The Fox 40 Factory suspension fork is a high-performance, dual-crown downhill fork engineered for aggressive riding and elite-level control. Maintaining this component is essential for optimal performance and longevity. A routine oil change helps preserve damping consistency, protect internal components, and ensure smooth suspension action. This guide focuses specifically on how to perform a correct oil change for the Fox 40 Factory model.
Tools Required
- 10 mm and 5 mm hex wrenches
- Torque wrench [paid link] with Nm scale
- Soft mallet
- Oil catch pan
- Suspension-specific syringe or graduated beaker
- Clean microfiber cloths
- Suspension-specific fork oil (refer to Fox specs for weight and volume)
- Isopropyl alcohol (90% or higher)
- Nitrile gloves
- Fox-approved Slick Honey or similar fork grease
- Fox 40 Factory service manual (recommended for reference)
Understanding the Fox 40 Factory Suspension System
The Fox 40 Factory fork utilizes a GRIP2 damper and a FLOAT EVOL air spring system. These components are sealed and rely on precise oil levels to function correctly. The damper side controls compression and rebound, while the air spring side ensures smooth actuation. Regular oil changes prevent contamination and loss of damping efficiency, especially under demanding downhill conditions.
Preparation Before Starting
Begin by securing the bike in a work stand. Ensure the fork is completely deflated using the air valve to avoid internal pressure buildup during service. Remove the front wheel and brake caliper to access the fork legs. Lay down an oil-absorbent mat beneath the fork to catch any spills. It’s crucial to maintain a clean work environment, as contaminants can compromise fork internals.
Step-by-Step Fork Oil Change Procedure
Removing the Lowers
Start by loosening the pinch bolts on the fork axle and removing the axle to free the front wheel. With a 10 mm hex wrench, unscrew the bottom nuts from both fork legs. Lightly tap the bolts with a soft mallet to dislodge the foot studs from the lower legs. Once loosened, carefully slide the lower legs off while capturing residual oil in an oil pan.
Draining the Old Oil
Tilt the fork downward and allow all old oil to drain completely. Be patient during this step to ensure full evacuation of the contaminated fluid. Wipe the fork stanchions and interior of the lower legs using a lint-free microfiber cloth soaked in isopropyl alcohol. Avoid scratching internal surfaces during cleaning.
Cleaning and Inspection
Inspect the dust wipers and foam rings for signs of wear or debris buildup. Replace these components if they appear degraded. Re-lubricate foam rings using suspension oil and apply a light coating of Slick Honey to the wiper seals. Ensure stanchions are free of nicks or scoring that could damage the seals.
Refilling and Reassembling
Use a suspension syringe to measure and insert the specified volume of oil into each leg—Fox typically recommends 20cc in the damper side and 40cc in the air spring side (check current specifications). Carefully slide the lower legs back onto the stanchions, ensuring alignment with the foot studs. Reinstall and torque the bottom bolts to the manufacturer’s recommended specification, typically around 7 Nm.
Reinstall the axle, brake caliper, and front wheel. Inflate the air spring to your preferred riding pressure and check for proper rebound and compression response. Perform a basic bounce test to ensure smooth travel and damping performance.
Troubleshooting Common Set-Up Issues
After servicing, you might experience minor setup issues:
- Sticky initial stroke: Often due to inadequate lubrication; recheck wiper seals and foam ring saturation.
- Harsh bottoming: May indicate low oil volume in the damper leg or insufficient air pressure.
- Uneven travel: Could be caused by incorrect reinstallation or trapped air in the damper circuit.
A quick reinspection and oil level verification typically resolve these issues. Always verify pressure using a digital shock pump and confirm proper rebound damping via the adjuster knobs.
Performance Optimization Tips
Enhancing your Fox 40 Factory’s performance post-oil change is possible with some targeted adjustments:
- Dial in low-speed compression to prevent dive on technical descents.
- Adjust high-speed rebound to better absorb fast hits and maintain wheel traction.
- Monitor sag using Fox’s recommended percentage (typically 15–20% of total travel).
Regular servicing (approximately every 30–40 riding hours) maximizes responsiveness and helps prevent premature wear of internal seals.
Compatibility Considerations
The Fox 40 Factory is compatible with both 27.5” and 29” wheel sizes depending on the chassis version. Ensure your fork’s axle spacing (typically 20×110 Boost) matches your hub standard. Internally, only use Fox-approved suspension fluids to maintain damping consistency and avoid seal degradation. Mixing brands or fluid weights can result in unpredictable suspension behavior.
Model Comparison
When compared to similar models like the RockShox BoXXer Ultimate or DVO Onyx DC, the Fox 40 Factory offers:
- Superior small-bump sensitivity due to its GRIP2 damper.
- Improved adjustability, offering both high- and low-speed compression and rebound.
- Factory Kashima coating, which reduces stiction and enhances durability.
However, riders focused on lighter chassis or easier serviceability might prefer simpler alternatives like the BoXXer Select.
Conclusion
An oil change on the Fox 40 Factory suspension fork is a critical maintenance task that boosts performance and preserves the fork’s internal systems. By following the correct procedure, using the right tools, and respecting torque specifications, even a home mechanic can perform a professional-quality service. Regular maintenance ensures you’ll continue to enjoy the full potential of this elite-level downhill fork.