Servicing Suspension Struts Requires Attention to Detail
When a customer comes in and says the car is not riding “right” or there’s a clunking sound from underneath, it’s important to do a thorough investigation before jumping to any conclusions. When the vehicle has a strut suspension, you need to understand how all the components work together and which ones are most prone to wear. Here are strut service tips that should be used whenever working on vehicles.
In this article, we’ll discuss basic strut removal, service and installation. Let’s dive right into it.
With the vehicle raised, and before removing the wheel assembly, place a matchmark on the wheel stud that is closest to the air valve stem. This will provide a reference to reinstall the wheel in the same position. Just in case there is a stack-up of tolerances between the wheel and hub, this avoids the potential of creating a lateral runout condition and resulting vibration that could cause a comeback.
Once the wheel is removed, detach any items that are currently secured to the strut body such as an ABS wire harness, anti-sway bar end link and/or brake hose.
Disconnect the lower strut mount. Depending on design, this may involve either a two-bolt bracket that’s welded to the strut body, engaged onto the knuckle upright; or a tube-through mount where the bottom of the strut tub is captured in a split bore at the top of the knuckle, secured with a horizontal pinch bolt.
With the pinch bolt removed, you will likely need to “persuade” the tube from the knuckle by striking the knuckle downward with a brass hammer.
Depending on suspension design, this might also require lower ball joint disengagement, or, once the upper strut mounting nuts have been removed, you may be able to wiggle the tube from the knuckle. If possible, the lower strut mount should be free before you remove the upper three strut mount nuts.
NOTE: You may encounter older strut designs that feature the strut tube with an integrated lower bracket that secures to the steering knuckle with two vertical bolts, accessed from the underside of the steering arm (the Datsun 280Z is an example).
With the lower strut mount free, remove two of the three upper mount nuts and loosen but do not remove the third nut (if the design features only two nuts, remove one and loosen the other). This prevents the strut from dropping. While holding the strut with one hand, remove the remaining top nut and remove the strut assembly from the vehicle.
NOTE: Do not loosen or remove the center nut that secures the strut’s piston rod.
If you plan to replace only the strut unit while maintaining the upper seat, bearing and coil spring, once the strut assembly is removed from the vehicle, wipe the bulk of dirt and grim from the assembly and wear safety glasses. Using a quality coil spring compressor designed for strut service, engage the tool jaws onto the coils, as close to the top and bottom as possible. The tool should be either wall-mounted or solidly secured to a large bench vise. To minimize the danger of accidental and unexpected coil spring release, make sure that the top of the strut assembly faces in a safe direction, aimed away from people, vehicles or equipment.
Before beginning disassembly, use chalk to place matchmarks along the upper hat, spring and main body to use as a reference during reassembly.
With the coil spring captured solidly, begin to compress the coil spring until spring pressure at the top hat is removed. Use an impact wrench to loosen and remove the top nut that secures the upper hat and bearing assembly and spring. If the shaft spins and prevents the nut from turning, examine the upper tip of the piston rod. If it features a male or female hex, you can engage a box wrench or hex bit to hold the rod steady while loosening the nut with a box wrench.
Remove the upper hat/bearing assembly and slowly and carefully relax the spring and remove the spring from the strut. Remove the boot and rebound bumper. If the boot and/or bumper are damaged, plan to replace with new parts.
Always replace all mounting hardware, including upper tower nuts, upper piston rod nut and lower mount bolt(s).
Compare the new strut to the original to verify length and mounting designs.
Discard the original strut according to state and local regulations.
If the new strut has been stored horizontally for a long period (and if the strut is not a gas-charged design), initial movement of the piston rod may seem soft. You can easily prime the strut by compressing and releasing the piston rod a few times until the expected resistance is felt.
In some older designs, the strut tube and lower spring seat are to be re-used by removing the shock cartridge from the strut tube. This may be secured with a thin profile, large diameter hex nut. If this is the case, plan to replace the hex nut, since it’s likely that you’ll damage the original during removal.
