FOX 981-35-403-R Factory Race 3.5x18 External Bypass 5-Tube Piggyback Shock (R)

Application / Fitment Notes

• Universal - the FOX 981-35-403-R is an off-the-shelf Factory Race Series external bypass shock for custom suspension fabrication, Baja-class trucks, unlimited-class off-road race vehicles, long-travel prerunners, Class 10 and Class 1 buggies, sand rails, and any high-travel off-road racing application. It is not a direct bolt-on replacement for any specific production vehicle - the builder mounts and configures it to their chassis.
• Right-hand orientation (-R): On a bypass shock, the -R designates the right-side shock, whose tube and reservoir layout mirrors the -L. When viewed from the top of the shock with the reservoir closest to you, compression tubes are always on the outside edges and rebound tubes on the inside. Match orientation to your chassis fabrication. The companion left-hand shock is FOX 981-35-403-L.
• Standard off-the-shelf valving: 3,2 Compression / 70 Rebound. For race applications, custom valving tuned to vehicle weight, spring rate, full suspension travel, and intended terrain is strongly recommended - AccuTune Off-Road and other authorized FOX tuners offer valving services for the 981-35-403 series. The off-the-shelf valving is a starting point, not an optimized race tune.
• Bypass tube layout: standard off-the-shelf. Custom tube layouts (repositioning tubes for frame rail, link, or chassis clearance) are available from FOX directly or through authorized dealers for applications where the standard layout creates interference.
• The 3.5" x 18" stroke makes this shock appropriate for the longest-travel applications in the Factory Race Series 3.5" lineup. Verify extended and collapsed lengths against your chassis mounting points and available bump and droop travel before ordering.
• Rotating body cap allows the bypass tubes and piggyback reservoir to be repositioned around the shock body after installation without disassembly for clearance adjustment.
• Sold individually - one shock per order. A full axle pair requires one 981-35-403-R and one 981-35-403-L.

Features

• 5-tube external bypass - 3 compression tubes + 2 rebound tubes. The 5-tube configuration is the most refined position-sensitive damping arrangement in the off-the-shelf FOX Factory Race Series 3.5" piggyback lineup, providing three independently adjustable compression zones and two independently adjustable rebound zones across the shock's 18" of travel. Each tube's adjuster opens or restricts oil flow through that circuit at its defined position in the stroke, allowing the damping curve to be shaped with zone-by-zone precision: soft early compression for compliance over rocks and whoops, firmer mid-stroke for body control, and a progressive final zone for bottom-out resistance - independently tunable for rebound in the same zone structure.
• 3/4" bypass adjuster tubes - the 3/4" tube diameter is FOX's standard for the 3.5" factory race series 5-tube configuration, providing appropriate oil flow capacity for the 3.5" body's oil volume and the 18" stroke's damping demands. Each adjuster uses a clicker mechanism for repeatable field adjustment without tools, with black anodized housings and color-coded seals for immediate visual identification: blue for compression, red for rebound, gold for valves.
• 18" stroke - at 46.450" extended and 28.450" collapsed, the 981-35-403 is a long-travel racing shock. 18" of wheel travel (at a 1:1 motion ratio) places this shock firmly in unlimited prerunner, Class 1 buggy, and Baja 1000-class territory where suspension compliance over high-speed desert terrain at sustained velocity is the primary design requirement. Most street-truck and moderate off-road builds use significantly less travel.
• 3.5" body diameter - the largest of FOX's aluminum-bodied factory race bypass piggyback options (above the 2.5" and 3.0" body sizes), providing the greatest oil volume for heat capacity, the most damping force capacity, and the greatest resistance to fade under sustained desert racing conditions. The 3.5" body is the choice for heavy vehicles, maximum travel applications, and races where sustained high-speed off-road use over many hours generates heat loads that smaller body shocks cannot manage without fade.
• FOX Grey Cerakote® dual coat body finish - proprietary ceramic coating applied over a zinc plated basecoat for corrosion resistance and surface hardness that exceeds standard anodized or painted finishes. The same coating technology used in aerospace and firearms applications.
• 1" shaft diameter - the 3.5" body platform uses a 1" diameter shaft, providing maximum resistance to bending and deflection under the lateral loads generated by extreme-travel suspension articulation at high speed. Hard chrome plating or equivalent surface treatment extends seal life and resists scoring from abrasive debris.
• Viton seals - Viton (fluoroelastomer) sealing material delivers low friction, low wear, and high temperature resistance beyond what standard nitrile or polyurethane seals provide. In sustained desert racing use where shock oil temperatures rise significantly during high-speed desert stages, Viton seals maintain their sealing effectiveness and dimensional stability where lower-grade materials would harden, crack, or extrude. The redundant sealing pack (main, wiper, scraper) provides multiple independent barriers against oil loss and contamination ingress.
• 3.0" x 16" piggyback reservoir - larger than the 2.5" x 10" reservoir on the 2.5" body shocks, the 3.0" x 16" reservoir provides substantially more supplemental oil and nitrogen volume. Additional oil volume slows the rate of temperature rise during sustained high-speed off-road use, extending the time before heat-induced damping fade affects shock performance during long race stages.
• PTFE-lined heat-treated alloy steel spherical bearings - low-friction bearing articulation with high wear resistance, essential for the aggressive suspension geometries and articulation angles encountered in long-travel racing applications.
• Rotating body cap - the bypass tubes and piggyback reservoir can be rotated around the shock body after chassis installation for clearance adjustment, eliminating the need to disassemble the shock to reposition routing.
• Fully rebuildable and serviceable - seals, piston assemblies, bypass tube components, and valving shims are serviceable by FOX-authorized service centers. Custom valving changes can be made at service intervals to refine the shock's performance as vehicle weight, spring rates, or intended terrain changes.

