Speed Sensitive Damper(SSD)
High/Low Speed FvAT/HSB Adjuster(RC4)
Modification Kit

High Speed FvAT/HSB Modification
(Floating Valving Assisted Threshold High Speed Blow-off )
Low Speed Adjuster Range Doubled (22 clicks)
Boost Valve Replacement or Removal


Replacement or removal of the boost valve depends on the style of linkage your bike has.

Build 1
If your frame's linkage is a regressive or falling rate linkage then you will need Build 1 to replace your boost valve
with our SSD speed sensitive valve to prevent square edged deep stroke harshness while maintaining bottoming resistance.

Build 2
If your frame has a progressive or rising rate linkage you will need Build 2 to remove of the boost valve and the high speed adjuster
will be modified to independently increase high speed damping and along with the linkage it will give you all the end stroke damping you will need.

Questions?? E-mail or call us and we can help you determine what your shock needs.

Build 1 (select this option in the cart)
For the linear and regressive linkages the High/low adjuster will be completely redesigned to create what we are calling a FvAT/HSB,
this will allow the rider to blend the low speed into the mid speed damping will maintaining pedal performance and low speed plushness.
RC2 will have the same internal modifications, but preset with our custom Transition tune.
The SSD valve will be required for this build to add bottoming resistance and to allow blow-off on square edged bumps as needed.

Build 2 (select this option in the cart)
For rising rate linkages the High/low adjuster will be completely redesigned to create what we are calling a FvAT/HSB,
this will allow the rider to blend the low speed into the mid speed damping will maintaining pedal performance and low speed plushness.
The RC2 will be preset with our custom high speed tune. No SSD valve will be needed.

The SSD valve will become an option only if needed for low rising rate systems and more aggressive free riding.

What will be done to your shock?

Stage 1 (included)
Removing the boost valve and replacing it with our Speed Sensitive Valving.
This fixes the middle to bottom of the stroke by removing the position sensitive portion and making it speed sensitive,
It still prevents bottoming and will now blow-off when needed on high speed square bumps, that the RC4/RC2 fails to do.

Stage 2 (included)
The main compression valving will be revalved and modified for the linkage system and type of riding.
The rebound valving will be revalved and set for the spring rate needed for the rider,
allowing the rebound adjuster to fine tune the low speed.
The stock RC4/RC2 valving is the same for all spring rates
and the low speed adjustment has to be compromised to compensate for the fixed high speed internal valving.
Stage 3 (included)
Seals, bushings, and dust scrapers will be changed to better quality and less friction.

Oil replaced with Spectro Suspension Fluid, Recharged with Nitrogen to reduce fade and heat affected pressure increases.

Options 1,2, and 3 (select this option in the cart)
Optional SSD valve(1) or shape factor anti-bottoming bumpers(2).

Details (included)
Includes custom revalve and setup for rider, frame leverage and conditions
and printed set-up chart. We will ask you all the right questions to help you help us with the best possible set-up.
Also includes complete rebuild service, new improved seals and dust wiper system, oil, nitrogen charge and typical wear parts* included in price

Stock DHX Bumper, Dust Seal and Oil Seal

*(Typical wear parts: shaft seal, dust scraper, shaft bushing, reducer DU bushings, and all internal o-rings)

The larger the reservoir the less pressure increase during full compression, this pressure effects the midstroke harshness for rising rate linkages.
Also the longer the run the hotter the shock gets, and with small reservoir volumes this could double the pressure in the shock at the beginning of the stroke and make it feel topped out or over preloaded.
Regressive linkages like the "Sunday" only benefit from the bottom-out original reservoir. Most frames will work with the standard reservoir.
High rising rate frames and aggressive extended downhill runs on linear and progressive linkages will benifit from the extended reservoir.

Cost $259 including the High/Low Speed FvAT/HSB Adjuster (RC4).
Cost $259 including the /Low Speed FvAT/HSB Adjuster (RC2).
Build 1 Optional SSD valve $49 , bumper $16.

Not available as a self install kit.

Damper Modifications apply to:




RC4 FvAT/HSB High/Low Speed Adjuster

SSD Valve



Speed Sensitive Damper (SSD)

FvAT/HSB/High/Low Speed Adjuster
(New High Speed Adjuster Piston and Blow-off System RC4)
(New High Speed Adjuster Piston and Preset Blow-off System RC2)

Modification Kit

Shock must be sent in to receive modifications.

Price $259

Download whats been done and set-up manual (27 MB)

Comparison Chart

options shown below

Order Here and Send Shock for Modifications

Choose the type of riding that you will be doing so we can custom valve it to your specific needs.

Click here for a description of our definitions

Type of Riding

Choose your shock model that the SSD kit will be installed in.

Shock Model

Choose rider weight.
Rider weight is without gear, we add 5-7 lbs for DH gear, 7-10 lbs for All-Mtn/Freeride.

Rider Weight

Choose the spring rate you will be using which gives you 30% sag.
We need this number to help set-up your shock rebound damping correctly.

Click here for sag setting Tips

Make sure that this spring gives you 30% sag with 2-3 turns of preload.
We will help you choose your correct spring if you are unable to.

Spring Rate

Choose your rider ability for us to set-up your shock.

Rider Ability

Provide us with Bike info to set-up your shock.




Provide us with any other info to help us set-up your shock.

Set-up Info



Can't figure out which build to order

Call or e-mail us

RC4 Build 1 Shown with SSD

What we've Done!




Modified Low Speed Adjuster with wider range - 22 click low speed adjuster (Stock 18 clicks)

FvAT/HSB-High speed adjustment - 12 Clicks(RC4)

FvAT/HSB-High speed Preset Custom Tune- (RC2)

Revalvable SSD Valve, High speed shims with custom tune, eliminate high speed harshness and dial in bottoming control.

Optional Shape Factor Bumper



Your shock will be better than new!

Complete Rebuild including all seals,o-rings and DU inserts replaced, Boost Valve and stock High speed valve replaced with High/Low Speed FvAT/HSB Adjuster.



Fox RC4/RC2

Only needed for Build Option 1
Sensitive Damper (SSD) Valve
adds more high speed compression control for regressive and linear linkages
Add option here
Price $49


Optional SSD Valve

Price $49




Shape Factor Bottom-Out Bumper

Progressive Bottoming Control

No more Tire Buzz or Harsh Bottoming

Click here for Technical Description


Option 2
Shape Factor Bottom-Out Bumper
Add option here
Price $24.95

Available Now


Optional Bumper

Price $24.95





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