The Fox 38 Rhythm is a robust and performance-focused suspension fork designed for aggressive trail and enduro riding. Built on the same chassis as higher-end 38 series forks, the Rhythm version uses a GRIP damper and a simplified internal structure for durability and ease of service. This article will walk you through the complete rebuild process, focusing specifically on the 38 Rhythm model. From disassembly and seal replacement to reassembly and fine-tuning, this guide is tailored for riders and mechanics aiming to restore optimal fork performance.
Tools Required
- 10mm and 32mm sockets
- Torque wrench [paid link] (Nm specific)
- Soft-jawed vise
- Seal driver tool specific to 38mm stanchions
- Pick tool
- Suspension-specific grease (e.g., Fox Float Fluid, Slickoleum)
- Isopropyl alcohol (90% or higher)
- Clean lint-free cloths
- Replacement dust wipers and foam rings (38mm-specific)
- Suspension oil (Fox 20wt Gold and damper-specific fluid)
- Syringe or oil bath measuring cup
- Retaining ring pliers
Disassembling the 38 Rhythm Fork
Begin by removing the fork from the bike and securing it in a soft-jawed vise. Loosen the top caps using the 32mm socket. Before removing them completely, make a note of the air pressure and any compression settings. This helps restore the fork to its previous configuration after reassembly.
Carefully release air from the air spring side. On the damper side, unscrew the foot bolt and allow oil to drain fully into a pan. For the air spring leg, also remove the foot bolt to release any residual oil and air.
After draining, use a rubber mallet to tap the footbolts gently, freeing the lowers from the stanchions. Pull the lowers off with even force, avoiding side loads that could scratch the stanchions.
Cleaning and Inspection
Once the lower legs are separated, thoroughly clean them with isopropyl alcohol and a clean cloth. Use a pick tool to carefully remove the foam rings and dust wipers. Clean out the internal surfaces and inspect for any wear, scoring, or contamination.
Inspect the stanchions and internal components. Any significant damage to the anodizing or warping may necessitate professional service or component replacement.
Check for bushing play by inserting the stanchions back into the lowers without oil. Any noticeable lateral movement indicates worn bushings.
Replacing Seals and Foam Rings
Lubricate new foam rings with suspension oil and install them into the lower legs. Press new dust wipers using the 38mm-specific seal driver. Ensure the wipers are fully seated without distortion.
Apply a thin layer of suspension grease inside the dust wipers and along the upper bushing area. This step reduces stiction and enhances fork sensitivity.
Reassembling the Lower Legs
Slide the lower legs carefully back onto the stanchions. Ensure the foam rings remain seated and aligned. Avoid forcing the lowers if they don’t slide on smoothly—recheck seal positioning if needed.
Add the specified amount of 20wt Gold oil to each leg through the foot bolt openings. The air spring side typically requires more volume than the damper leg. Use a syringe for accuracy.
Reinstall and torque the foot bolts to Fox’s recommended specifications. Common torque for these bolts is around 7 Nm, but always refer to the latest Fox service manual for exact values.
Air Spring and Damper Top Cap Service
Remove the air spring top cap using a 32mm socket and inspect the internal seals. Reapply grease to the piston assembly and O-rings. Replace any worn or cracked parts.
On the damper side, do not attempt a full damper rebuild unless you have the tools and experience. Instead, perform an oil change or bleed using the bleed port, if applicable.
Torque both top caps securely and inflate the air spring to the previously recorded pressure. Cycle the fork to check for smooth travel and top-out behavior.
Fine-Tuning and Reinstallation
Reinstall the fork on the bike and torque all bolts per manufacturer specs. Check for proper alignment of the axle and brake caliper.
Adjust rebound and compression settings to suit rider preference. Test the fork’s movement through its travel and inspect for leaks or odd noises. Allow a short bedding-in period before aggressive riding.
Troubleshooting Common Issues
Excessive top-out noise: Indicates insufficient oil in the air spring or damper leg. Recheck oil volumes.
Stiction or slow rebound: Can stem from dry or incorrectly installed wiper seals or bushings.
Oil leaks around seals: Suggest improper seal seating or damaged stanchions.
Fork not achieving full travel: May be due to air spring binding or excessive grease/oil.
Clicking noises during compression: Typically caused by air spring piston movement or loose foot bolts.
Performance Optimization Tips
For riders seeking better sensitivity, consider upgrading the wiper seals to low-friction aftermarket versions. Periodic application of a thin layer of suspension lube on the stanchions before rides can also reduce seal friction.
Another option is revalving or upgrading the GRIP damper to a higher-performance GRIP2 if compatibility allows. This provides more adjustment options and better terrain compliance.
Use only recommended Fox oils and fluids to ensure proper internal damping and spring function. Avoid mixing fluid types between service intervals.
Compatibility Considerations
The Fox 38 Rhythm is specifically compatible with GRIP dampers and Float EVOL air springs. It shares its 38mm chassis with Factory and Performance Elite models, allowing some part interchangeability.
Ensure axle diameter (typically 15×110 Boost) and crown race diameter match your bike’s frame and headset specifications. The Rhythm fork supports both 27.5″ and 29″ wheel sizes but verify travel and offset to maintain geometry integrity.
Comparing 38 Rhythm to Similar Forks
The 38 Rhythm stands out due to its value-focused build using the same chassis as higher-end 38 models but with simplified internals. Compared to the Fox 36, it provides more stiffness and travel support, ideal for heavier or more aggressive riders.
The GRIP damper, while less adjustable than the GRIP2, is easier to maintain and highly reliable. For budget-conscious riders, the 38 Rhythm provides top-tier chassis performance at a mid-range price point.
Compared to RockShox ZEB Select, the 38 Rhythm offers better small bump sensitivity but fewer adjustment options. However, it shines in consistency and ease of rebuilds.
Conclusion
Rebuilding the Fox 38 Rhythm suspension fork restores performance and extends longevity. By following a structured, methodical approach, you can ensure your fork continues to perform at its best across rough terrain. Attention to oil volumes, seal installation, and correct torque settings is crucial. With periodic service and proper care, the 38 Rhythm can deliver years of reliable trail performance.