Fox Fit Damper Oil Change
After five years or so the fit4 cartridge damper in my 2017 fox34 (id C8sb) was quite sluggish. This is to be expected as the bladder ingests oil over time.
The damper cartridge is easy to remove with a socket or just a large adjustable wrench. The tricky part is removing the valve at the top in order to drain the old oil and refill. I was following the official fox fit4 damper guide. I was expecting a steel ball at the bottom of this valve as shown in the damper rebuild guide. There was none. I neglected to see there was a steel ball detent on the side of the valve. This ball provides nice clicks while you rotate the low speed compression knob. The valve is held on by a steel circlip who’s diminutive size belies its ability to fly to the farthest reaches of any room while you attempt to remove it. In the end I lost both the circlip and the ball, and after many enjoyable hours searching only found the circlip. The detent ball is not necessary.
Top of the damper assembly where the valve sits
low speed compression knob, circlip, and valve
damper bladder clearly pretty fat. Too fat to even fit in the stanchion with the damper rod pushed in all the way
Officially fox recommends their Fox R3 5w oil for the fit damper, but any oil with close cST (centistoke) rating can be used effectively. A quote on mtbr suggests Fox R3 5w oil is subpar in cold:
…it thickens up worse in the cold than any other fluid I have tested. At 0C it’s about 7x thicker.
Pretty much any other brand of 15 cSt fork oil will do better at ambient and cold temps. I’d suggest Motorex 2.5wt (14.5 cSt @ 40C) which is 30% thinner at 0C.
The other tricky part of the process after refilling with new oil is bleeding the air out. Helps to vaccuum the oil in a syringe and pour slowly to avoid bubbles. Official fox guide recommends filling from bottom. This may make it a lot easier to avoid bubbles, but is not necessary. A mixmizer syringe is very useful to pour the oil in. This youtube video is helpful: https://www.youtube.com/watch?v=paQtjVv7jnU.
Useful links about different types of oil and oil ratings:
- http://www.peterverdone.com/wiki/index.php?title=Suspension_Fluid
- http://www.peterverdone.com/suspension-fluids/
- https://www.shockcraft.co.nz/technical-support/suspension-oils/fork-oil-selection-charts/fox-oils (useful information for other forks as well)
- https://transmoto.com.au/comparative-oil-weights-table/
Other useful links
Comments
You could be the first to comment.
Say something
Thank you
Your comment has been submitted, it will take a few minutes to show up.
Return to page
OOPS!
Your comment has not been submitted. Either you messed up, or the comments are broken, sorry.
Return to page