Fox 36 Damper Mods
Updated 09-14-2024
My trail bike has a MY2020 Fox 36 170mm travel suspension fork with "Grip" damper. The design of the compression assembly is odd for the long travel application. Where I live now means I am riding my downhill bike less, so the poor performance is more annoying
Baseline Design
The existing base-valve design uses a threaded adjuster to change preload or even float on a stack of steel shims. The maximum amount of preload is controlled by a step on the piston measured as -0.29mm. The maximum float/bleed is controlled only by clearances and is measured as +0.73mm. The adjuster screw is a M5x0.8 thread so almost one full turn goes from effectively a large open orifice to a preloaded shim stack. This works very well for XC racing where you want a quick lockout, but that is not desirable when you want fine damping adjustments.
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| (a) Baseline: Adjuster Fully Open | (b) Baseline: Adjuster Fully Closed |
My goal is to convert the damper to be more like Fox's older RC2 dampers or the more recently released Grip X. I would like easy external adjustment of bleed and an internally adjustable shim stack.
Modifications to existing components for low speed bleed adjustment and shim stack
With a few small re-works and new parts
The valving pressure drop vs flow characteristic can be adjusted by
- Changing the needle profile or position of the needle in the seat
- Changing shim stack stiffness
- Changing shim stack clamp diameter (currently 8mm)
- Changing oil viscosity
Machining Drawings
Photos of machined parts
I made some modifications based on the scrap stock I had on hand