Bypass Reservoir Shock Rebuild by Fox Factory - Shock RebuildingPosted in How To on April 30, 2013
We recently visited the FOX Factory shock service department in El Cajon, California, where the company builds and services many of its performance off-road shocks. The dedicated crew here builds to custom order and offers revalve and rebuild service to customers ranging from weekend warriors to the top race teams.
We wanted to take a look at what lies inside a typical reservoir shock and the steps needed to tear one down and get it back together. FOX recommends racers rebuild shocks after each race and non-racers rebuild about once a season for optimal performance.
The internals of a reservoir shock used on a coilover and the main body internals used for a bypass shock are the same. A coilover has a coil spring over its exterior and can provide the means to support the vehicle at ride height. A bypass shock is used in tandem with a coilover shock or other suspension spring and serves only as a suspension damper. It utilizes some number of oil bypass passages that allow the shock to provide different damping rates over its range of shock travel to improve how the suspension reacts to small and large obstacles.
The main shock has a damping piston with valve stacks on both sides. One stack controls the compression rate and the other stack controls the rebound rate. Additionally, these shocks use a piggyback or remote reservoir to house additional shock fluid and an internal floating piston (IFP) that separates the shock oil from a volume of high-pressure nitrogen gas. The nitrogen serves to prevent air bubbles, or cavitation, from occurring in the shock oil.
Joe Moore at FOX took us through the teardown, inspection, and rebuild of a bypass shock to show us what all is involved and pointed out a few tips along the way. FOX offers a concise text manual for this rebuild. Our photos here should help you further understand the various parts teardown and assembly during the process.
What’s a Bypass Shock?
A bypass shock has externally mounted bypass tubes that allow shock oil to travel around the internal piston during certain ranges of the shock travel. In this way, the shock-damping rate can be position-sensitive. It offers lighter damping during initial travel from ride height (most bypasses active) and greater damping as more travel is used (fewer or no bypasses active).
There are some added steps to the rebuild if you’re dealing with a bypass shock. In this case, the shock had one compression and one rebound bypass assembly that needed to be cleaned and rebuilt.