BP-51 (BYPASS 51MM DIAMETER BORE) Shock Absorbers

The new BP-51 range of high performance, bypass shock absorbers is the result of an exhaustive development process aimed at delivering the ultimate in both comfort and control. Designed, developed and tested entirely in-house by ARB’s team of Old Man Emu ride engineers, BP-51 shock absorbers are vehicle-specific and utilize existing mounting locations to provide easy installation without the need for additional vehicle modification. Unlike most other adjustable shock absorbers, which provide adjustment for compression only, the BP-51 range allows on-vehicle, independent adjustability of both rebound and compression to offer class-leading ride customization that can be tailored to an individual vehicle or trip requirements.


Bypass Technology

In addition to the velocity sensitive damping used in most shock absorbers, where the faster the piston moves, the higher the level of damping is generated, BP-51 shock absorbers also generate damping dependent on the position of the piston within the shock absorber’s body via their bypass design. While most shock absorbers only generate damping based on fluid flowing through the piston, the BP-51 offers an alternative path from one chamber to the other, around the piston in the form of bypass passages. Some fluid flows through the piston and some fluid bypasses around the piston in the bypass passages. This results in an ability for the shock absorber to provide the best of both worlds, with a comfortable and compliant ride during normal driving and a more controlled ride over more challenging terrain. With greater levels of damping generated at each end of the stroke, the piston slows as it approaches full compression and extension, preventing harsh topping out against the bump stop and allowing larger bumps and corrugations to be absorbed more easily.



Spherical Bearings

Large, Teflon-lined spherical bearings.

Spherical Bearings

Large, Teflon-lined spherical bearings.


Quality oversized rubber bushings result in excellent longevity.

Shaft Guard

Replaceable, impact resistant, high-density polyethylene shaft guard prevents damage to the shock absorber shaft from stones and other debris.

Spring Seat

6061 grade aluminum spring seat.

Piston Shaft

Hard chromed, ground piston shaft for the ultimate in strength and durability.


External, independent rebound and compression adjustment allows fine tuning of ride comfort and control to suit varying vehicle and trip requirements.

X5K Coil

High-quality X5K grade steel coil, for use on coil over models, incorporates application-specific design.

Remote Reservoir

6061 grade aluminum remote oil canister allows for increased oil volume, resulting in lower oil temperatures.

Shock Absorber Body

51mm bore, 6061 grade aluminum shock absorber body with type III, hard anodized finish for increased heat dissipation and corrosion resistance.

Piggy Back Clamp

Remote reservoir piggy back clamp allows easy connection of the remote oil reservoir to the main shock absorber body.

Spring Adjustment

6061 grade aluminum adjustor allows adjustment of spring preload and ride height.

Top Hat

6061 grade aluminum top hat.

High Temperature Hose

Durable Dash 6 high-temperature Teflon hose incorporates high-flow fittings for optimum oil flow.

Development and Manufacturing

All BP-51 shock absorbers are manufactured in-house by ARB. In order to achieve this, significant investment has been made in state-of-the-art machining and hard anodising equipment, allowing ARB total control of the process to ensure the highest possible quality. BP-51 shock absorber bodies are manufactured using aircraft grade (6061) anodized aluminum to dissipate heat more efficiently than steel or alloy steel and provide superior corrosion resistance. Extensive lab, real world and destructive testing have been undertaken during the development process to ensure that reliability, longevity and performance all meet ARB’s impeccable standards.

Read the Y62 Patrol Development

    Bypass shock absorbers have been used in off road racing for many years and are renowned for their ability to handle the toughest terrain and endure through the harshest abuse.

    While most shock absorbers use velocity sensitive damping (meaning the faster the shock absorber compresses and expands, the higher the level of damping force is), bypass shock absorbers take this to the next level by also generating damping dependent on the position of the piston within the shock absorber body.

    Bypass refers to the ability of the hydraulic fluid to bypass the piston by being routed externally to the shock bore; creating a high level of comfort initially but increasing the damping forces as the shock reaches the end of its travel in both compression and rebound. In Old Man Emu BP-51 shock absorbers, the amount of bypass is adjustable so that it can be tailored to suit different terrain, speed and loads.



    Traditionally, the bypass shock design incorporates a number of tubes that run external of the shock absorber body in order for the hydraulic fluid to bypass the internal piston.

