Suspension Inspection: Tips on Checking a Variety of Suspension Components
Let’s take a look at various suspension parts inspections, including ball joints, wheel bearings, wheel hub units, control arm bushings and more.
Loaded ball joints experience vehicle weight, typically at the lower control arm at the lower arm on an SLA (short/long arm) suspension, which also must be able to pivot in relation to steering linkage and the steering knuckle.
On a twin-arm suspension, the upper ball joint serves as a follower joint. A strut suspension uses a follower ball joint to connect the lower control arm, steering knuckle and the strut. The upper strut mount assembly features a thrust-type bearing to support the weight of the vehicle and allow the steering linkage to rotate the strut and steering knuckle.
Check for both axial and lateral runout. Axial runout of a ball joint basically refers to the in/out movement of the ball joint stud and ball relative to its ball socket as the stud and ball moves in-out of the socket. Lateral runout refers to movement of the stud ball side-to-side within the socket.
To check for axial runout on an SLA suspension, support vehicle weight by lifting at the lower control arm. Place a pry bar between the bottom of the tire and the ground to first determine if any axial movement is present. When dealing with a MacPherson strut front suspension, lift the vehicle by the frame or rocker panel support area and test in the same manner.
If lower ball joint axial play is suspected, attach a dial indicator to the lower control arm and position the dial gauge in a vertical position on a clean flat spot at the top of the spindle steering knuckle. Preload the dial indicator by about 0.050 inch and zero the gauge. While prying up/down, if axial movement exceeds the manufacturer specification limit, the ball joint (or the lower control arm assembly, depending on the design, should be replaced. Naturally, always refer to the runout limit specifications listed for the specific vehicle. Manufacturer specifications regarding axial or lateral joint runout limits will vary from about 0.020 inch to as much as 0.100 inch or more.
To check the follower (non-load carrying) ball joint, raise the vehicle by its frame in order to unload the joint and push/pull on the top and bottom of the tire while watching the upper joint for signs of movement.
NOTE: A wear-indicating style ball joint can quickly be checked for axial wear by inspecting the position of the grease fitting threads. If the threads are visible and protrude slightly from the ball joint, it’s probably good. If the threads have receded into the joint and are not visible, this is a sign that the joint is likely worn out and should be replaced. In addition to performing measurement checks, this is a good way of making a preliminary check.
When checking for lower ball joint lateral wear, with the wheel and tire mounted, and the vehicle raised (suspension unloaded), mount a dial indicator base to the lower control arm. Place the dial indicator plunger against the inside wheel rim and zero the gauge. Push the inside bottom of the wheel outward and note the dial indicator reading. Pull the wheel inward at the bottom and verify that the dial indicator reads zero. Re-adjust the gauge to zero if needed. Once again, push the bottom area of the wheel outward and hold in the outward position, and note the reading on the dial indicator. If the reading is beyond manufacturer specification, replace the lower ball joint.
Before checking lower ball joint lateral wear, first check and verify wheel bearing condition in the same manner to eliminate this variable. With the suspension unloaded, grasp the top and bottom of the tire and rock in/out. If any discernible movement is found, the wheel bearing assembly should be serviced (if preload adjustment is available) or replaced.
If the vehicle features an SLA suspension that locates the coil spring over the top arm, the upper joint is loaded. To check the joint, support the upper control arm to unload the joint. NOTE: If the ball joint design features a built-in wear indicator at the grease fitting location, joint play should be checked with the vehicle on its wheels (suspension loaded).
When checking a strut-type front suspension, support the vehicle at the cradle and unload the suspension, allowing the strut to fully extend. Attach the dial indicator clamp to the lower control arm and position a dial indicator in a vertical position to measure axial runout at the steering knuckle. To check lateral runout, position a jack under the ball joint and load the joint by raising the jack. Turn the steering wheel back and forth and observe the ball joint to check lateral runout.
