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Day: July 31, 2013

FOX Racing Shox F29 O/C CTD Oil Replacement

Published July 31, 2013

My primary XC bike, a 2013 Salsa El Mariachi Ti, came fitted with what was listed as a Fox F29 CTD, Tapered, 15mm Thru Axle, 100mm fork. I was warned that newer FOX forks need oil replacements fairly frequently, so after long rides this spring I figured I should do some work on it, unlike my F29 RLC which I let go for years. Unlike the F29 RLC which I’d done previously, FOX doesn’t publish oil the replacement procedure on their consumer FOXHelp site, so I had to do a bit of digging to find a process that worked for me.

Having a sealed cartridge damper, and based on the recommendation from a helpful tech that I spoke to at FOX I decided that I’d leave the damper alone and just replace the oil in the lowers. Since it’s sealed there shouldn’t be any contamination, meaning that the oil in here doesn’t need to be changed nearly as often as in the rest of the fork. In the end I basically followed the F29 RLC/RL procedure, but because of the cartridge damper I had to put the oil in the bottom of the fork leg, which was a little tricky, but worked well in the end.

Here’s the rough process I followed which does not change the oil in the damper. By first understanding the F29 RLC/RL steps then looking over the O/C CTD design this becomes pretty obvious, and seems to worked out well. The major variance is steps 20-24, as previously oil would be added to the top of the damper before fitting the top cap and in these steps it is added through the bottom of the leg:

  1. Remove the fork from the bike.
  2. Write down the current fork rebound and pressure settings for easier setup next time.
  3. Remove screw from center of CTD selector. Put the lever in the Trail setting and hold it in place while removing the screw (don’t allow it to press hard against the stops).
  4. Remove the rebound knob from the bottom of the damper leg.
  5. Unscrew the nut from the bottom of the damper leg until it is flush end of the selector, tap with a dead blow hammer until it pops loose.
  6. Unscrew the top damper leg cap, lift the damper out. Drain oil from the leg and stanchion, wipe down outside of damper. Set damper aside.
  7. Unscrew the air chamber fill cap. Put a rag over the Schrader valve to catch spray and let all the air out.
  8. As in Step 4, unscrew the nut from the bottom and tap to free things up.
  9. Remove the top cap from the air chamber leg, remove and set aside.
  10. Pull the uppers and lowers apart.
  11. Push the air spring out of the upper. Wipe down parts, set aside.
  12. Replace wipers and foam rings if desired. For this oil change I did not swap the seals as they looked good, but I did clean and re-oil the foam rings. These can easily be removed with tweezers.
  13. Grease the threads at the top of the air chamber with Slick Honey.
  14. Push the air spring back into the air chamber upper from the top. Ensure that the threaded bit sticks out the bottom.
  15. Put the uppers and lowers back together. Push them together far enough so that the threaded end of the air spring is visible through the hole in the lower, but not seated.
  16. Pour the appropriate amount of oil (see the Oil Volumes chart) for the spring-side oil bath into hole. For the 2013 32 Float 29″ 80-100 (O/C CTD damper) fork this is 30 mL.
  17. Push the air spring in further and compress the fork to push the threaded rod out the hole. Put the crush washer and nut back on the bottom of the fork leg. Torque to 50 in-lb.
  18. Pour 5 mL of Float Fluid (one packet) into the upper part of the air chamber.
  19. Put the air chamber top cap back on, torque to 220 in-lb.
  20. Grease the threads at the top of the damper side and reinstall the damper, torquing to 220 in-lb.
  21. Oil now needs to be added into the hole at the bottom of the damper side, as it was on the spring side. Manually compress the fork slightly to push the rod from the damper in and provide space for the oil to flow.
  22. Pour the appropriate of oil for the damper-side oil bath into the hole. For the 2013 32 Float 29″ 80-100 (O/C CTD damper) fork this is 30 mL.
  23. Manually compress the fork so the threaded rod on the bottom of the damper is sticking out of the hole. Be careful not to spill any oil.
  24. Put the crush washer and nut back on the bottom of the fork leg, torque to 50 in-lb.
  25. Add the appropriate amount of air to the air chamber. Wipe down the fork and check for leaks.
  26. Reinstall the fork and set it back up. You’re done.

The following two drawings show the CTD VCT damper, which helps explain how the damper side of the fork is put together. Note that there are two types of the CTD damper which may be found in this fork: the original one and the VCT version. According to FOX the VCT damper can be identified by vent holes around the top, as seen in these images:

The variant of the damper does not matter for the aforementioned procedure, but if the damper oil is to be replaced then this changes the amount of oil needed. The non-VCT damper uses 74 mL while the VCT damper uses 69 mL. I found out about this when I called FOX to ask about the disparity between the damper oil volume on the Oil Volumes chart and the Subassemblies image. I was told that the Oil Volumes chart was likely made off of the original version of the damper and the VCT damper (which is identifiable by the vent holes) volumes are as shown on the drawing.

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