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Fox has two Propedal devices, the diagram shows
a propedal bolt which is a basic check valve design, the
bolt mounts into a hollow shock shaft to retain the main damping
piston and acts as the rebound needle
seat. The diagram shows the check valve, spring and
grub screw removed from the bolt, the black area on the bolt
represents an oil port. The lower sketch shows the check valve,
spring and grub screw installed in a cut away view of the bolt, the opened
entry of the bolt is the rebound needle seat.
The check valve inhibits oil flow on compression, forcing
oil through the shimmed piston and resulting in increased low speed
compression, by sacrificing small bump compliance rider induced movement
through the rear shock is partially eliminated. Rebound flow of oil going
the opposite direction passes through the check valve with little
obstruction other than the minimal spring pressure of the valve. Once
bicycle speed increases the check valve has little effect as volume of oil
and increased shaft speed force oil through the larger, shimmed damping
ports of the main piston.
 The icons on the left are the propedal settings
available in Float R's, ( printed on the air sleeve ) relevant to shim
configuration and dictated by the check valve during low speed
compression.
The Propedal bolt is standard equipment in Fox Van R,
Fox Vanilla R and Fox Float R, and is used to upgrade early Fox
Vanilla R, RC & Float shocks, although it is recommended to
de-tune the compression circuit on Vanilla RC's.
The diagram below shows a more complicated version of
propedal, situated at the base of the reservoir on the DHX 5.0 and 4.0
coil over, and 2005 - 2007 DHX Air, adjustable by means of an external
control knob, ( a 2 way lever on the 08 - 09 DHX Air ) with a non
adjustable version on the DHX 3.0 coil over.
A single shim ( green line ) covers six
return oil ports that are situated in the base of the
reservoir, backed by a large ( red ) tension
spring, the closed shim prevents oil flow to the
reservoir at low speed and diverts the fluid around the neck of
the ( blue ) position sensitive valve. The valve regulates oil flow
into the reservoir chamber via a central  stepped orifice (
static, this orifice is closed due to reservoir air
pressure ) and low speed compression resistants
is determined by adjustment of the propedal knob. The valve is not
fixed, although restricted in movement, and is directly effected by
opposing forces of tension springs, reservoir air pressure and shock
shaft displacement, the overall effect resulting
in position sensitive valve characteristics.
Low speed compression is dictated by the valves
position, and tension of the ( black ) spring situated
behind propedal adjustment knob, turning the knob clockwise
( + ) decreases spring tension, and the opposing reservoir
air pressure forces the valve to minimize the orifice size
situated at the neck of the valve. During large impacts the valve shifts
position to allow a greater oil flow through the orifice, and ( due to the
design of the valve ) permits the increase of oil to cycle
back through all six return ports ( static, the valve
covers the entry of all but two of the six return ports....their exit
governed by the spring loaded ( green ) shim ) During medium
shock shaft speed the valve hovers until opposing pressure dictates its
position, propedal effects are overcome by the increase
in the rapid cycle of the shock shaft as speed increases,
and the shimmed damping piston in the main body of the shock contribute to
overall damping with the aid of the position sensitive valve in the
reservoir.
Propedal, Boost Valve Adjustment and Air
Pressure in DHX Coil Overs.
Fox recommends 125 psi maximum in the boost valve of the
DHX 5.0, and 200 psi maximum in the DHX 4.0 and 3.0
The 5.0 can produce improvements with an
increase to 150 psi, and in some cases increasing the boost valve
pressure to 180 psi ( with the bottom out adjuster wound out
) had our test shock feeling particularly smooth and no signs of
transitional changes during compression or rebound. I urge common
sense when considering changes against the factory recommendations,
accuracy of shock pumps, rider weight, riding style, coil spring rates and
temperature should be some considerations.
Diagrams and an explantion on
the Float RP series to come | 