Specifications

• Part Number: 981-35-403-R
• Series: FOX Factory Race Series
• Type: External Bypass Piggyback Shock - Right
• Body Diameter: 3.5"
• Stroke / Travel: 18.0"
• Extended Length: 46.450"
• Collapsed Length: 28.450"
• Bypass Configuration: 5-tube (3 compression + 2 rebound)
• Bypass Tube Diameter: 3/4"
• Adjusters: 3 compression (blue) + 2 rebound (red)
• Standard Valving: 3,2 Compression / 70 Rebound (custom available)
• Reservoir: 3.0" x 16" piggyback
• Shaft Diameter: 1"
• Body Finish: FOX Grey Cerakote® over zinc plated basecoat
• Seals: Viton; redundant pack - main, wiper, scraper
• Bearings: PTFE-lined heat-treated alloy steel spherical
• Adjuster Housings: Black anodized, color-coded seals
• Mounting Width (between tabs): 1.50"
• Mounting Bolt: 5/8"
• Orientation: Right (-R)
• Rotating Body Cap: Yes
• Rebuildable: Yes
• Warranty: FOX motorsports product warranty (1 year, original retail purchaser)

Included Components

• 1x FOX 981-35-403-R Factory Race 3.5 x 18 External Bypass 5-Tube Piggyback Shock (Right)

Product Description

The FOX 981-35-403-R is the Factory Race Series 3.5" x 18" external bypass piggyback shock in right-hand configuration - the longest-stroke, largest-body off-the-shelf 3.5" piggyback in the FOX Factory Race Series external bypass lineup. At 18" of stroke, 46.450" extended, and 28.450" collapsed, this is a shock built for unlimited prerunner trucks, Class 1 buggies, long-travel race vehicles, and any application where 18" of suspension travel is required for competitive desert racing performance. The 5-tube bypass circuit - three compression and two rebound tubes, each with a 3/4" adjuster - provides the most refined position-sensitive damping tuning available in the off-the-shelf FOX 3.5" piggyback range, giving the builder five independent adjustment points across the stroke's compression and rebound damping curves.

The 3.5" body is the largest aluminum body in FOX's factory race bypass piggyback lineup, and the step up from the 2.5" and 3.0" body sizes is meaningful in sustained desert racing use: greater oil volume means a higher heat capacity ceiling before fade onset, more damping force capacity for heavier race vehicles, and more thermal stability over the long Baja stages and high-speed desert miles where smaller-body shocks begin losing damping consistency. The 3.0" x 16" piggyback reservoir adds significant additional oil and nitrogen volume on top of the main body's capacity. Viton seals - rather than the standard nitrile or polyurethane used in lower-tier shocks - maintain their sealing integrity and dimensional stability at elevated temperatures, which are a practical reality in sustained desert racing use. The redundant three-stage sealing pack (main, wiper, scraper) provides multiple independent containment layers against oil loss and contamination ingress from the sand, dirt, and debris that are constant companions in race environments.

Off-the-shelf valving is 3,2 Compression / 70 Rebound - FOX's standard base tune. Custom valving by an authorized tuner is strongly recommended for race applications: AccuTune Off-Road and other FOX bypass shock specialists offer the 981-35-403 with tuning services included, and optimized damping for the specific vehicle's weight, spring rate, and terrain will extract substantially more performance than the base valving provides. Custom bypass tube layouts are available for chassis configurations where the standard tube placement creates interference. The 981-35-403-R is sold as a single shock; the companion left-hand unit is 981-35-403-L.