Before assembly of the strut package begins, lubricate the exposed piston rod in the area where the rebound bumper will be located, using wheel bearing grease, silicone grease or lithium grease. Depending on the strut brand, a piston rod lubrication recommendation may be included in the instructions.
Closely examine the coil spring, checking for cracks, severe rust or heavy nicks that might act as stress risers. If damage is found, replace the spring. If the strut features a replaceable cartridge, be sure to clean the lower spring seat to remove any debris or rust. Again, if the lower spring seat is badly rusted, replace the strut body. If any dents are found on the strut tube, the strut body must be replaced, as any deformation in the tube can interfere with internal piston and seal travel.
If the coil spring features rubber or plastic isolators at the upper and/or lower coils, replace with new if damaged. If using a new spring, be sure to install these isolators to the new spring.
Install the rebound bumper, in the correct orientation, to the piston rod. Carefully compress the coil spring and pace it over the tube, registering the lower coil in the correct and originals clock position. The lower spring seat should feature a positive stop where the lower end of the spring seats.
Compress the spring far enough to allow installation of the boot and upper assembly. Insert the boot and upper assembly, registering the piston rod tip through the upper hat. Install the new piston rod nut as far as you can to engage at least half of the nut thread depth.
Referencing the previous matchmarks, align the spring and upper hat assembly in the correct clock position.
While holding clock position, slowly relax the spring tension until the upper hat assembly secures the spring. Verify that the upper mount bearing is free to rotate. Snug the piston rod nut to further secure the assembly. Avoid using an impact wrench to tighten the piston rod nut, as this can easily cause the rod to spin. Fully release the spring compressor and remove the strut from the tool.
Always use a new top piston rod mounting nut, whether reinstalling the original strut or replacing with a new strut. New struts will usually include a new piston rod nut. If necessary, new nuts may be obtained from your ride control supplier. Thread integrity and overall strength is critical, since a nut that fails or loosens will allow the strut piston rod to oscillate needlessly and potentially fail.
These nuts also often feature a “locking” design in the form of a slightly distorted upper inside diameter (often referred to as a self-locking or “stover” nut) or a nylon insert that prevents accidental loosening. These nuts are considered non-reusable and must be replaced.
Use caution when loosening or tightening the upper piston rod shaft nut. The strut’s piston shaft may rotate as the torque is applied to the nut. If the strut is to be re-installed, do not use an impact wrench to remove the nut, as this may cause the shaft to rotate or spin quickly, which can gall the threads and damage the internal seals via friction and heat. When installing a new or used strut, by the same token, do not use an impact wrench. Strut shaft upper tips vary by design, but a provision for holding the shaft in place to prevent rotation should be featured.
This allows you to use an open-end or box wrench to hold the shaft stationary while turning the nut.
In some cases, a specialty wrench will be required to secure the shaft. Never use pliers or a vise-grip to secure the piston rod in place, as this will create burrs on the shaft, which will result in internal damage.
Of course, in certain cases, a technician will be forced to do whatever he or she must do in order to remove an original worn or damaged strut. However, never use pliers to secure the piston rod on any strut that will be final-installed.
If you plan to install a new complete strut assembly such as Monroe’s Quick Strut or Gabriel’s ReadyMount strut, insert the top of the assembly into the strut tower, aligning the three upper mounting studs to the tower holes and snug-install one upper new nut. Do not fully tighten or install the remaining nuts yet. This allows the strut to pivot freely while engaging the lower strut mount, which reduces the risk of damaging the upper strut bearing.
Install the lower strut mount, installing two new bolts to secure the strut bracket to the knuckle; or in the case of a slip-tube lower body, engage the tube at its correct depth and install a new pinch bolt.
Fully torque the lower mounting bolt(s). Install any accessories that were previously removed from the old strut body such as ABS wires, brake line and/or anti-sway bar link. Torque these bolts to the specified values.
Install the wheel, referencing the matchmarks to ensure that the wheel is installed in its original clock position.
