Diagnosing chassis issues, including noise, vibration and drivability concerns ranges from the simple to the difficult-to-pinpoint. In this article we’ll discuss a variety of tips, both vehicle-specific and generic. As part of the article, we’ve included insightful comments from Federal-Mogul Motorparts and Arnott.
Following are a range of applicable comments by Mark Isaac, Federal-Mogul Motorparts master instructor in the firm’s Garage Gurus program.
Today, we’re seeing more bushing failures, for example in lower control arms with vertical bushings. We see lots of rubber deterioration. As this continues, increased arm movement occurs where the bolt is vertical. Ball joint and tie rod wear, as you might expect, is more common on heavier vehicles such as trucks, as opposed to lighter passenger cars. With the increased population of crossover vehicles, we’re also seeing more ball joint and tie rod wear as compared to lighter, compact passenger cars.
Light truck owners often present additional challenges when they “upgrade” to larger wheel/tire combinations. Increased loads are often presented to suspension and steering components. Noticeable shimmy/wobble issues can easily be created, most commonly on trucks that feature a solid front axle when greater wheel offsets and/or larger tires are installed, magnifying the shimmy or wobble. In severe cases, a “death wobble” can be created that intensifies in relation to speed. Tie rods can take a beating, and ball joint bolt holes can wear mounting holes eccentrically.
Lifting or lowering the truck also can create odd and wear-inducing angles to pitman arms, steering arms, etc. Some aftermarket ride height altering kits are available to compensate, in an attempt to place the steering component angles back in plane, but if correct components and procedures aren’t employed, altering the truck’s ride height can create a host of steering control and component wear issues.
Brake line corrosion, particularly in Rust Belt areas where salt/brine is placed on roadways, is a real problem. Regardless of the coatings applied to some lines, the corrosion problem hasn’t gone away.
Regarding strut suspensions, the weak link is the upper bearing, as this experiences the weight of the vehicle. In Rust Belt areas, this issue increases.
Pay attention to coil springs in terms of fatigue and fracture. Rust, cracking and fracture seem to be more common with smaller gauge coil wire, especially at the bottom where the coil sits in its seat, where water and salt collects. Struts that feature a pinch bolt mount at the bottom (as opposed to twin bolts at a flange), strut tubes can bend on hard impacts/rough roads.
One notable issue that we’re seeing lately is increased failure of aluminum steering knuckles and control arms. The softer metal is conducive to tapered bores wearing out-of-round due to neglect or improper installations. As the holes wear, the studs move around and the wear is accelerated. Proper fastener tightening is critical. We really need to stress torquing fasteners to the OE specification to avoid this.
From a service standpoint, we’re seeing a substantial move toward using complete assemblies, as opposed to repairing/rebuilding. Examples include complete strut assemblies, as opposed to dismantling and replacing the damper, and potentially the coil and the upper bearing. Installing a complete strut assembly has the advantage of everything being new, and substantially reducing shop labor time and offering the customer a faster turnaround.
The same concept of offering complete assemblies has now expanded to include complete control arms (that include new bushings and ball joints), complete steering systems, especially on heavier (truck) systems (tie rods, adjuster sleeves, etc.), as well as complete knuckle assemblies that include pre-installed bearings, eliminating the need and time required to press out old bearings and press in new bearings. This increasingly popular trend of using complete assemblies is less labor intensive, ensures a quality repair that requires less time.
When a CV joint boot is open (torn, loose, allowing contaminants to enter and grease to exit), the joint will soon fail. Warning signs include a clicking sound, especially during slow turns, which indicates a bad outer joint. A rumbling noise/feel is indicative of a failing inner joint.
Hydraulic motor mounts (Honda applications are a good example) can wear and begin to experience changes in damping speed, which eventually lead to failure and result in separation.
Power rack & pinion steering systems can develop a “mystery” leak which may not be visible externally. A slight air leak in the remote fluid reservoir to the pump circuit may cause air to be drawn into the system on the suction side with no signs of external leakage. If air enters the system, it can’t bleed itself. We find this most common on Honda and Acura vehicles, but the problem can present itself in any hydraulic power system. In order to diagnose this, place a slight pressure to the reservoir using a radiator pressure tester at 1 psi to 2 psi. While pressured, look for fluid leaks at hoses and connections.
