In the last post, I updated the spring and bottoming function in the Boxxer on my DH bike. I rode it after and it was very much improved. Now, I’ve be swapped out the damping fluid and lubing the seals.
OEM production rarely provides very good seal lubrication. Lubing the seals with the right lube can make a huge difference in many forks. Taking this fork apart to lube the seals is important. The dust seal had some reasonable lube but the oil seals did not. I fixed that and it made some difference.
I lubricated the fork with Dow Corning MOLYKOTE® 33 EXTREME LOW TEMP. BEARING GREASE, LIGHT.
The damping fluid and oil height was also checked.
Oil height compressed: 100mm (lots of internal air spring resistance.)
Oil height extended: 185mm (initial and after). 175mm spec.
Note in the image that the compression circuit won’t allow for an oil height much lower than 185mm regardless of desire.
Rock Shox uses Maxima 85-150 Fork Fluid for damping on most forks. An ISO viscosity of 15.9 (cSt@40). This is very good as any good cartridge fork in serious motorcycle cartridge forks are designed around an ISO16 viscosity. I use Red Line fluid in my suspension. It’s just the best you can use and makes a dramatic difference in my forks functioning. To match the ISO16, mixing Red Line works out to 20.8% Extra Light, Blue and 79.2% Light, Yellow.
I matched the initial production viscosity to set a baseline with my tune from the OEM. I can mix different fluid later as need be.
In riding the fork on this past outing with these changes, it’s pretty dialed. As I’ve said before, though, I’m recovering from a wrist injury and riding very rear heavy on the bike. Even during this weekend, I started adding some more compression damping to the fork to hold it up and this was due to how my wrist was feeling and how my riding was chainging. Tuning suspension with such a moving target is tough but it’s better to be close than way off the mark. I’ve got a few weeks off of downhill so I’ll be seeing how things change next time.