    This design has prevented bypass shocks from being incorporated into everyday vehicles without expensive modifications due to dimensional constraints; especially modern coil-over independent suspension. BP-51 uses a unique extruded alloy body where the tubes are replaced by passages within the shock absorber body, allowing it to fit into tighter confines such as inside a coil spring.


    While an Old Man Emu suspension system incorporating Nitrocharger shock absorbers is a vast improvement over standard suspension systems for both on and off road use, by design, there are always compromises between comfort and control.

    Old Man Emu’s BP-51 high-performance bypass shock absorbers bring the latest in racing bypass technology to everyday 4×4 drivers, giving the ability to customize their ride with user adjustable compression and rebound damping control while still being fully compatible with Old Man Emu springs and suspension related components.

    You don’t need to be competing in off road events to appreciate the benefits of adjusting your ride for optimal performance when faced with challenging terrain, towing or carrying loads, and returning to the asphalt with a compliant comfortable ride.


    Bypass 51mm diameter bore.


    All shock absorbers need some amount of airspace to allow the hydraulic fluid to expand and move properly, however, when the air mixes with the hydraulic fluid, it can cause it to aerate (foam) and therefore lose damping effectiveness. This most commonly happens in standard hydraulic shocks.

    Nitrogen gas is used to replace air within a shock absorber to help control the flow of hydraulic fluid (this is because it is not readily absorbed into the fluid like air). Various shock designs do this differently.

    Within a twin tube shock, the gas sits in the reserve tube to keep pressure against the fluid as it passes through the valving and prevents it from being dumped into the reserve tube.

    A monotube shock uses a floating piston at the base of the piston bore to separate the hydraulic fluid from the gas, also preventing aeration. This design, however, reduces the travel of the piston within the shock body, affecting the overall travel of the shock.

    Like a monotube shock, the external canister in a BP-51 utilizes a floating piston to separate the hydraulic fluid and gas, however, it is contained within an external reservoir so as not to cause a restriction on the shock travel. The reservoir is large to handle the increased fluid volume in the shock and is remote mounted to aid fitting. Additionally, it can also help cool the hydraulic fluid as it is routed away from the hotter moving internal components.


    Whilst many aftermarket bypass type shock absorbers are not tuned to suit a particular vehicle or spring, Old Man Emu’s ride control engineers have spent considerable time refining the BP-51s to not only be vehicle specific but also matched to Old Man Emu spring selections. Unlike when fitting Nitrocharger Sport shocks, which are specifically tuned to match the selected spring, BP-51’s valving is designed to allow a greater level of personal tuning to match vehicle load and track terrain; with recommended settings available in the fitting and user guides.

    Customers can use this as a starting point and then customize accordingly to suit their own personal comfort and driving style preferences.



    Damping refers to the slowing of the shock absorber’s oscillation. This is controlled by a series of valves that slow the movement of the hydraulic fluid through the piston. Valving controls the movement of the pistons during both the compression and rebound strokes.


    Adjusting the compression valving has an effect on how comfortable or firm the suspension is when the suspension of the vehicle compresses. Too firm and the vehicle will feel every bump and ripple in the road surface as the shock tries to prevent the spring from freely compressing. Too soft and the ride will become more comfortable, however, more body roll can be felt when tackling corners and the vehicle may nose dive during braking, resulting in less control. The suspension may also easily bottom out on the bump stops.

    Adjusting rebound valving effects the rate at which the shock allows the spring to return back to ride height once it has been compressed. Higher rate springs are used to maintain correct ride height when either accessories or greater constant loads are added to the vehicle. When these springs are compressed with greater load, the energy stored within the spring is also greater and requires extra damping control as it rebounds. Not enough rebound control may cause the shock absorber to top out, causing internal damage to the shock or allow the suspension to bounce numerous times after hitting an obstacle, resulting in less control of the vehicle.


    If you have fitted your vehicle out with accessories that add overall weight such as a bumper, winch, rear bar, long range fuel tank or drawer system, among others, the additional weight will have an effect on the ride and handling characteristics of the vehicle; resulting in the need for suspension with increased spring rates.

    While a tuned suspension where the shock absorber is matched to a spring rate will give greater comfort and control over a range of terrain types and load carrying requirements, these systems may offer a firmer ride than standard when unloaded (although giving better control).

    If your vehicle spends a lot of time unloaded, the ability to decrease compression and rebound damping can give greater comfort on road. Whereas the ability to increase compression and rebound damping can benefit you when carrying larger loads or driving off road at greater speeds.