air pressure or worn air spring seals. Check for correct sag and rebuild the air spring if necessary.
Oil Leaking from Seals:
Usually indicates degraded wiper seals. Replace the dust wipers and foam rings during a lower leg service.
Clicking or Unstable Rebound:
This may come from improper damper oil levels or internal wear. A full damper service and oil replacement should resolve it.
Inconsistent Compression Adjustment:
Often caused by damaged adjuster knobs or internal valve issues. Disassemble and inspect the compression valve stack for wear or blockage.
Optimization and Custom Tuning
The Fox 40 Factory offers external adjustments including high-speed and low-speed compression, rebound, and air pressure tuning. Riders can optimize performance by:
- Matching spring rate to rider weight and terrain style.
- Fine-tuning rebound for better traction over technical terrain.
- Adjusting high-speed compression to reduce harsh bottom-outs.
- Using volume spacers to personalize ramp-up characteristics in the air spring.
Experimenting with these settings will refine performance but always make one change at a time and document settings for consistent results.
Compatibility with Other Drivetrain and Frame Components
The Fox 40 Factory uses a 20mm thru-axle and is compatible with 200mm and larger brake rotors, using post-mount adapters. It’s primarily designed for 29-inch wheels but certain 27.5″ models exist. Ensure the headtube diameter accommodates dual-crown forks and check frame clearance before installation. It pairs well with Shimano Saint or SRAM Code calipers and downhill drivetrain setups like SRAM X01 DH or Shimano Zee/Saint.
Comparison with Similar Forks
When compared to other downhill forks like the RockShox Boxxer Ultimate or Öhlins DH38, the Fox 40 Factory offers:
- Superior small bump sensitivity due to the EVOL air spring.
- More precise external tuning thanks to the GRIP2 damper.
- Slightly more involved servicing compared to simpler damper systems.
- Greater aftermarket support and documentation.
Riders prioritizing adjustability and performance over simplicity will prefer the Fox 40 Factory. Those who value lighter maintenance cycles might consider simpler damper systems.
FAQs
Q1: How often should I service the Fox 40 Factory fork?
A lower leg service is recommended every 30-50 hours, while air spring and damper services are suggested at 100 and 125-200 hours respectively.
Q2: Can I use any suspension oil in my Fox 40 Factory?
No. Only use Fox 20wt Gold for bath oil and the specified damper fluid to maintain damping performance and avoid seal degradation.
Q3: Do I need special tools to service the air spring?
You’ll need a torque wrench [paid link], pick tool, and suspension-specific grease. A seal bullet is also recommended to avoid damaging o-rings during reassembly.
Q4: What’s the best air pressure setting for my Fox 40 Factory fork?
It depends on rider weight and terrain. Fox provides a tuning guide, but experimentation is key. Start with 70-80 psi for a 160-180 lb rider and adjust as needed.
Q5: Can I upgrade a Performance model to Factory specs?
Not entirely. While you can swap dampers or add Kashima-coated stanchions, it is more cost-effective to buy the Factory model outright.
Q6: Is the Fox 40 Factory compatible with eMTBs?
Yes, it is rated for use on certain eMTB downhill platforms, provided the frame and geometry are compatible with dual-crown forks.
Servicing the Fox 40 Factory suspension fork at home requires precision, patience, and the right tools. By following these detailed steps, riders can maintain optimal performance, extend fork longevity, and ensure a smoother, more responsive ride.