Mechanics

Strut Replacement

Strut Assembly
How to Replace Struts

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
If further technical assistance is needed, our certified car repair technicians are ready to answer your car questions. For manufacturer specific repair information visit - Car Repair Manuals

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AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-08-16)