Lower the vehicle, loading the suspension. At this time, fully tighten and torque to value the upper strut mounting nuts that secure the strut to the tower. Also fully torque the upper piston rod nut. Again, hold the piston rod steady while tightening its nut, taking advantage of the piston rod’s top male or female hex. Waiting until the suspension is loaded to torque the upper nuts ensures full strut engagement inside the tower and eliminates the risk of damaging or weakening the upper strut mounting studs, as opposed to pulling the weight of the strut and control arm upwards as the nuts are tightened. This also ensures that the piston rod is fully engaged on its threads.
Always replace struts in axle pairs. If the right or left side strut is new and the opposite strut is aged, a considerable difference in ride control can occur, leading to poor and often unpredictable handling and braking.
If a strut on one side of an axle has worn or failed, the opposite side strut is likely in the same condition. This may seem like common sense, but consumers on a budget may be reluctant to spend money for something that they assume is not needed. Stand your ground and insist on replacing the pair, making it clear that this is in their best interest in terms of safety. Always replace in axle pairs.
Notes on the lower mount
As mentioned earlier, the most common styles of lower strut mounting design may feature either a bracket that secured to the upright and cinched with two bolts, or a slip-fit that enters the knuckle upright’s split bore, with a pinch bolt that creates a tight interference fit.
When removing a strut assembly that features a slip fit lower mount, after removing the pinch bolt, it’s likely that a tight interference fit remains, making it difficult to remove the lower strut body from the upright.
Using a wedge tool, the split bore may be separated slightly at the gap in an effort to spread the bore. Adding a penetrating oil may help as well.
Using a brass or aluminum hammer, striking the split bore housing downward may help to dislodge the strut tube body, in addition to pivoting the spindle/upright unit across the strut tube.
Before installing a new strut assembly that features a slip-tube-to-split collar knuckle, make sure that the split tube bore is clean and free of burrs that may have been created during removal.
A honing stone or a grinding stone on a pneumatic die grinder can be used to clean the bore. During reassembly, always install a new pinch bolt and nut.
Before inserting the lower strut tube into the upright’s pinch bore, apply a film of anti-seize in the bore. This will aid in assembly and should ease future removal.
If the lower strut mount features a two-bolt bracket, before installing the new strut, clean the upright surfaces to remove any rust and/or burrs.
Only use sandpaper or emery cloth to clean the upright’s mating surfaces to avoid removing excess metal. Always install two new bolts and nuts to secure the lower mount.
The two-bolt lower bracket bolt holes in both the upright and strut bracket will likely feature enough tolerance to alter the wheel’s camber angle.
Always perform a wheel alignment following front or rear strut service. Even if the lower strut bracket holes are not elongated to accommodate camber adjustment, the holes may provide a minimal amount of adjustment.
In some cases, such as the Ford Taurus series, it’s very common for the pinch bolt that secures the lower strut tube body to the knuckle to be badly rusted in place. It’s not uncommon to fracture and break this bolt when attempting removal with a strong impact wrench.
Rather than risking this, first place a matchmark on the bolt head and knuckle. This will provide a reference to see if the bolt is turning when you do attempt removal. If time allows, let the oil soak overnight before wrenching.
If the bolt does not begin to rotate, apply heat, being careful not to damage adjacent surfaces. Once the bolt area is hot, apply more penetrating oil, allow the area to cool for a few seconds and attempt to remove the bolt. It may be necessary to repeat these steps several times until the corrosion breaks down enough for bolt removal.
If the bolt does break, you’ll need to drill it out. In the process, you’ll unavoidably drill out the female threads in the knuckle. In this case, you’ll need to install a new, longer bolt and a nut to complete the installation. Be sure to use a grade 8 bolt and nut. Consider using a lock washer on the nut side.
NOTE: Some vehicles, such as a 2010 Ford F-150, features front shocks with captive coil springs that at first glance may appear as struts.
However, this suspension features upper and lower control arms. The damper assembly is simply a coil-over shock absorber with an upper spring seat and a lower eyelet style mount and is not considered a strut.
