Strut Assembly
Your vehicle’s suspension is what connects the wheel spindles to the body and
controls the ride over rough surfaces. There are two components that form most suspension
systems, springs and
shock absorbers.
Springs support the weight of the vehicle and are used to soften the impact that
bumps transfer to the vehicle while driving. Shock absorbers control the bump and
rebound that occurs when the sprung vehicle navigates over uneven terrain. Without
shocks the vehicle would bounce like a stage coach. Even though, shocks and springs
are the two main components in the suspension system. There are other components
that make up the complete suspension system like; upper control arm, upper control
arm bushing, lower control arm, lower control arm bushing, strut arm, strut rod,
shock strut, lower
ball joint, upper
ball joint and drag link, center link idler arm, pitman arm and tie rod end. Each
of these individual parts can fail over time and should be inspected and replaced
when necessary so other suspension parts don’t fail prematurely.
Let’s start with the springs. There are three common types of springs; coil springs,
torsion bars and leaf springs. We will take a look at all three commonly used systems
below and one old one. Coil springs are the most common spring used in modern vehicles
because of their compact design. The coil spring is used on the double wishbone
suspension, where the upper and lower control arms connect to the wheel spindle
and allow tire movement up and down with limited side to side movement which is
referred to as scrub. The suspension will articulate in two directions, toe angle
or steering and angle and camber angle or lean angle. There are variations of the
wishbone suspension, but basically one arm supports the weight and the other provides
control, whether the coil is above the upper arm or supported by the lower arm.
Some modern vehicle’s use a multi-arm double wishbone where all four suspension
arms work together to provide infinite adjustability. Torsion bar suspension uses
a steel bar that acts like a coil spring when twisted. The torsion bar provides
resistance when the bar is torqued, thus providing spring tension. One side of the
axle is attached to the torsion bar and the opposite end is slotted into a tube
and held in place using splines in the bar. As the suspension travels up and down
the bar is twisted and it provides spring like characteristics.
Leaf springs are used on most heavy duty vehicles today because they can support
heavy loads by adding more leafs to the stack. There is one more type of spring
that incorporates a shock and a spring. A strut is a coil over shock absorber that
connects the body to the suspension and also acts as the upper steering pivot in
the MacPherson strut. The MacPherson strut is mainly used for front suspensions
where as a similar design for the rear end is called a Chapman Strut. This design
is used often because of the space savings it provides. Shocks control the motion
the springs impart on the vehicle as it goes over bumps on the road. Shocks dampen
the motion in two directions; rebound and bounce. Basically shocks absorb that energy
by forcing the shock plunger with small holes in it through shock oil in the shock
tube. If left unpressurized, the shock oil would quickly cavitate and loose its
viscosity and working properties because of the micro bubbles created when the plunger
moves through the oil. The solution to stabilizing the oil is to pressurize the
shock so it can dampen the motion without creating micro bubbles and dissipate the
energy absorbed as heat into the atmosphere.
When a shock absorber fails, usually because it has lost pressure, the vehicle
will continue to oscillate many times more than the few bounces it normally takes
to settle. Understanding what each component does is easier when visualizing what
happens when the vehicle hits a bump. By pushing down on any corner of a vehicle
and releasing it quickly, you can see how the shocks absorb the energy and bring
the car back to equilibrium within one rebound. On a failed shock the vehicle will
continue to oscillate repeatedly with little change in frequency on that corner,
the other shocks will eventually absorb the energy, but the ride and comfort will
be negatively affected. Replacing Coil Spring and Strut Start by verifying which
system you have and the tools needed to get the job done.
Before you begin park the car on level ground with the parking brake on. Use
protective gloves, clothing and eyewear to help prevent injury.
Tools and Supplies Needed to Complete this Job
1. Floor jack and jack stands
2. Coil spring compressor (you can rent this tool if needed)
3. Air Impact Gun
4. Sockets with ratchet
5. Wrenches
6. Hammer
7. Screwdrivers
8. Replacement Struts
9. Show Towels
Instructions
Step 1 - Remove front
tires and
open hood or trunk to gain access
to the suspension system.
Step 2 - Lift and support vehicle on jack stands. Before removing tire, grab
the top and bottom of the tire and move the wheel assembly, side to side and in
and out, there should be less than 1/32” endplay between the control arm and wheel
spindle. Checking for any play before you begin is a good idea to see what else
may need to be replaced.
Step 3 - Remove front wheel
Step 4 - Remove any clips or sensors attached to the strut bracket.
Step 5 - Remove the knuckle bolts and upper stabilizer bar link and upper mounting
brackets nuts.
Step 6 - Remove spring and strut assembly from vehicle, the upper mounting bracket
may still be attached.
Step 7 - The strut assembly is under pressure and needs to be secured in a vise
before using a strut spring compressor to compress the spring. With the assembly
in the vise and the pressure held by the spring compressor, loosen and remove piston
rod nut and upper mounting brace. There may be other components like, thrust bearing
or spring seats, dust boots or bump stoppers in the strut assembly, so take note
of their order when removing them. Only do one strut at a time so you have a one
in working order on the vehicle at all times as a reference.
Installation of Coil Spring and Strut
Step 1 - Take the new piston rod and assemble the parts that make up the strut
assembly
Step 2 - Install the lower spring seat and bump stopper, dust boot, spring, spring
isolator, upper spring seat, thrust bearing, thrust bearing plate and upper strut
mount.
Step 3 - Assemble the rebuilt strut assembly using the vise. Start by securing
the upper mounting plate in the vice.
Step 4 - Use the strut spring compressor to collapse the spring so a new piston
rod nut can be tightened.
Step 5 - With the strut assembly together carefully remove the strut spring compressor.
Step 6 - Install strut assembly and tighten upper mounting bracket using new
nuts.
Step 7 - Attach the strut to the steering knuckle and tighten new nuts.
Step 8 - Attach any stabilizers.
Step 9 - Re-attach any clips or sensors that were attached to the strut bracket.
Step 10 - Check to make sure both sides look exactly the same before continuing
to the other side.
Best Practices
- Struts should always be replaced in pairs
- Use suspension grease to lube steering stops
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