A failing wheel bearing will result in a growling noise and/or a loose hub assembly, with either condition requiring immediate service, whether you’re dealing with a sealed or tapered bearing design. A sealed bearing is a self-contained bearing assembly caged in a carrier which is either press-fit to the hub or part of the hub assembly. A tapered bearing assembly features an inner and outer bearing, each riding on a tapered-face bearing race. A sealed bearing fails due to contamination and/or a lack of lubrication.
If a sealed wheel bearing is suspected of being worn or defective, grasp the tire at the top and bottom and rock it back and forth. If lateral play is detected, the bearing must be replaced. Sealed bearings have no adjustment feature and are not serviceable.
A tapered wheel bearing may or may not require a bearing preload. These bearings are serviceable and should be cleaned, inspected and packed with wheel bearing grease. Always check wheel bearings for excessive wear such as galling and abrasions. When subjected to overheating (due to lack of lubrication or improper preload), they appear dark/dark blue.
All wheel bearings are especially susceptible to water and dirt contamination. This is why it is so important to make sure the wheel seal is in good condition and has a tight fit around the wheel spindle. If a tapered wheel bearing (inner or outer) shows signs of dryness, galling or discoloration, always replace the bearing race(s) when replacing the bearings. Naturally, always replace the inner bearing seal. Use only the proper bearing race and seal drivers for removal and installation.
Whenever replacing tapered wheel bearings (with or without new races), always take the time to thoroughly clean all traces of old bearing grease and contaminants from the hub cavity. Grease the new bearings with high pressure wheel bearing grease using a bearing lubrication tool that allows grease to be forced into the bearing under pressure. Hand-rotate the bearing during and after grease injection to ensure complete coverage.
Hub unit wheel bearing noise
This information comes courtesy of SKF.
Wheel hub units can often wear out over a period of time due to heavy usage. As a result, ABS sensors can also break down electronically. In order to properly diagnose a vehicle before component replacement, SKF recommends performing a vehicle road test to listen for any unusual noise and to note if the ABS sensor light is on.
During the road test, if you find that the ABS sensor light is on, SKF recommends following the manufacturer’s guidelines for testing. The manufacturer guidelines may include connecting a scanner to determine which brake component system shows failure.
If a wheel speed sensor fault is detected, complete inspection of the hub unit with a sensor resistance value reading and further check the value against the manufacturer’s specification. Also verify all wiring connectors for proper fit or damage. Hub assemblies also can develop excessive endplay and/or growling noises that can affect vehicle handling or wheel alignment.
As your first step, check endplay specification. If endplay is out of specification, replace the hub assembly. Bearing failure noise can be misleading and can sometimes occur at the opposite wheel of the failed bearing. This occurs when an overload takes place during driving on the good bearing. A good way to determine bearing noise is to lift the vehicle on a frame hoist and run the vehicle at a moderate speed. This relieves the overload on the good bearing.
While staying clear of all moving parts, listen to both wheels with a stethoscope or other recommended listening device. This will help determine the location of the noisy bearing. Note that checks should be done on the spindle assembly, axle joints, wheel flanges and the vehicle frame for damage. An alignment check may be necessary to determine a bent component. It’s important to follow proper bearing installation procedures and torque specifications to avoid bearing failure or noises.
Control arm bushings
OEM control arm bushings are usually rubber or other composite flexible material. Depending on the application, bushing condition may or may not be readily visible in terms of inspection. However, inspect for signs of missing rubber, cracking or other damage.
Use a pry bar and try to move the link and bushing from side to side. Also, use a jack to load and unload the arm, while observing the bushing(s) to see if the bushing allows the arm to move in/out during arm pivoting. If excess movement is noted, or if the bushing tends to stay at one end of the pry instead of springing back, it’s time for replacement. After removing a worn bushing, if installation of a new bushing is very difficult, consider replacing with a one-piece or two-piece urethane bushing, which is easier to install. If you do opt for a urethane bushing, apply a coating of high temperature wheel bearing grease inside and out. This will ease installation and will serve to eliminate any potential squeaking noise during arm or link movement.
