ROTOSHIM Shock Absorber Ford Model A (1928 - 1931)

The ROTOSHIM damper (lever arm shock absorber) design uses the essential elements of telescopic dampers; steel shim stacks control the fluid flow and pressurised oil prevents cavitation. These elements combine to allow the dampers to be tuned to give the correct level of damping for the vehicle weight and spring stiffness. The dampers are supplied pre-set and require no adjustment, just bolt on and drive. Damper bodies are manufactured from aluminium, while the rotors are from high tensile steel. The seal at the rotor is a UK manufactured, energised PTFE composite. The rotor is supported on bronze bushes. Both the rotor and housing are machined to very close tolerances, requiring no internal seals. Each unit is assembled by hand, filled with oil on our own vacuum filling rig to eliminate air bubbles and tested before packing. The aluminium body and cap are anodised to MIL-A-8625 and the rotor is coated with manganese phosphate giving long lasting corrosion protection.

ROTOSHIM dampers have no air space.
The damper is pressurised using our own proprietary mechanism which allows for the expansion and contraction of the oil with temperature. The internal design of the damper is arranged to generate damping force only by pushing oil through the valve at positive pressure, never drawing through at negative pressure.

ROTOSHIM dampers are not provided with an adjuster. The original dampers operate by forcing thick oil through a hole. This gives a "square law" damping rate and can be very unpredictable, depending heavily on the oil temperature. ROTOSHIM damper valves give something much closer to the ideal "linear" damping rate and are less sensitive to oil temperature. ROTOSHIM dampers do not need an adjuster to correct for these issues.

Durability testing has been carried out in two stages on the ROTOSHIM. For the first stage test dampers were fitted to a machine which actuated it through its full travel in both directions, 3 times a second for 40 hours. This is the equivalent of driving down the stairs for 40 hours or a lifetime of pot holes.  The second stage a set of dampers were fitted to a car that covered thousands of road miles, raced at Pendine Sands exposing them to salt water and driven in anger up Prescott Hill. After each stage, the dampers where dismantled, dimensionally inspected for wear and checked for seal damage. At no point did the original seals require replacement nor did the lever arm shock absorber suffer any measurable wear or damage.

All ROTOSHIM lever arm shock absorbers are made by us in the UK and undergo full dimensional quality control with calibrated equipment before assembly. Dampers are checked after assembly for function and oil leaks. All materials are sourced from reputable mills and are supplied with full certification. All anodising and coating treatments are processed in the UK and are certificated to meet industry specs. The seals are UK manufactured, quality controlled by us and certified to meet industry specs.