Vehicle leans: If the vehicle tends to exhibit excessive lean in turns, and during braking or acceleration, check the condition of the coil spring(s), strut assemblies and damaged, worn or missing anti-sway bar bushings/links. A worn strut assembly may feature a worn or broken coil spring and/or a worn damper, whether the damper is of hydraulic or hydraulic/gas design.
Front end shimmy: Suspects include upper ball joint (if so equipped), upper control arm bushings (if so equipped), lower control arm bushings, inner tie rods, the hub assembly, and a FWD driveline (CV shaft assembly). Check tires for proper inflation. Underinflated tires can cause a shimmy.
Also inspect for improper tire size matching on the same axle. Tires of different diameters, or tires of different brands or even different tire models within the same brand, can cause this issue.
Uneven or premature tire wear: After checking the obvious concern for proper tire inflation pressure, this issue can be caused by any of a number of variables, including incorrect wheel alignment, worn control arm bushings, the strut assembly, inner and/or outer tie rods, lower control arm ball joints and upper arm ball joints (if so equipped).
Diagnosing tire wear is a subject unto itself. Premature tire wear can result from the use of tires that feature (relatively) softer tread compounds, as found in many high performance, high-speed-rated tires, as well as tires that are specifically designed for cold weather snow/ice use.
Softer compounds tend to wear faster, especially on dry road conditions where the coefficient of friction is greater as opposed to wet, snow-covered or ice-covered surfaces.
By and large, premature tire wear, especially where tread wear appears uneven, is usually the result of improper inflation, incorrect wheel alignment or worn/damaged steering and/or suspension components.
Excessive wear found only at the outer tread areas and shoulders is likely the result of aggressive driving in turns and curves, inadequate wheel camber angle, or a combination of both.
Excessive steering wheel play: Potential faults can include a worn or damaged steering rack, inner and outer tie rods, hub assembly, lower control arm bushings, upper control arm bushings (if so equipped), or CV shaft joints/assemblies.
Always verify a customer complaint regarding steering wheel play.
If the vehicle was previously serviced, and the steering wheel was removed at any point, check for in-out play which can indicate that the steering column shaft nut was not properly tightened.
Steering wheel vibrations: Vibrations felt through the steering wheel can result from a range of issues, including wheel imbalance, radial tire force variation, CV shaft assembly issues including worn/damaged CV joints and/or the loss of a damping device from a CV shaft, loose/worn hub bearings, or improper brake caliper action resulting from brake rotor runout or a dragging or sticking brake caliper.
If brake pedal bounce is felt in addition, suspect brake rotor runout issues.
Note that improperly tightened wheel fasteners may also contribute to a distorted brake rotor.
Grinding or cluncking noises: Unusual noises emitting from the front end of the vehicle may involve a wide range of potential issues.
- Upper strut mount (mount lose or mount bearings worn/dry/damaged).
- Coil spring damage (cracked, failed spring) or an improperly seated coil spring.
- Control arm bushings
- Strut assembly itself (worn/damaged damper, piston shaft, spring, lower strut mount, improperly assembled strut)
- Inner and/or outer tie rods
- Anti-sway bar bushings/links (damaged, worn or missing)
- Hub bearing assembly
- CV shaft assembly
- Brakes (loose or sticking brake caliper/pads; a foreign object such as a small rock wedged between a pad and rotor)
- Wheel clearance (if a non-original wheel with incorrect backspacing or diameter has been installed, check for clearance at the caliper)
Front end pulls right or left: If a directional pull is present, first check all tires for correct inflation pressure. Also check tire sizes for mis-matched sizes on the same axle, and for mixed tire brands/models on the same axle. Inspect wheel alignment angles, since incorrect toe, camber or caster angles can easily result in a pull.
Suspension components of concern include upper strut mounts (worn, dry or failed strut mount bearings can affect steering axle dynamics, reducing the right or left wheel’s ability to follow steering wheel commands).
Other suspect components may include control arm bushings, coil spring condition (weak, sagging spring, improperly installed spring or damaged spring), lower ball joints, upper ball joints (if so equipped), and inner/outer tie rods. ■