The Fox 40 Factory suspension fork is a premier choice for downhill and gravity riders who demand top-tier performance and precise control. Engineered with advanced features like Kashima coating, GRIP2 damper, and air spring technology, the 40 Factory requires methodical service practices to maintain its edge. Whether you’re new to fork servicing or experienced in suspension maintenance, this guide will provide you with a detailed, expert approach to servicing the Fox 40 Factory.
Tools Required
- Allen keys [paid link] (4 mm, 5 mm, 6 mm)
- Torque wrench [paid link]
- Suspension oil (Fox 20wt Gold, Float Fluid)
- Suspension grease
- Clean rags and isopropyl alcohol
- Oil pan or drain tray
- Syringe or oil measuring device
- Pick or seal puller
- Soft mallet
- Suspension pump
Installation Best Practices
The installation of the Fox 40 Factory must be done with care to ensure safe and optimal operation. Begin by verifying that your frame accepts dual-crown forks and that your headset is compatible with the steerer tube diameter. The steerer must be cut precisely, allowing enough room for headset spacers and the stem clamp. Install the crown race using a race installer and torque the stem bolts as specified.
The fork legs should be aligned properly to avoid stanchion binding. This involves evenly torquing the axle and pinch bolts, with the front wheel correctly seated in the dropouts. During installation, make sure the brake caliper mounts line up with the disc rotor to prevent misalignment, which could lead to brake rub or uneven pad wear.
Initial Setup and Adjustment
The Fox 40 Factory is equipped with a GRIP2 damper and adjustable air spring, making tuning crucial for optimal performance. Begin by setting sag using a suspension pump. Fox recommends approximately 15–20% sag for downhill use, adjusted through the air pressure valve. The damper features high- and low-speed compression as well as rebound adjusters. Turn each dial to the manufacturer’s baseline setting and fine-tune according to rider weight, terrain, and riding style.
Ensure equal air pressure between the positive and negative chambers by cycling the fork several times after pressurizing. This avoids uneven travel response and potential harshness. Check that the rebound is slow enough to prevent pogo effects but fast enough to keep the front wheel tracking over rapid terrain changes.
Routine Maintenance Schedule
To maintain top performance, routine maintenance is essential. Fox recommends lower leg service every 40 riding hours and a full damper and air spring overhaul at 100 hours. Clean external surfaces regularly and inspect for oil seepage or contamination around the seals and stanchions. Use only suspension-safe cleaners and avoid high-pressure water near the fork seals.
During the 40-hour service, remove the lower legs, drain the old bath oil, and inspect for contamination. Clean the inside of the lowers and inspect the foam rings and wiper seals. Replace them if worn or contaminated. Reapply fresh Fox 20wt Gold oil and reassemble the fork to the correct torque values. Always cycle the fork after reassembly to ensure oil distribution and correct damping function.
Common Setup and Performance Issues
Several issues may arise with the Fox 40 Factory if improperly set up. One common problem is excessive dive under braking, which often results from insufficient compression damping or too low air pressure. Increasing low-speed compression or adding volume spacers can help maintain ride height.
Harsh bottom-outs suggest inadequate air pressure or too few volume spacers. In contrast, if the fork feels unresponsive over small bumps, consider reducing compression damping or lowering air pressure slightly to increase sensitivity.
A sticking fork or inconsistent rebound action may indicate contamination in the damper or worn seals, necessitating immediate servicing. Always inspect for signs of stanchion wear or scratches, which can allow dirt intrusion and further damage.
Customization and Performance Optimization
For riders seeking to tailor the Fox 40 Factory beyond stock settings, several options are available. Volume spacers can be added or removed to change spring curve progression. More spacers increase ramp-up, useful for aggressive riders who want to avoid bottoming out. Fewer spacers allow a more linear feel, preferred by lighter or less aggressive riders.
The GRIP2 damper allows in-depth customization. For bike park riding with consistent terrain, a stiffer setup with increased compression may provide better support. For technical trails, softening rebound and reducing high-speed compression helps maintain traction.
Kashima-coated stanchions reduce friction and wear, but performance can further be enhanced by applying high-quality suspension-specific grease during rebuilds. For riders seeking a more sensitive initial stroke, upgrading seals to low-friction aftermarket options may provide marginal gains.
Compatibility Considerations
The Fox 40 Factory is designed primarily for use with DH and gravity-oriented frames. It is not compatible with frames designed for single-crown forks due to the dual-crown design. The axle is 20 mm thru-axle, requiring compatible hubs.
Brake caliper mounts are Post Mount 203, limiting compatibility to larger rotor sizes unless adapters are used. The steerer tube is a 1.125” straight format transitioning to 1.5” at the crown, requiring a tapered headset or reducer cups depending on your frame.
It is compatible with most modern downhill handlebars and stems using direct mount standards. When matching with rear shocks or drivetrain setups, always tune both ends of the bike to maintain balanced suspension characteristics.
Model Comparison: 40 Factory vs. 40 Performance Elite
While both the Factory and Performance Elite versions share core internals, the Factory stands out with its Kashima coating and optional air spring upgrades. The GRIP2 damper is shared, but the Performance Elite forgoes the premium anodized finish. This results in slightly higher stiction and marginally increased wear over time.
Weight is similar, though the Factory version may edge slightly ahead due to material selection. From a performance perspective, both offer near-identical damping characteristics when tuned equally. However, riders prioritizing durability and ultimate performance may find the Factory’s enhancements worth the investment.
Frequently Asked Questions
How often should I service my Fox 40 Factory fork?
Service the lower legs every 40 hours and perform a full overhaul at 100 hours. Regular cleaning and inspection are advised after every ride.
Can I use a different brand’s oil in the Fox 40 Factory fork?
It is strongly recommended to use Fox-specific suspension fluids like 20wt Gold and Float Fluid. Using other oils may compromise damping consistency and seal compatibility.
What’s the ideal sag for the Fox 40 Factory?
Target 15–20% sag based on your fully geared riding weight. This provides a good balance between small bump compliance and support under load.
Why is my fork making a knocking noise during compression?
This could be caused by worn bushings, insufficient bath oil, or damper issues. A full inspection and service are recommended to prevent further damage.
Can I upgrade the air spring on the Fox 40 Factory?
Yes, you can install a new air spring assembly from Fox to change travel or improve tuning. Always use compatible parts from Fox to maintain performance and safety.
Is the Fox 40 Factory suitable for enduro riding?
Due to its weight and dual-crown design, it is not recommended for enduro. It excels in DH and gravity-specific scenarios where strength and damping performance are critical.