Here is the tight tolerance honed interior of the Feal shock tube. With tolerances controlled, shaft play is minimized and fluid blowby around the piston is kept consistent for an equal amount of damping from shock to shock. The Feal shocks are monotube, meaning that they use one main tube for the body with all the damping being done by the piston.
What you see at the bottom is a gas separator piston which keeps the shocks fluid separated from the high-pressure Nitrogen gas that reduces cavitation and foaming in the shock that can cause inconsistent damping. Pressurization reduces cavitation and foaming by raising the boiling point of the shock's fluid, just like how a pressure cooker raises the boiling point of water to speed cooking.
There must be some gas volume in every damper to make room for the fluid displaced by the shock shaft as the shock compresses. If there wasn't any gas, and if the shock was filled to the brim with fluid, the shock would just be hydraulically locked and not move!
The Feal piston is casted, then machined to closely control the tolerances. Most shocks in the mid to low price range simply use the pistons as cast, but Feal goes the extra step to assure close tolerances between the piston and the Christmas tree.
The holes in the Feal piston are shaped to facilitate a digressive damping curve. A digressive curve means that the shock can have a lot of low piston speed damping force yet blow off at higher speeds. A digressive curve gives a lot of body motion control in roll and pitch like a stiff shock but can blow off at higher velocities giving a good ride and good traction.
The many different shims used in the christmas trees for our build are laid out in the order they are to be assembled according to the build sheet. How the christmas tree is put together is critical for the shocks' correct performance.
The piston shaft assembly is started by removing the piston and putting the compression christmas tree together.
Odi is measuring the christmas tree's stopper washer. This is a thick shim that limits the christmas tree's deflection. Its diameter controls a lot of the high-speed damping.
The shaft has two nuts, the top one keeps the camber plate and spring seat on the shaft while the capped bottom nut hold the piston to the shaft and blocks the hole in the shaft that the adjuster rod goes through, preventing fluid from going through the shaft and blowing out the top of the shock by the adjuster knob!