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: 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: 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: 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: 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: 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.