Wheel bearing issues sometimes don’t exhibit looseness and may feel tight, even though the customer may have noted a “strange noise.” A handy diagnostic tip is to hold your hand on the coil spring and rotate the wheel by hand. A worn or failing wheel bearing can show itself if you feel a slight resonance/vibration through the spring.
Wheel alignment procedures are changing, often requiring additional steps, thanks to the proliferation of on-board electronics. For example, on vehicles that feature a steering angle sensor, when wheel toe angle is adjusted/changed, on some applications the sensor automatically recalibrates, while on some vehicles a scan tool must be used to command the sensor. Active steering, autonomous braking, long range radar, infrared, cameras, etc., may need to be re-set, especially if the vehicle has been involved in a collision due to sensor alignment angles being misaligned. Wheel alignments are becoming more complex due to these additional features. The OEMs provide set procedures for vehicles that feature these systems.
Air suspension concerns
Problems with air suspension systems present a range of unique issues. The engineers at Arnott were kind enough to provide the following information.
Air suspensions are found on many luxury cars, trucks and SUVs. Air suspension serves the same purpose as a standard coil spring suspension system but instead of using metal springs — it uses inflatable air springs filled with compressed air to level the vehicle.
Many consumers miss the early warning signs of an air suspension issue — unfortunately these problems only get worse, and more expensive — over time.
The main signs of air suspension problems include:
The dashboard warning light: One of the obvious signs of an air suspension problem is when a dashboard warning light comes on. Even if the light doesn’t stay on, the vehicle should be checked.
Suspension sagging: One of the first signs of an air suspension problem is when a car sags in a corner or entire side. Typically this is due to the rubber air spring developing tiny cracks or holes because of dry rot or road debris. If a customer notes that their vehicle drops in height overnight or after they park, they most likely have leaks in their air spring or strut.
Air suspension compressor constantly working: If there is damage to the air springs then the compressor will constantly be pumping air to keep the air bladders inflated. If the compressor is constantly running, the system should be examined as soon as possible.
Compressor not working at all: The air suspension system cannot function without the compressor. If the compressor does not come on at all, that may be a sign that it was overworked and has burned out or it could be as simple as a fuse or relay problem.
Compressor making noises: The owner may also notice abnormal noises during compressor operation such as loud clicking, whining or grinding. This could be a sign that the compressor has been overworked or there could be excess moisture in the system because the compressor’s dryer is saturated.
Once the compressor has been replaced the rest of the system including the air springs and struts should be tested.
Other suspension issues also may apply to air suspension including:
* The vehicle bottoms out over bumps or rides roughly.
* It nose dives when stopping.
* The vehicle pulls to one side or steering is difficult.
* The car continues to bounce after hitting a bump.
* Uneven tire tread wear.
* The shock portion of the strut appears to be oily or damaged.
If the customer complains about any of these symptoms or if the vehicle is over five years old or has over 50,000 miles, you should inspect it for signs of air suspension damage.
If the vehicle’s dashboard suspension warning light comes on, but the car seems to be maintaining its height, you should use a scanner to diagnose the fault code. Typically, this is an electrical problem such as a relay or fuse.
If the vehicle sags at one corner or side the easiest way to diagnose the air suspension problem is to put the vehicle on a lift and perform a visual inspection of the air struts and springs, the ride height sensors, air lines and connections and the compressor. To locate leaks in the air suspension system, spray the air bladders, fittings and lines, and top seal with a solution of dish soap and water and look for bubbles.
There are multiple options for repairing and replacing a leaking air spring or strut. New OE springs, struts and compressors are expensive at dealerships but aftermarket vendors offer options that cost far less than the dealership. Arnott, for example, offers new OE quality compressors as well as new replacement air springs that are often easier to install than the OE and built with heavier-duty rubber. They also offer both new aftermarket replacement struts that they design and assemble and remanufactured OE struts.
