It’s common for customers to gripe about various ride control concerns — vibrations, pulling, noises, etc. However, the customer’s description is often vague or misleading. Attempt to gather as much information from the customer as possible prior to performing an inspection. For example: ‘Do you only hear the funny noise when driving on bumpy roads, or on smooth roads as well?’ If you suspect the vehicle is heavily loaded with cargo at times, ask ‘Does the wandering you experience only occur when heavily loaded?’ 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.
Here are some examples of ride control complaints:
- The vehicle tends to pull/wander to the right.
- There’s a vibration when pressing on the brake pedal.
- There are noises that seem to be coming from underneath the vehicle as it travels down the road, or when the vehicle goes over bumps.
- The steering wheel vibrates at a certain speed. The customer may also feel that vibration in the seat.
- It seems harder to drive in a straight line, and the issue is getting worse as the vehicle ages and mileage increases.
Resist the temptation to diagnose any operational concern at the counter, based only on what the customer tells you. It’s imperative to perform a test drive and inspection to properly diagnose the complaint. Jumping to conclusions opens the door to misdiagnosis. For instance, based on what the vehicle owner describes, you may assume that a wheel alignment is all that’s needed, only to discover later that control arms bushings and lower ball joints require replacement, in addition to alignment. In short, don’t tell the customer what’s needed before performing a test drive and inspection.
VEHICLE PULLS IN ONE DIRECTION
Check the basics at the start of any ride control diagnosis by inspecting tire size and inflation, as well as ride height. This initial check can provide a verification starting point or can help to lead you in your diagnosis. Unequal tire inflation can easily lead to a directional pull.
After checking inflation, continue by looking at the tire size — specifically diameter — and verify that both tires on the same axle are the same size. If a previous tire replacement resulted in only one tire being replaced and it’s 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 will tend to pull to the left. Ideally, all tires should be the same make and model, and overall tire diameter should be the same on both sides of both the front and rear axle.
As noted earlier, improper tire inflation pressure is one of the leading causes for a directional pull. Depending on the sensitivity of the suspension design, as little as a 3-5 psi change per axle side can account for a slight 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/drift as well.
If the tire inflation pressures are correct and the vehicle still pulls, consider swapping left and right side tires. (If the tires are directional, this will require demounting, remounting and balancing). Internal tire construction may be different enough to result in a slight difference in belt reaction to road forces.
Checking vehicle ride height (and comparing your findings to factory specs) can help to quickly identify a potential spring fatigue or failure condition.
Wheel alignment angles 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 the side with more toe-out.
If camber angles differ from 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 a camber angle of negative 1 degree, while the right front wheel has 1.5 degree positive camber, the vehicle may pull or drift to the left.
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 towards the left.
Brake drag resulting from sticking calipers can cause both an accelerated brake pad and rotor wear issue as well as a directional pull. If the caliper pistons on one caliper do not retract fully (during non-braking or after braking), the pads can retain enough rotor contact to reduce the free-wheeling operation of the rotor and create a pull towards the side with the sticking caliper. Sticking/stubborn caliper pistons can be caused by corrosion in the piston bore as a result of moisture contamination, or following a brake pad replacement after the brake pads were severely worn. 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 or contamination building up in the unused area of the piston bore. Once the new pads are installed, the piston(s) can be further retracted while moving within a non-smooth area of the bore. This potentially results in the piston being slowed down or stuck in the contaminated bore area.
If everything seems to check out and you don’t find any obvious causes for the directional pull, consider how the vehicle’s cargo is distributed. If one side of the vehicle is excessively loaded as compared to the other side, this can affect the front wheel alignment angles with changes to toe and camber angles. Granted, the uneven loading would have to be rather severe, but it’s worth considering during the diagnosis.
