The Fox 40 Factory suspension fork is a premium, downhill-oriented fork known for its stiffness, adjustability, and smooth performance under extreme conditions. Maintaining this fork properly ensures it continues delivering high-performance responsiveness and control. This guide provides step-by-step maintenance procedures, tuning advice, troubleshooting solutions, and compatibility tips focused exclusively on the Fox 40 Factory.
Tools Required:
- 10mm, 15mm socket wrenches
- Torque wrench [paid link] (0–20 Nm)
- Suspension oil (Fox 20wt Gold, Float Fluid)
- Isopropyl alcohol (90%+)
- Clean rags and gloves
- Seal driver and pick set
- Suspension pump
- Measuring cup or syringe
- Allen keys [paid link] (2mm to 6mm)
- Small flathead screwdriver
Regular Maintenance Schedule
Routine care minimizes long-term wear and keeps performance optimal.
After Every Ride:
Wipe the stanchions and dust wipers using a clean, damp cloth. Avoid high-pressure water on seals.
Every 30 Riding Hours:
Inspect for oil residue, bushing play, or stanchion damage. Lubricate dust seals with Float Fluid.
Every 50 Riding Hours:
Perform a lower leg service. Replace bath oil, clean internals, and check for wear.
Every 125–200 Riding Hours:
Conduct a full damper and air spring overhaul. Replace wiper seals and inspect internal components.
Lower Leg Service Procedure
Servicing the lower legs restores small bump sensitivity and prevents oil contamination.
Step 1: Remove the Fork from the Bike
Loosen the axle and crown bolts. Remove the fork and place it on a clean bench.
Step 2: Drain the Bath Oil
Using a 10mm socket, loosen the bottom nuts. Use a pick to break the seal, then invert the fork and drain the oil.
Step 3: Slide Off the Lower Legs
Gently remove the lowers. Be cautious not to damage bushings or splash remaining oil.
Step 4: Clean and Reassemble
Wipe internals with isopropyl alcohol. Apply Float Fluid to foam rings. Pour 20ml of Fox 20wt Gold oil into each lower leg and reinstall. Tighten bolts to 5.1 Nm.
Air Spring Maintenance
Proper air spring care ensures predictable rebound and plushness over impacts.
Accessing the Air Spring:
Using a 2mm Allen key, remove the air cap and bleed pressure. Disassemble the top cap with a socket and remove the air shaft assembly.
Inspection and Cleaning:
Check the shaft for scratches or oil contamination. Clean the assembly, replace O-rings if worn, and lubricate with Float Fluid.
Reassembly:
Install the air shaft and torque the top cap to 26 Nm. Inflate to rider-specific pressure using a suspension pump.
Damper Maintenance Overview
Fox recommends damper maintenance be performed by experienced users or professionals. However, inspecting for performance issues like harsh rebound or damper lockout can help determine service needs.
Indicators for Damper Service:
- Inconsistent rebound speed
- Locked compression circuit
- Noise during compression strokes
General Damper Handling Tip:
Never open a sealed damper unit without proper bleed tools. If in doubt, send it to Fox for factory servicing.
Troubleshooting Common Issues
Some recurring problems can arise from improper setup or wear.
Stiction or Harsh Top-Out:
Caused by dry seals or insufficient lubrication. Perform a lower leg service and lubricate dust wipers.
Leaking Oil from Bottom Bolts:
This typically results from worn crush washers. Replace during each lower leg service.
Rebound Not Responding:
Likely a damaged damper shaft or internal blockage. Requires a full damper inspection.
Creaking at the Crown:
Loose crown bolts or bushing play may cause noise. Torque bolts to spec and inspect for wear.
Performance Tuning and Customization
Adjustments to the Fox 40 Factory can be tailored to suit different rider styles and terrain.
Air Spring Tuning:
Use volume spacers to adjust progression. More spacers yield a firmer end stroke, while fewer provide a linear feel.
Rebound Adjustment:
The red knob under the right fork leg adjusts rebound speed. Slower rebound offers more control on drops; faster rebound aids terrain tracking.
High/Low-Speed Compression:
Separate dials allow fine-tuning for brake dive, cornering, and impact resistance. Adjust these based on rider feedback and terrain roughness.
Chassis Stiffness:
Adjust the pinch bolts evenly and avoid over-torquing. Balance stiffness and compliance to improve tracking and comfort.
Compatibility with Other Components
The Fox 40 Factory uses proprietary technology and requires specific compatibility checks.
Steerer Tube and Crown:
Tapered steerer fits DH frames with 1.5” head tubes. Ensure crown race is properly seated.
Brake Mounting:
Uses 203mm post mounts. Adapters allow compatibility with 220mm rotors. Ensure caliper alignment for consistent braking.
Axle Standards:
Uses a 20x110mm Boost DH axle. Do not substitute with standard Boost or 15mm thru-axles.
Handlebar and Stem Interface:
Compatible with direct mount stems (Boxxer standard). Verify torque specs to prevent bar slippage.
Comparison with Similar Forks
Evaluating the Fox 40 Factory against other downhill forks can inform upgrade choices.
Fox 40 Factory vs. RockShox Boxxer Ultimate:
The 40 Factory offers better small bump sensitivity and damping consistency at high speeds. Boxxer is lighter and may be more forgiving for beginners.
Fox 40 Factory vs. Öhlins DH38 M.1:
Öhlins provides excellent mid-stroke support and customization, while Fox delivers better all-out speed performance and easier serviceability.
Fox 40 Factory vs. Marzocchi Bomber 58:
The Bomber 58 is a budget-friendly alternative with similar chassis design, but lacks the high-end damper technology found in the 40 Factory.
Frequently Asked Questions (FAQs)
How often should I service my Fox 40 Factory fork?
Basic lower leg service is recommended every 50 hours of riding, with full overhauls at 125–200 hours depending on conditions.
Can I use any suspension oil for my Fox 40 Factory?
No. Use only Fox-approved oils like 20wt Gold and Float Fluid to ensure compatibility and performance.
Is the Fox 40 Factory compatible with e-MTBs?
Yes, it’s suitable for high-stress applications like e-MTB downhill builds. Ensure the chassis and axle standards match.
Why does my fork feel harsh even after servicing?
Improper air pressure or damper settings may be the cause. Double-check your setup and volume spacers.
Can I install this fork myself without special tools?
Basic maintenance is possible with common tools, but damper and air spring services require specialty tools and knowledge.
Does the Fox 40 Factory support coil conversion kits?
No, the 40 Factory is an air-sprung fork only and does not support coil spring conversions.
Conclusion
The Fox 40 Factory is a race-proven downhill suspension fork that rewards attentive maintenance and fine-tuned setup. Regular service not only extends its lifespan but also keeps it responsive under pressure. By following this guide, riders can ensure their 40 Factory continues to perform at the highest level on any descent.