If a vehicle has multiple air suspension problems or has had a long history of issues it may be more cost effective to replace the air suspension with a coil conversion kit. Some kits cost about the same as a single air strut at a dealership but should provide many years of trouble-free driving.
The bottom line is air suspension repairs are not difficult to diagnose or fix. You should be inspecting they systems after 50,000 miles and customers should be encouraged to repair their air suspension problems quickly before one problem turns into multiple, more expensive, problems.
Ride control issues
Ride control, in terms of both handling and noise concerns, are common complaints. Quite often, the customer’s description is vague or misleading. Attempt to gather as much information from them as possible prior to performing an inspection.
For example, do you only hear a “funny” noise when driving on bumpy roads or on smooth roads, as well? If you suspect that the vehicle is heavily loaded with cargo at times, ask if the “wandering” they experience only occurs when heavily loaded, etc. The customer’s descriptions of an issue should be considered merely as a starting point. It’s up to you to inspect and road test to determine the actual cause of the complaint.
Prior to any chassis-related issue, always begin by checking the basics, including tire size, tire inflation and vehicle ride height. These basic checks can help to quickly identify contributing factors with regards to directional pull during cruising and braking, as well as wheel alignment issues and potential cause for uneven or premature tire tread wear.
A directional pull while driving can involve any of a number of issues. Begin by checking tire size, verifying that both tires on the same axle are the same size. If a previous tire replacement resulted in only one tire being replaced of a different diameter, the smaller diameter tire will cause the vehicle to pull in the direction of the errant side. For instance, if the left front tire features a smaller diameter as compared to the right front tire, the vehicle would tend to pull to the left. All tires should ideally be the same make and model, and overall tire diameter should be the same at both sides of each front and/or rear axle.
Improper inflation pressure is one of the leading causes for a directional pull. Depending on the sensitivity of the suspension design, as little as a 3 psi change per axle side can account for a pull. The pull will occur at the side that features the lower inflation pressure. The severity of the pull will depend on the comparative difference in the same axle’s tires. Tire inflation differential isn’t limited to the front steering axle only. Uneven rear tire inflation can cause a pull, as well.
Wheel alignment angles due to suspension and/or steering component wear can have a profound effect on the vehicle’s tendency to pull in one direction. This includes toe, camber and caster. Excessive toe-out on one side can cause the vehicle to pull in the direction of side with more toe-out. If camber angles differ (beyond specification), the vehicle will tend to pull in the direction of the wheel that features more negative (or less positive) camber angle.
For instance, if the left front wheel has negative 1 degree of camber while the right front wheel has 1.5 degree positive camber, the vehicle will pull to the right. While the caster angle on many common vehicles may not be readily adjustable, uneven left/right caster angle that is beyond specification can easily cause a pull, with the pull taking place at the side with less caster angle.
As an exaggerated example, if the left front wheel has a caster angle of 0.5 degree positive and the right front wheel has a caster angle of 2 degrees, the vehicle will pull toward the left. Worn ball joints, control arm bushings, tie rods (and tie rod ends) allow excess movement of control arms and steering knuckles.
Brake drag can cause both an accelerated brake pad and rotor wear issue and a directional pull. If the caliper pistons on one caliper do not retract fully (during non-braking or after a braking), the pads can retain enough rotor contact to reduce the free-wheeling operation of the rotor, in which case the pull will result toward the side with the sticking caliper.
Sticking/stubborn caliper pistons can be caused by corrosion in the piston bore as the result of moisture contamination, or following a brake pad replacement after the brake pads have been allowed to severely wear. If the vehicle was operated with thin pads for an extended period, the caliper piston travel distance within its bore has been limited, with possible rust/contamination building up in the unused area of the piston bore. Once the new pads have been installed, this causes the piston(s) to be further retracted, now travelling win a non-smooth area of the bore, potentially resulting in the piston being slowed down or stuck in the contaminated bore area.
