Though there are many types of
sealing arrangements, there are five main basic parts or elements in a
seal system: a dust seal, a stopper ring, an oil seal, a backup ring and
a slider bushing. Each performs a specific function.
- Dust Seal System: It consists of a simple
rubber or plastic ''grommet'' at the place where the two halves of
shock assembly come together. Its main purpose is to keep dirt and
debris away from reaching the actual oil seal.
- Stopper Ring Seal System: Usually, a stopper
ring is a ring of steel spring wire or a large C-clip which is
fitted in a machined groove in the shock housing below the dust
seal. Its purpose is to keep the seal below it from being forced
upward and out of position by the force of the springs during shock
compression.
- Oil Seal System: The oil seal lies below the
stopper ring. Usually, they are made of steel with a rubber cover.
It is usually pressed or ''hammered'' into its seat in the housing
by a specially-fit driver. Its main purpose is to keep the fluid
inside from leaking out and to keep the dirt out.
- Back-up Ring Seal System: The back-up ring is
below the oil seal. It looks like a big washer. The main functions
of the back-up ring are to abate the upward forces against the seal
and make them to spread evenly over the sealing surface. It also
protects the seal from the slider bushing being driven too far up
the tube and into the rubber parts.
- Slider Bushing Seal System: The slider bushing
is a sort of ''tilted pad'' bearing. It creates a compression zone
from where the oil can form a low-friction film between the shock
tube and the housing. It is usually made of brass.