Strut Your Stuff

Struts gradually deteriorate over time affecting the ride control characteristics of the vehicle. And, it typically goes unnoticed by the driver. For strut service and diagnosis procedures, read on.

McPherson-style struts have become the shock absorbing device of choice on the front suspension of the vast majority of automobiles, SUVs and minivans. The main difference between a strut and shock absorber is that the strut is also a structural suspension component. The performance characteristics of the suspension are determined, in part, 
by its position. This is in addition to its primary task of dampening the movement of the suspension.

This design has gained favor due to its compact size that allows for the installation of a transverse mounted engine and a front wheel drive (FWD) drivetrain. Traditional unequal length double A-arm suspensions provide better overall handling characteristics than the McPherson-style struts, but require more room. Unequal length double A-arm suspensions are the suspension design of choice on many race cars.

In the Chrysler Group lineup, the McPherson-style strut front suspension is found on popular models that include minivans, Caliber/Patriot/Compass, Avenger/Sebring/Sebring Convertible and the PT Cruiser. The unequal length double A-arm suspension has found its way back into the LX/LC model lineup (300/Charger/Magnum/Challenger) in both the rear-wheel and all-wheel drive layouts.

STRUT SUSPENSION BASICS

The front suspension allows each wheel to adapt to changes in the road surface without greatly affecting the opposite wheel and the ability to control the vehicle. Each side can pivot in order to steer the vehicle in the desired direction. The strut assembly 
is used in place of the upper control arm and upper ball joint (an exploded view of strut assembly is shown in Figure 1). The main components of the strut assembly include the upper mount, pivot bearing, upper spring seat, upper spring isolator, coil spring, jounce bumper, lower spring isolator and strut.

When the vehicle strikes a bump in the road, the force is transferred through the hub, bearing and knuckle and into the strut assembly to absorb that force and dampen it. The top of the strut is mounted directly to the strut tower of the vehicle (the strut tower is part of the unibody).

When the vehicle is steered, the strut assembly (through a pivot bearing in the upper strut mount) and steering knuckle (through the lower ball joint) rotate as an assembly. With the unequal length double A-arm suspension, the shock absorber does not rotate because the steering knuckle rotates through the lower and upper ball joints.

The strut assembly does not require any maintenance, but the components should be checked on a regular basis (when the oil is changed is always a good time for vehicle inspection). As a general rule of thumb, an expected service of 75,000 miles for a strut assembly is normal.

DIAGNOSIS, TESTING AND INSPECTION

Over time, the strut wears internally, leading to a slight decline in ride quality. The coil spring also loses some of its strength. This decline in ride quality, however, is very subtle and is usually not noticed, nor do vehicle owners complain about it. What usually happens is the improved ride quality is noticed when the strut assembly is replaced as part of a normal maintenance program. Failure of strut assembly components does occur, although it is not a very common occurrence.

The three most common failures are listed below in order of frequency:
1. Strut leakage
2. Worn pivot bearing
3. Coil spring break

Two of these three failures can be detected by visual inspection. Raise the vehicle and remove the wheel and tire assembly in order to have a clear view of the strut assembly. Begin by inspecting the coil spring. If the spring is broken, it will probably be at one of the two ends. Look and feel for any breaks in the spring wire.

Next, check the dust shield, or boot. Look for any tears or similar damage. Also look for damage or deterioration on the spring isolator and jounce bumper. If damage is found on any of these components, the complete strut assembly must be removed and disassembled.

Finally, check for a fluid leak from the strut (the most common failure). Lift the dust boot, as shown in Figure 2. Inspect the top of the strut, where the shaft enters the reservoir, for evidence of a significant amount of fluid. Fluid leakage more than likely will 
be seen as a stream of fluid running down the side of the reservoir and dripping off the lower end of the assembly. Remember, a slight amount of seepage between the strut shaft and seal is common and does not affect strut performance. Do not mistake this seepage for a leak that requires strut replacement.

To evaluate the condition of the pivot bearing, the vehicle must be road tested. Under normal driving conditions, steer the vehicle through a complete left hand and right hand turn. If the pivot bearing is worn, a loud banging sound will be heard on the side of the vehicle with the bad bearing. The sound is similar to that which would be heard if you struck the spring with a hammer. The sound is a result of the spring binding and releasing as the vehicle is turning.

STRUT ASSEMBLY SERVICE

To service the strut assembly, it must be removed from the vehicle. A couple of things to remember about strut service are (1) do not remove the nut from the strut rod while the strut assembly is installed, or before the strut assembly spring is compressed and (2) if both strut assemblies are being removed, mark the struts right and left according to the side of the vehicle from which the assemblies were removed.

Removal is pretty straightforward. Remove the hydraulic hose routing bracket and speed sensor cable. Next, remove the stabilizer bar link. Then, remove the two clevis bracket-to-steering knuckle attaching bolts (these bolts are serrated; do not rotate during removal). To finish the removal process, take off the three nuts attaching the upper assembly mount to the strut tower and remove the assembly from the vehicle.

To disassemble and reassemble the strut assembly, the use of a spring compressor is necessary (Strut Spring Compressor, Team PSE® tool 223-7400, or equivalent). The spring must be completely compressed (all tension removed) before the strut shaft retaining nut is removed. After the nut is removed, the spring tension is released and the assembly can be disassembled.

After the assembly is broken down, inspect the components for the following conditions and replace, as necessary:
1. Inspect the strut for any sign of shaft binding over the full stroke of the shaft
2. Check the upper mount for cracks and distortion and the retaining studs for damage
3. Check the upper seat for stress cracks
4. Check the upper spring isolator for severe deterioration
5. Check for binding of the pivot bearing
6. Inspect the dust shield, or boot, for rips, tears and signs of deterioration
7. Inspect the jounce bumper for cracks and signs of deterioration

The strut assembly is reassembled in the opposite order that it was disassembled. Remember, if both strut assemblies were removed and the springs are being re-used, the springs are side-oriented. Left side and right side springs must not be interchanged. Orientation of the spring in the strut is necessary. Consider the following in terms of degrees when placing the coil spring in the compressor:

From above, the compressor back is at 180 degrees and the operator, standing in front of the compressor, is at the 0 degree position. On short-wheelbase-based minivans, place the lower coil spring end at the 180 degree position for the left and right spring. 
On long-wheel-based minivans, place the lower coil spring end at 260 degrees for the left spring and 180 degrees for the right spring.

One more note on spring and strut orientation. Install the strut through the bottom of the coil spring until the lower spring seat contacts the lower end of the coil spring. If the coil spring is aligned correctly, the clevis bracket should point straight outward away from the compressor.