The Fox Float 40 Factory eMTB suspension fork is a premium component engineered for aggressive electric mountain bike riding. Over time, routine wear and contamination of internal components can compromise its performance. Rebuilding the Float 40 ensures the longevity and responsiveness of your fork, restoring its factory-level smoothness and damping control. This guide provides a complete technical walkthrough of the rebuild process, including installation, tuning, and troubleshooting specific to the Float 40 Factory eMTB model.
Tools Required
- 32 mm socket
- 10 mm socket or nut driver
- 2 mm and 5 mm hex wrenches
- Torque wrench [paid link] (in Nm)
- Oil height gauge
- FOX 20wt Gold and Float Fluid
- Clean nitrile gloves
- Suspension grease
- FOX seal driver kit
- Rubber mallet
- Clean workspace with vice and soft jaws
Disassembly and Lower Leg Removal
Begin by removing the Float 40 Factory fork from the bike. Carefully clean the fork legs and crown to prevent dirt from entering the internals during disassembly. Unthread the air top cap using a 32 mm socket. Release all air from the positive and negative chambers.
Next, use a 2 mm hex wrench to loosen the rebound adjuster knob, exposing the lower leg bolts. Use a 10 mm socket to remove these bolts, then gently tap them with a rubber mallet to disengage the foot nuts. Once the lower legs are loose, slide them off the uppers slowly, watching for residual bath oil.
Inspect the removed lower legs for wear on the bushings and internal coating. Replace them if there are signs of scoring or deep contamination.
Damper and Air Spring Inspection
The Float 40 Factory features a sophisticated GRIP2 damper and an EVOL air spring system. Carefully remove the damper shaft using a 5 mm hex wrench while securing the crown in a vice with soft jaws. Slowly withdraw the shaft and check for oil discoloration or degraded seals.
For the air spring, remove the top cap completely and withdraw the shaft. Inspect the piston ring, air seal head, and negative transfer port. These parts often show signs of wear or debris buildup after extended rides. Replace all O-rings and grease the piston shaft lightly before reassembly.
Ensure the internal channels are free of obstruction. Use a lint-free cloth to clean inside the stanchion tubes and verify no scoring or pitting exists on the inner walls.
Seal Replacement and Lower Leg Preparation
Use the FOX-specific seal driver kit to remove old wiper seals and foam rings from the lower legs. Clean thoroughly using isopropyl alcohol and dry completely. Place fresh foam rings and soak them in FOX 20wt Gold oil for at least 10 minutes before installation.
Install new dust wipers using the correct diameter seal driver. Ensure the seals seat evenly without damage. Grease the inside of the dust wipers lightly with suspension grease to ease reassembly.
Fill each lower leg with the recommended bath oil quantity—typically 40 cc in each leg for the Float 40 Factory. This lubrication is crucial for small bump compliance and long-term bushing durability.
Reassembly and Oil Fill
With the damper and air spring shafts reinserted and torqued to specification, carefully slide the lower legs back onto the stanchions. Be sure the foam rings are fully seated, and the oil does not spill out.
Align the foot nuts with the damper and air spring shafts, then torque them to the factory-recommended setting (usually around 7.3 Nm). Reinstall the rebound adjuster knob and secure it with the 2 mm hex bolt.
Refill the air spring with the appropriate pressure for your weight and riding style. Remember to cycle the fork a few times while pressurizing to equalize the negative chamber. Check for leaks around the seals and damper side.
Rebound and Compression Adjustment
Set the rebound using the red dial at the bottom of the right leg. For a base tune, begin with 8 clicks out from fully closed. Adjust to suit terrain and rider preference.
On the GRIP2 damper, adjust high-speed and low-speed compression using the crown-mounted dials. Begin with the manufacturer’s base tune (typically 4 clicks out for high-speed and 10 for low-speed). Fine-tune based on trail feedback and performance.
Troubleshooting Post-Rebuild Performance
If the fork feels sticky or unresponsive, confirm that seals are properly installed and that the bath oil quantity is correct. A too-tight dust wiper can restrict small bump sensitivity.
Excessive rebound noise or poor return speed often indicates air trapped in the damper or a damaged internal shim. Re-bleed or replace the damper cartridge if symptoms persist.
Air leaks near the Schrader valve suggest worn O-rings. Replace these and ensure the valve core is tight. For sag inconsistencies, verify air equalization in both chambers.
Performance Tuning and Customization
Upgrading to a custom air spring volume spacer kit allows riders to fine-tune ramp-up characteristics. Reducing volume increases mid-stroke support and bottom-out resistance—ideal for aggressive eMTB use.
Installing a firmer or lighter spring rate (if using a coil conversion kit) can tailor performance to rider weight. The GRIP2 damper is also compatible with upgraded internal cartridges for enhanced sensitivity.
Riders may also benefit from custom low-friction SKF seals or using proprietary suspension grease with better heat resistance for long descents.
Comparing Float 40 Factory to Other FOX Forks
Compared to the FOX 38 Factory, the Float 40 is stiffer, with increased travel and dual-crown construction. It’s designed explicitly for downhill and eMTB gravity use.
While the FOX 36 offers more versatility for trail and enduro, it lacks the torsional rigidity and tunable damping range of the Float 40. Riders seeking uncompromising downhill control will find the 40 Factory the superior option.
Compatibility with eMTB Drivetrains and Frames
The Float 40 Factory eMTB fork is compatible with 29” wheelsets and boost spacing (110 mm hub width). It’s engineered for frames with tapered head tubes and adequate downtube clearance.
It pairs seamlessly with full-power eMTBs requiring additional stiffness up front. Ensure your frame accommodates the 203 mm rotor mount and accepts dual-crown fork lengths before installation.
This fork supports internally routed front brake cables via guide clips and is compatible with most modern eMTB headsets and spacers.
FAQs
1. How often should I rebuild my Float 40 Factory fork?
For regular riders, a lower leg service every 30 hours and full rebuild every 100 hours is recommended. Dusty or wet conditions may shorten these intervals.
2. Can I upgrade my Float 40 to a coil spring?
Yes, FOX and third-party manufacturers offer coil spring conversions for the Float 40 Factory. Be sure to match spring rate and compatibility with your weight and riding style.
3. Why is my fork losing air after service?
This is often due to improperly seated seals or a damaged Schrader valve. Recheck O-ring condition and use a torque wrench [paid link] when reassembling.
4. Is the GRIP2 damper user-serviceable?
While advanced users can service the GRIP2 damper, FOX recommends sending it to an authorized service center due to the complexity and need for vacuum bleeding.
5. What oil should I use in the Float 40 bath and damper?
Use FOX 20wt Gold oil for the lower leg bath and FOX proprietary damper oil for internal damping circuits. Substitutes can affect performance and seal integrity.
6. Can I install the Float 40 Factory on a non-eMTB bike?
While possible, it’s overbuilt for non-electric bikes unless used for pure downhill racing. Its weight and dual-crown design are optimized for eMTB torque and mass.