A vehicle that features I-beam front suspension will feature radius arms. Don’t forget to inspect the arm bushings for wear, cracking and looseness.
Begin the inspection by checking for freeplay in the steering system. With the key on (to unlock the steering column) and engine off, turn the steering wheel left and right while observing wheel movement. If the front wheels do not move during initial steering wheel movement, excess freeplay exists within the steering system (loose/worn tie rod ends, loose/worn steering box or rack, rack mount bushings, etc.).
If freeplay is found, have a helper turn the steering wheel while observing the rack and pinion body for movement at the mount bushings and tie rods. On a strut front end, also check to see if the top strut mount moves forward and rearward and inboard/outboard, which could indicate worn upper strut bearings.
A clicking or grinding sound at the upper strut mounts while turning the steering wheel could also indicate worn or damaged upper strut bearings.
When inspecting tie rods, with the suspension unloaded, apply inward and outward pressure against the wheel and tire while observing and feeling for looseness at each tie rod. A quick check of outer tie rod end looseness can be done by squeezing the outer tie rod against the steering arm to observe any axial (vertical) play. Any discernible vertical play indicates that the tie rod end should be replaced. The same applies to steering systems which feature a drag link that connects steering arms (such as on a Ford F-Series truck). Inspect the joints that attach the drag link for lateral and axial play by observing movement while the steering wheel is turned.
It should be obvious that the damping component of a strut (the shock absorber function) contains hydraulic fluid. If you see signs of oil leakage at the top of the strut tube, the seal is worn and the strut is due for replacement. Of course, replacement struts are available with or without the coil spring. Compare prices. Often, it makes economic sense to purchase a complete strut unit that includes the already-installed spring, top mount and upper bearing.
The strut’s upper bearing allows the strut to pivot as the wheels are turned. If the bearing is worn or damaged, the upper bearing can stick, causing a bind. If you turn the steering wheel while driving, release the steering wheel, and the front wheels tend to “snap” back to center, this clearly indicates an issue with one or both strut bearings. A snap or click noise may also be heard during turning. With the vehicle parked and suspension loaded, turn the steering wheel back and forth and observe (visually and listening for noise) for any binding or clicking. Replacing a strut bearing is not a difficult task (of course it requires strut removal, compressing the spring and R&R of the top hat assembly).
With the front suspension unloaded and engine off, grasp the upper area of the strut’s coil spring and push the strut inboard/outboard. Any movement of the strut relative to the body indicates a worn or damaged upper strut mount.
Naturally, inspect coil springs for breaks, cracks or coil bind. Be sure to measure vehicle ride height and compare to factory specifications. Obviously, sagging/weak springs and/or damper wear or damage requires strut and/or coil spring replacement.
Brake rotor lateral runout
A brake rotor that features excessive lateral runout will cause a pedal pulsation, along with potential spongy pedal. Lateral runout refers to the brake disc rotating in/out of the true axis (disc wobble).
Prior to measuring for lateral runout, check the condition of the hub bearing, since a worn bearing can be the cause of the runout. Also, the rotor must be secured to the hub flange with conical wheel nuts, fully torqued to the manufacturer’s specification.
Runout can easily be measured using a dial indicator. Anchor the indicator to a location that is solid and does not move along with the rotor and hub, such as the lower control arm or spindle/steering arm. Place the indicator plunger in contact with the disc surface, approximately 1/2-inch or inboard from the disc edge. Position the indicator so that the plunger is 90 degrees to the disc surface (avoid placing the indicator at an off-angle). Adjust the indicator to lace a preload on the gauge of about 0.050-inch. Zero the indicator gauge. Slowly rotate the rotor through a full 360 degrees and note the amount of runout. Always refer to the vehicle manufacturer’s runout specification.
Generally speaking, runout within about 0.002 – 0.005-inch is acceptable. If runout is excessive, this may be caused by the rotor itself, the hub bearing assembly or the hub flange. Note that excessive runout may be the result of an improperly-torqued set of wheel fasteners which can cause a deflection of the rotor hat.
