Monroe's Technical Support will help you find
answers to the most frequently asked product and installation questions
and provide invaluable technical training information. If you need
additional information or assistance, Monroe's Ride Control Technical
Assistance Team can assist you.
STRUTS
WHAT IS A STRUT
Now that we have a more thorough understanding of shock design, let's
focus on the strut. The strut is a common damper type used on many of
today's independent suspension, front wheel drive vehicles as well as
some rear wheel drive vehicles.
A strut is a major structural part of a suspension. It takes the place
of the upper control arm and upper ball joint used in conventional
suspensions. Because of its design, a strut is lighter and takes up less
space than the shock absorbers in conventional suspension systems.
Struts perform two main jobs. First, struts perform a damping function
like shock absorbers. Internally, a strut is similar to a shock
absorber. A piston is attached to the end of the piston rod and works
against hydraulic fluid to control spring and suspension movement. Just
like shock absorbers, the valving generates resistance to forces created
by the up and down motion of the suspension. Also like shock absorbers,
a strut is velocity sensitive, meaning that it is valved so that the
amount of resistance can increase or decrease depending on how fast the
suspension moves.
Struts also perform a second job. Unlike shock absorbers, struts provide
structural support for the vehicle suspension, support the spring, and
hold the tire in an aligned position. Additionally, they bear much of
the side load placed on the vehicle's suspension. As a result, struts
affect riding comfort and handling as well as vehicle control, braking,
steering, wheel alignment and wear on other suspension
STRUT COMPONENTS
Typically, struts consists of a
coil spring to support the vehicle's weight, a
strut housing to provide rigid structural support for the assembly, and a
damping unit
within the strut housing to control spring and suspension movement.
The bottom of the strut body attaches to the steering knuckle, which in
turn connects to a lower control arm through a lower ball joint.
The top of the strut is connected to the vehicle body through the
upper strut mount, in some cases called a
bearing plate.
This bearing plate allows the strut to pivot as the wheels are turned.
It must be flexible enough to handle slight angle changes and dampen
movement of the upper end of the strut. This mount or bearing plate
transfers vehicle load to the strut and spring, making the upper
mount/bearing plate the load carrier and the lower ball joint the
follower.
The
strut housing holds
the damping unit and fluid. It is made of heavy gauge steel so that it
is rigid enough to provide structural support and withstand road shock.
The
piston rod of the
strut is much larger in diameter than the piston rod of the typical
shock absorber. This is to withstand the side load on the strut shaft. A
strut rod will measure up to 7/8 of an inch in diameter while the
piston rod of a typical shock measures up to ½ of an inch in diameter.
A
coil spring is located
between the upper and lower spring seats. It is held there by tension.
The lower spring seat is welded to the strut housing, while the upper
spring seat is kept in place by the upper strut mount.
Struts also have a
jounce (or compression)
bumper
located under the upper spring seat. The purpose of this component is
to limit suspension travel by not allowing suspension components to hit
together.
Finally, a large nut at the end of the strut rod holds everything together.
