How to do a 50hr service on your FOX fork

50-Hour Lower-Leg Service: Fox forks (GRIP Series) — With S4 DIY Kit

GET YOUR KIT HERE!

Regular lower-leg service keeps your fork feeling supple, protects bushings and stanchions, and extends service intervals. This guide walks you through the Lower Leg(50 hour) service in a step by step process to insure your success. This process can be done with minimal tools that you can typically source around the house. If you have the proprietary tools from Fox to dislodge the foot studs( #’s 398-00-682/398-00-681) please use them but in this guide we will perform the service without them to show how it can be done without expensive tools. With that said, *we ALWAYS recommend using the proper tool for the job*

Safety first: wear eye protection and gloves; mind oil disposal. We also recommend PPE during service.

Pro tips from the bench

Don’t scratch anything. Any nick on the stanchion or seal bore can cause chronic leaks.
Consistent oil. Room-temp bath oil flows and measures more consistently.
Always use fresh crush washers. Reusing can cause seepage.
Seal driver matters. A proper driver prevents cocked wipers and premature wear.
Clicks & PSI log. Noting your settings in your phone can help in future tuning.

When to stop and call S4

If you see metallic glitter in the oil, feel bushing play (clunk with fore-aft rock), notice a crooked wiper bore, or have damper shaft rebound issues, pause and bring it to S4 for inspection or a damper/air-spring rebuild.

____________________________________________________________________________

What you’ll need

From the S4 50-hour DIY kit

Dust wipers
Foam rings
Crush washers (x2)
Bath oils (see “Fluids” below)
Suspension grease
Seal driver

(Your S4 kit bundles the same quality parts S4 techs use.)

Tools

Torque wrench (in-lb or Nm, low-range accuracy)
Ratchet to match your sockets
10 mm socket (air-side foot nut)
15 mm socket (damper-side foot nut)
2 mm hex (rebound knob set screw, if applicable)
Soft-face mallet (to dislodge the foot studs)
DH tire lever for seals
Isopropyl alcohol + lint-free rags
Nitrile gloves
A drain pan

Fluids

Exact oil types/volumes depend on model year; to check your fork’s specific information type in it’s serial number(typically located on the back side of the crown) at https://tech.ridefox.com/bike

Damper-side bath will use the bottle labeled 4wt oil
Spring side will utilize the bottle labeled Lower Leg Oil

*If you’re also opening the air spring (not required for this lower-leg only service), NA2 air chambers commonly use 3 cc Lower Leg Oil in the air chamber. Verify for your fork again in the Fox Tech Help Center.

Pre-service setup

Note your settings. Record rebound and compression clicks and air pressure.
Deflate the fork. Remove air cap and release pressure slowly to help prevent suck down
Remove wheel & brake caliper. Secure the caliper so it does not damage the frame
Remove fender and brake hose guide
Remove fork from bike. This part is not necessary but we feel makes the process simpler. For help with removing and installing the fork check out our blog here.

Step-by-step procedure

1) Loosen the foot nuts

Position the fork horizontally at an angle in which the lowers are slightly higher than the crown (keeps oil from running up the legs).
Damper side: loosen the 15 mm foot nut a few turns (leave it on the threads).
Air side: loosen the 10 mm foot nut a few turns (leave it on).

2) Free the shafts(do this over the drain pan)

With both nuts loosened but still engaged at least 3 full turns, hold the respective socket on to the nuts and LIGHTLY strike each of them with a soft mallet to unseat the foot studs from inside the lowers. Remove the nuts and crush washers; catch any oil.

3) Slide off the lowers

Gently pull the lowers straight down and off the stanchions. Drain the old bath oil into a pan. Inspect for metal/shiny debris.

If you find any metal or shiny debris you should look further into it and contact our shop to get a professional opinion.

4) Remove & prep wipers/foam rings

Pry out dust wipers carefully (DH tire lever, be gentle to avoid damaging the lowers). Insert the tire lever under the bottom of the wiper and pry upwards.
Remove foam rings.
Clean the inside and exterior of the lowers thoroughly.
Soak new foam rings in the ‘Lower Leg Oil’ before installation.

5) Install new wipers

With the wipers dry(no grease or oil), press new wipers squarely into the lowers with the seal driver. Confirm they’re fully seated and even. They should sit flush against the surface of the lowers.
After the wipers are installed grease the inner surface with a thin layer of suspension grease.
Insert the new oil soaked foam rings into the groove beneath the wipers.

6) Refit lowers part-way

Slide the lowers on just far enough that the shaft ends appear in the dropout holes. Slightly offset the lowers allowing you to focus on one wiper at a time. It will take some wiggling in a circular motion to pass the stanchion through the wipers.
Once onto the stanchions the lowers should slide freely to little or no friction. If there is friction the foam ring may have gotten pinched between the lowers and stanchion. To fix this you will need to remove the lowers and try again.

7) Add bath oil (measured)

With the fork still inverted/level, use syringes to add. For fork volumes visit https://tech.ridefox.com/bike and type in your fork’s serial number.(Serial number can be found on the back of the crown):

Air-side bath: Lower Leg Oil
Damper-side bath: 4wt Oil

8) Seat lowers & install crush washers + nuts

Slide the lowers all the way on until the foot studs protrude from the bottom of the lowers.
Wipe away any excess oil on the bottom of the lowers and foot studs.
Fit new crush washers and thread on the foot nuts by hand.

9) Torque the foot nuts (do not over-tighten)

Torque specs for your specific fork can be found on the same page as the oil volumes.

10) Reinstall rebound knob, brake, wheel, and axle

Refit the rebound knob (ensure the rebound knob spins freely).
Reinstall caliper and rotor (torque per brake maker).
Install axle; for KaboltX, tighten pinch bolt to 5.1 Nm (45 in-lb) after seating the lowers.

11) Re-pressurize & function check

Now is a great time to reset your SAG

For help with this process check our blog post on setting SAG

Cycle the fork 10–15 times through ~30–50 mm travel to distribute oil and purge air.
Wipe away any excess oil around the wipers.
Reset rebound/LSC/HSC to your notes and test ride.

Back to News