Idler and pitman arms
If the vehicle is equipped with a parallelogram steering system, the idler arm and pitman arm should be checked for wear. A worn idler arm will allow excessive up/down movement that directly contributes to changes in wheel toe angles. A worn pitman arm results in excess play between the steering input and wheel toe angles.
With the left suspension unloaded, wiggle the wheel/tire in/out at the tire’s 3 and 9 o’clock positions and observe the idler arm for play. Wiggle the left wheel and observe steering wheel movement. If the wheel shows play but the steering wheel does not initially move, suspect the pitman arm.
Import air ride
This information comes courtesy of KnowYourParts.com, the industry information campaign of the Automotive Aftermarket Suppliers Association (AASA).
Just about every Asian and European luxury import nameplate manufacturer has a seven- to 10-year-old vehicle on the road with an air-ride suspension at all four corners. Chances are one of these vehicles will be coming to your shop sooner rather than later.
Most of the systems use German-manufactured air struts connected to a WABCO compressor. In between the struts and compressor are reservoirs, control valves and a lot of software controlling the system. The secret to diagnosing problems comes down to knowing what criteria the system uses to regulate the compressor/reservoir and having a scan tool that can interpret the information.
These systems do not use the compressor to directly fill the air bladders. Instead, the compressor will supply air to a reservoir that is used to fill the bladders. Some vehicles will have only one reservoir, while some may have multiple reservoirs. The reservoir is equipped with a pressure sensor and valves to send compressed air to the spring and exhaust excess pressure. Do not work on any reservoir unless the system is allowed to depressurize before performing any repairs. Some systems may require the use of a scan tool to release the pressure and re-pressurize the system. The reservoirs are typically made of aluminum. They can be located in the trunk or tucked behind fenders or quarter panels. It is rare for the tank to develop a leak, but it is common for the air-line connections.
Air-ride systems look for information like vehicle speed, ambient air temperature and ride height. From this information, a system can calculate how long the compressor should run to fill the reservoir. If it is taking too long, the air-ride module will set a code, alert the driver, and put the system in a safe mode.
The codes for this type of problem will typically include the words “replenish,” “reservoir,” “overheat,” “no pressure increase” or “timed out.” There are two main culprits for these codes — a weak compressor or a leak in the system. It is possible that a sensor in the reservoir is faulty, but this is extremely rare.
The control module will not immediately turn on the compressor when the engine is started and will trim the suspension from the air in the reservoir. Some systems will not engage the compressor until the vehicle has reached a predetermined speed like 25 mph. These rules are in place so moving air will cool the compressor. That way, the driver will not notice the compressor operating while the vehicle is stopped. But, in some cases, the compressor will run during startup if the pressure is low enough.
All four-corner systems are using air from the reservoir even if the car is parked. This is because as the vehicle cools, the air volume and pressure in the bladders and reservoir will decrease. The system will trim the ride height to make sure the vehicle is not sitting on the ground when the driver returns to the vehicle in the morning. Also, some systems will keep a level ride height if the vehicle is parked on an uneven surface, or the vehicle is unlocked and a load is placed in the trunk. But, most systems will never turn on the compressor to make a key-off correction.
Before a vehicle is returned to a customer, you should perform a calibration procedure for the air-ride system, if required. Calibration procedures typically involve measuring the four ride heights and entering the data into the scan tool. Not performing this procedure can lead to a comeback.
Don’t turn away air-ride problems from your shop or steer them to the dealer. The parts and tools are available to restore an air suspension to full-operating condition, or even convert the system to conventional springs. Always advise the customer that not repairing the air-ride system will remove some functionality from the vehicle, such as adjustable ride control and load leveling.
With more air-ride-equipped vehicles accumulating miles, you can expect to see a steady stream of these air-ride systems in your bays. You also have more options than ever before when it comes to aftermarket replacement parts and conversion kits. ■