If a vibrational complaint involves the problem occurring during braking, the most likely cause is a warped brake rotor, causing the pads to bounce on/away from the uneven rotor surface. Brake rotor warpage can result from various causes, including brake rotor overheating, lateral or radial runout, sticking caliper pistons and even improper wheel fastener torquing.
Many passenger cars today feature thin-hat rotors that are easily distorted if the wheel fasteners are unevenly or excessively tightened. This is another reminder that a calibrated torque wrench should always be used, especially when installing alloy wheels. Avoid the use of impact wrenches during wheel installations, and always tighten to factory specifications, following the correct tightening sequence.
Check brake rotors for lateral runout. Lateral runout causes the rotor to “wobble” as it rotates, kicking the brake pads in and out during braking, resulting in pedal bounce. When checking lateral runout, the rotor must be secured to the hub with all wheel fasteners (not only two or three wheel nuts or bolts), with fasteners torqued to specification.
Mount a dial indicator base to a solid and non-moving surface and lace the indicator plunger perpendicular to the rotor disc surface. Preload the plunger by about 0.050 inch and then zero the indicator gauge. Slowly rotate the rotor a full 360 degrees and observe the movement of the gauge needle. Compare your reading to factory specifications. Generally speaking, lateral runout exceeding 0.0025 inch is too much and may require rotor replacement.
However, before replacing an otherwise acceptable rotor, mark the orientation of the rotor to the hub (matchmark one wheel stud and its adjacent location relative to the rotor). Remove the rotor and re-position it to the hub in the next clock position and re-check for runout. You may have a stack-up of runout tolerance between the rotor and the hub. If you start to see an improvement, re-position the rotor to the next clock position and re-check. It may be possible to find that “sweet spot” where hub runout and rotor runout cancel each other out.
A “noise” complaint has the potential for covering quite a lot of ground. Try to obtain more detailed information from the customer. What type of noise do you hear? (clicking, groaning, grinding, popping, whirring, whistling, chirping, banging, etc.). When do you hear the noise? (while starting the engine, while cruising, during braking or turning, or when braking).
Worn front wheel bearings will typically produce a grinding or clicking sound. Worn or damaged upper strut bearings will typically produce grinding, squeaking or popping noises best heard during slow turns. Worn or dry CV joints will cause a clicking noise, usually experienced during a slow turn (into a driveway or parking spot).
If the vehicle features front-wheel drive and the rear suspension features a Watts link (also called a bell crank), it’s not uncommon for a worn Watts link center bushing to be worn out, which will result in a banging noise as the vehicle is driven over bumps or uneven road surfaces. This is often misdiagnosed as involving loose or worn-out rear shocks/struts. A worn-out Watts link won’t really cause any major drivability issues, but the resulting banging noise can be quite nerve-wracking, making the vehicle owner concerned about a major problem.
A “quick & dirty” check when trying to isolate a suspension noise is to unload the suspension (car jacked up or on a frame lift) and whack the center of the tire tread with a large hammer, while listening (and feeling with your hands) for noises at control arms, sway bar links, wheel bearings, etc. This basically allows you to attempt duplicating the tire hitting a pothole. This old-school technique can often let you determine a worn suspension component.
A “shake” complaint by the customer in somewhat ambiguous, since the issue may involve a vibration or a “shake.” Potential wheel imbalance is an obvious starting point. A road test will help to confirm this. If you suspect a wheel imbalance, and you check the wheels on a balancing machine and find no issues, consider a road force variation issue, where the construction of the tire(s) features isolated hard spots. This may be verified and remedied by using a balancing machine that features a road force simulator.
Other potential factors might include a driveshaft imbalance. Inspect the driveshaft for a missing balance weight and check for worn front and rear universal joints. Also inspect for a bent or dented driveshaft. If the vehicle features rear-drive and a solid axle housing, check the pinion angle. If the axle assembly pinion angle has been moving vertically, this changes the driveshaft angle, which could explain a shaking or vibrating issue. If the rear suspension features leaf springs, inspect the spring mounts and spring pad U-bolts for wear and looseness.
