Performing an oil change on your Fox 38 Rhythm suspension fork is a crucial part of regular maintenance that ensures optimal performance, responsiveness, and longevity. This guide provides a complete step-by-step procedure, tailored specifically for the 38 Rhythm model, to help you carry out a clean and precise oil service. The process outlined here will address installation of new oil, cleaning techniques, compatibility notes, and performance enhancements.
Tools Required
- 10mm and 6mm Allen wrenches [paid link]
- Torque wrench [paid link] (Nm scale)
- Suspension-specific oil (Fox 20wt Gold for lower legs)
- Clean oil syringe or measuring cup (marked in mL)
- Seal pick or plastic hook tool
- Suspension grease (e.g., Slick Honey or equivalent)
- Nitrile gloves
- Clean rags and isopropyl alcohol
- Oil pan or catch tray
- Plastic mallet
Understanding the 38 Rhythm’s Oil System
The Fox 38 Rhythm uses a lower leg bath lubrication system. Unlike damper-side only oil forks, this model benefits from oil located in both lower legs, which reduces stiction and protects internal bushings. The recommended oil volume is 40 mL per leg, and only Fox 20wt Gold oil should be used unless otherwise specified.
The air spring side and damper side each have distinct functions: the air spring provides support and travel feel, while the damper controls rebound and compression. The oil change does not typically involve damper disassembly unless you’re also performing a full service.
Preparation Before Oil Change
Start by removing the front wheel and brake caliper from the fork. Carefully remove the axle and slide the wheel out. Then, release all air from the fork via the Schrader valve on the left leg to avoid pressure-related accidents during disassembly.
Clean the fork thoroughly using a rag and isopropyl alcohol, focusing on the lower legs, seals, and bolts. This prevents contamination during reassembly. Place the fork upside down in a stand or secure position with the lowers pointing downward and the crown stable.
Draining the Old Oil
Unscrew the 10mm and 6mm bolts from the bottom of each lower leg. A light tap with a plastic mallet may be necessary to release the leg if the oil seals have seized. Once both bolts are removed, carefully slide the lower legs down and off the stanchions, letting the old oil drain into a pan.
Clean the interior of the lower legs with alcohol and rags. Remove any dirt or debris near the wiper seals. Avoid using sharp tools that may scratch the inside surfaces. Inspect foam rings under the seals; replace or clean and soak them in fresh oil before reinstalling.
Installing New Oil
With the lower legs clean, apply a thin layer of suspension grease around the inside of the wiper seals. This eases reinstallation and improves sealing. Also apply grease to the foam rings.
Slide the lower legs back onto the stanchions, making sure not to dislodge the foam rings. Before pushing them all the way up, use a syringe or measuring cup to add 40 mL of Fox 20wt Gold oil into each leg through the open bolt holes at the bottom.
Once the oil is added, gently push the lowers fully onto the stanchions and align the bolt holes. Reinsert the 10mm and 6mm bolts and tighten to the factory-recommended torque spec: typically 7.3 Nm. Confirm with Fox’s latest service manual for your fork’s production year.
Post-Installation Checks
After reassembly, inflate the air spring to your desired pressure, based on your weight and riding style. Reinstall the brake caliper and front wheel, making sure all bolts are tightened to spec. Cycle the fork through its travel by compressing it several times. This helps distribute the oil evenly inside the lowers.
Check for leaks around the wiper seals and bottom bolts. If oil seeps out after a few compressions, recheck torque and seal integrity. Clean any oil residue off the exterior and allow the fork to sit upright for several minutes to settle the oil.
Common Setup Issues and Troubleshooting
Users sometimes experience a knocking sound after service. This usually results from insufficient oil volume or trapped air in the lowers. Cycling the fork a few times typically resolves it. If not, open the fork and recheck oil levels.
Another frequent issue is stiff initial travel, caused by dry or over-tightened wiper seals. Ensure seals are greased properly and not overly compressed during installation.
If oil leaks persist after a proper change, inspect the crush washers on the lower bolts or consider replacing the wiper seals entirely.
Optimizing Performance After the Oil Change
Changing the oil restores factory-smooth action, but additional gains can be made. Use a small amount of low-friction suspension grease on the stanchions for smoother small-bump compliance. Tuning air pressure and rebound settings after the oil change will also help personalize ride feel.
Allow at least one ride to break in the fresh oil. It may feel slightly sticky initially but will smooth out as the components re-lubricate.
Compatibility and Service Intervals
The 38 Rhythm fork is compatible only with Fox-specific oil grades and volumes. Avoid mixing brands or viscosities, as this can affect damping characteristics.
Fox recommends a lower leg service—including oil change—every 30-50 hours of riding. Frequent riders or those in muddy conditions should perform it more often. This schedule prolongs fork life and maintains consistent damping.
Comparison with Other Fox Fork Models
Compared to the 38 Factory and Performance Elite models, the 38 Rhythm uses a simpler GRIP damper and non-Kashima coated stanchions. This makes maintenance easier but slightly reduces performance under aggressive use. However, the oil change procedure remains largely the same across models, with differences primarily in damper architecture and material coatings.
Riders looking for top-tier responsiveness may prefer the Factory model, but the Rhythm remains an excellent, serviceable option for enduro and trail riding.
Frequently Asked Questions (FAQs)
1. How often should I change the oil in my Fox 38 Rhythm fork?
Every 30-50 hours of riding time. More frequent service is advised in wet or dusty conditions.
2. Can I use any suspension oil for this fork?
No. Only use Fox 20wt Gold oil to ensure proper lubrication and damping characteristics.
3. Is a full damper rebuild required during an oil change?
No. A basic oil change involves only the lower legs. The damper remains sealed unless full service is needed.
4. My fork feels sticky after oil change. Is this normal?
Yes, initially. The seals and foam rings need time to re-lubricate. Ride a few times and it should smooth out.
5. Can I do this without a torque wrench [paid link]?
It is not recommended. Proper torque ensures bolts stay secure without damaging threads or causing leaks.
6. Is the 38 Rhythm oil change process the same as for the 36 or 34 models?
No. While similar in concept, each model has specific oil volumes and bolt configurations. Always refer to the specific fork’s manual.