The Fox 40 Factory suspension fork is a high-performance downhill fork engineered for aggressive terrain and demanding riders. It’s designed to deliver superior responsiveness, precise tracking, and durable performance. However, like any precision component, the 40 Factory can develop performance issues due to improper installation, lack of maintenance, or wear and tear. This guide focuses on identifying, diagnosing, and resolving the most common issues riders may face with their Fox 40 Factory forks.
Tools Required
- Torque wrench [paid link]
- Allen key set (preferably metric)
- Suspension pump
- Shock oil (Fox recommended)
- Clean rags and isopropyl alcohol
- Seal installation tool (for lower leg service)
- Soft-jawed vise with fork mount
Incorrect Compression or Rebound Settings
Compression and rebound settings are often misunderstood, leading to poor fork performance. If the fork feels harsh over bumps or lacks support, incorrect damping is usually the culprit.
Diagnosis
- Harsh ride: High-speed compression is set too firm.
- Fork packs down: Rebound is too slow.
- Fork feels bouncy: Rebound is too fast.
Solution
- Reset both rebound and compression to the factory baseline (found in the Fox tuning guide).
- Make incremental adjustments while riding similar terrain to isolate and fine-tune.
- Use a suspension pump to adjust air pressure in the EVOL air spring for proper sag (typically 15–20%).
Excessive Stiction or Harsh Initial Stroke
If the initial stroke feels sticky or the fork hesitates to begin moving, this indicates dry or contaminated seals, or insufficient lubrication inside the lower legs.
Diagnosis
- You feel resistance when the fork begins compressing.
- There’s audible friction or “stick-slip” sensation.
Solution
- Perform a lower leg service. Drain old oil and clean internals with isopropyl alcohol.
- Inspect and replace foam rings and dust wipers if dry or damaged.
- Apply 10ml of Fox-specified suspension oil per leg before reinstalling.
- Reassemble and torque bolts to specification.
Oil Leaks from Seals
Oil leaking from the top caps or lower legs signals compromised seals, overfilled oil chambers, or incorrectly installed components.
Diagnosis
- Noticeable oil trails on stanchions.
- Reduced damping feel or air spring consistency.
- Oil dripping near the axle or arch.
Solution
- Replace dust wipers and oil seals with a fresh seal kit.
- Ensure foam rings are properly soaked in oil during reassembly.
- Do not overfill the lower legs; use precise oil measurements as specified by Fox.
- Ensure upper tubes are free of nicks or damage that may damage new seals.
Fork Bottoming Out Too Easily
If your Fox 40 Factory fork bottoms out aggressively on moderate impacts, your air spring setup or volume spacers might be incorrect.
Diagnosis
- Full travel is reached too quickly during drops or jumps.
- Harsh clunking sound on impact.
Solution
- Check air pressure; increase PSI within manufacturer limits.
- Add volume spacers (also called air tokens) to increase progression.
- Confirm that the compression settings are not too soft.
Fork Not Returning to Full Travel
The fork may feel like it’s riding lower in its travel or not extending fully after compressions. This may result from trapped air or an internal damper issue.
Diagnosis
- Travel feels limited during manual testing.
- No visible physical obstruction.
Solution
- Bleed the damper and air spring to remove any trapped air.
- Confirm negative air spring equalization by compressing fork after pumping.
- If the damper shaft is bent or damaged, it may require professional service or replacement.
Clicking or Rattling Noises During Operation
Unusual noises often indicate loose bolts, worn bushings, or internal air/oil migration.
Diagnosis
- Clicking on rebound stroke.
- Rattling sound during small bumps or vibrations.
Solution
- Check all bolts, including crown bolts and axle clamps, and torque to spec.
- Inspect for bushing play by rocking the fork fore and aft while holding the front brake.
- If bushing play exists, bushing replacement or factory service is required.
Air Loss in EVOL Air Spring
Gradual or sudden air loss in the EVOL chamber typically points to worn seals or improper valve sealing.
Diagnosis
- Fork sags overnight.
- Requires frequent air pressure top-ups.
Solution
- Check the Schrader valve for leaks using soapy water.
- Replace air spring seals during air spring service.
- Ensure cap is fully tightened after each pressure adjustment.
Brake Mount Misalignment
Rotor rub or uneven pad wear may stem from improper fork brake mount alignment.
Diagnosis
- Brakes rub even after caliper centering.
- Pads wear unevenly or prematurely.
Solution
- Verify brake mount face alignment with a facing tool if possible.
- Check torque specs on brake caliper bolts.
- Use correct post-mount adapters for rotor size compatibility.
Crown Creak or Steerer Play
If the fork emits creaking sounds or feels loose at the head tube, it may indicate a loose crown-steerer interface or headset issues.
Diagnosis
- Creaking during sprints or rough sections.
- Noticeable play when rocking the fork while holding the front brake.
Solution
- Verify headset preload and bearing condition.
- Inspect the steerer tube for cracks or wear.
- If the creak persists, the crown-steerer bond may be compromised and require replacement or warranty evaluation.
Conclusion
Maintaining the Fox 40 Factory suspension fork in peak condition demands regular servicing, proper setup, and attentive troubleshooting. By identifying early symptoms such as air loss, damping inconsistency, or structural noises, riders can avoid more serious performance degradation. Whether you’re a privateer racer or a weekend warrior, this guide ensures you can diagnose and resolve the most common Fox 40 Factory fork issues efficiently and accurately.