Severely worn shock absorbers (independent shocks or strut dampers) prevent controlled vertical wheel travel, reducing correct tire-to-road surface contact pressure, resulting in a “floating” sensation at highway speed. In combination with speed-related vehicle air resistance, this can give the driver a feeling of a light, “wandering” condition. Worn shocks/dampers will allow over-travel of the suspension, allowing excessive body lean in both lateral (side to side) and longitudinal (front/rear) planes.
The reduction of damping and spring harmonic control leads to not only directional wander and body lean during cornering but nose-dive during deceleration and braking, as well as noticeable wheel hop, since a failed shock is not able to control suspension spring oscillation. While signs of hydraulic oil leakage are indications of wear, internal pistons and seals may be worn with no observed fluid leaks.
Since poorly performing or worn-out shocks/struts don’t control the suspension properly, this creates a domino effect by placing greater loads and stress on other suspension parts such as control arm bushings, springs, anti-roll bar bushings, lateral links, etc.
Worn steering system components, such as tie rod ends, drag links, steering gears, rack mount bushings, worn or loose pitman arms or idler arms, pitman arm or idler arm mountings are all suspects when inspecting for a wandering complaint.
Check the condition of the w
heel bearings. Loose or worn wheel bearings will result in excessive lateral wheel play, easily contributing to a sometimes twitchy wander issue.
Moisture contamination is one of the primary causes of roller or ball bearing failure. Moisture leads to bearing overheating, deterioration of bearing grease and corrosion and bearing noise.
A drone or whirring noise can often be misdiagnosed as a wheel bearing issue, where uneven tire tread wear may be the actual cause. Noises tend to travel and may be generated by a wide range of chassis components, sometimes making pinpoint diagnosis difficult.
Chassis ears, a somewhat generic term for equipment that allows you to monitor noise and vibration, can be extremely useful for pinpointing issues with a wide variety of components. Currently available chassis ears offer ease of use and outstanding diagnostic capabilities.
An example is Steelman’s Wireless ChassisEAR. The control unit/receiver is wireless, powered by AA batteries. The kit includes four vibration/noise transmitters, each powered by AAA batteries. Simply attach the transmitter(s) to the area or component you wish to test. Attachment methods vary, depending on the mounting surface.
The transmitters feature two internal magnets that allow a secure mount to an appropriate surface, although the magnets don’t appear strong enough to hold well on rusty or greasy surfaces. If the surface mount area won’t provide a reliable hold, provided Velcro straps can be used to secure the unit, which provide a very secure grip. Each transmitter also features a strong spring clip, so depending on the mounting surface, you have three mounting options. Each transmitter accepts a plug-in cable that features a spring clamp. Attach the clamp close to the area/component that you wish to monitor.
Each transmitter is boldly identified with a number (1, 2, 3, 4), with corresponding illuminated push buttons on the receiver. While the receiver features transmitter-related buttons and a row of noise-intensity LED lights that provide a good visual signal, it’s best to also plug in the supplied earphones that allow you to hear noises.
Take the vehicle for a test drive, and press the button (channel) desired and listen for noises. This makes it easy to compare, for example, left and right wheel bearing noises on the same axle.
If the channel 1 transmitter is listening to the left front wheel bearing and the channel 2 transmitter is monitoring the right front wheel bearing, you can compare the two noise signals, listening for evidence of abnormal grinding sounds, etc.
For example, if you suspect a wheel bearing problem, in addition to monitoring both front wheel bearings, you can attach a third transmitter to the transmission and a fourth to the differential.
Noises and vibrations tend to travel, and since the unaided human ear might suspect a wheel bearing, the noise may actually be coming from another source such as the transmission. Using this type of monitoring system helps you to pinpoint the area of concern.
This type of chassis ear can be used to monitor and diagnose a wide variety of noises and component operational condition, including (but not limited to) fuel injectors, alternator, wheel bearings, brake calipers, CV joints, springs, transmissions, differentials, shock absorbers, upper strut bearings, tie rods, ball joints, water pumps, power steering pumps, A/C compressors, body squeaks, etc. ■