VIBRATION AT SPEED
The vehicle may exhibit a vibration felt at certain speed ranges. This is usually an issue involving tire imbalance. Prior to weight-balancing the wheel, pay attention to tire mounting clock position. If the tire features a yellow dot on the sidewall, this indicates the lightest point of the tire. If the sidewall features only a yellow dot, mount the tire so that the yellow dot aligns with the air valve, which will be the heaviest point of the wheel (due to the weight of the valve stem and the TPMS sensor). If the tire features only a red dot, this indicates the tire’s highest radial point. This should be aligned with the wheel’s lowest point. The wheel may feature a reference mark or dimple to indicate the low point of the wheel. If the wheel features no such reference mark, align the red dot to the valve stem. If the tire features both a yellow and red dot, the red dot always takes priority. Aligning these tire dots to specific points of the wheel is referred to as match mounting. Due to the nature of tire construction, it’s nearly impossible to produce a tire that is perfectly balanced or perfectly round under dynamic conditions. These reference dots on the tire allow us to compensate for tire-to-wheel conditions and to help minimize the use of balancing weights.
Also consider how the specific wheels center onto the hubs. Some wheels feature slightly oversized center holes that don’t tightly register to the hubs, and rely on the interface of the wheel fastener holes to the wheel studs to achieve a centered wheel position. This is referred to as a “lugcentric” design. If the wheel centering takes place between the wheel center hole and hub, this is called a “hubcentric” design, as is common on many alloy wheels today. Be aware that some aftermarket alloy wheels are produced with oversized center holes to allow application to a variety of vehicles. In this case, the hub-centering (hubcentric) goal occurs with the addition of a centering spacer that fills the excess void in the wheel’s center hole and allows proper wheel centering to the hub. When servicing aftermarket alloy wheels, pay attention to this. If the complaint seems to indicate a radial runout issue, the centering spacer may be missing.
RADIAL FORCE VARIATION
If you’ve tried balancing, match-mounting, and have checked radial runout, but the customer still complains of periodic vibration, suspect a radial force variation occurrence of the tire when it’s in a loaded state (when the vehicle is driven). Radial force variation is so named because the radius of the tire varies according to vehicle speed and load. This is the “live” characteristic of the tire, where the tire may have “soft” spots and “stiff” spots in the carcass, tread or in the sidewall construction. Given the high quality control processes used by today’s tiremakers, it’s rare that a force variation problem will occur, but when it does, it can be a tricky demon to chase.
Even though no problems may be found as the tire rotates on the balancer, when the tire experiences a load, the transition of the harder and softer sections of the tire may create a series of harmonic vibrations as the tire contacts and leaves the road surface. Depending on the conditions, this harmonic may occur once per revolution of the tire, or it may occur in a series of vibrations per revolution. It’s possible that this phenomenon may vary according to changes in tire pressure, vehicle speed, individual tire load and the road surface conditions, all of which may serve to reduce and/or amplify the vibration problem. The use of a road force balancing machine can isolate this potential issue. While we don’t have the space here to delve deeply into RFV, our sister publication, Modern Tire Dealer, offers articles that address this subject in detail.
VIBRATION DURING BRAKING
If a vibration and brake pedal bounce occur during braking, the most likely cause is a warped brake rotor, which causes 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 as the result of careless/improper tightening of wheel fasteners. Many passenger cars today feature thin-hat rotors that are easily distorted if the wheel fasteners are unevenly or excessively tightened. This is why it’s important to make use of a calibrated torque wrench, 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, of course. Wheel nuts (or bolts) must be tightened in a crisscross pattern in order to equally spread the clamping force. Avoid tightening fasteners consecutively in a clockwise or counterclockwise pattern. When installing alloy wheels, especially when dealing with new wheels, be aware that the alloy material may experience slight compressive force when first tightened, and it may begin to relax after a number of miles, reducing clamping force. It’s always a good idea, after the first torque application, to check and re-torque after perhaps 50-100 miles of use.
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), and 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 0.05 of-an-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 of-an-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.
If, during initial inspection, you observe a discolored rotor, this is a sign of an overheat condition, which could be caused by several factors, the most likely of which is poor braking habits by the driver. The driver may have a habit of excessively riding the brake pedal and/or abusing the brakes by nailing the brake pedal at the last moment during stops instead of applying moderate pressure prior to final stopping. Or, the brake pads may be the wrong choice for the application, requiring excessive brake pedal pressure. Upgrading the pads to a more robust pad material may solve the issue. Of course, if the rotor is glazed and/or heat checked, the rotor(s) must be replaced as well. If the application involves an emergency vehicle, such as an ambulance or police vehicle, only heavy-duty, high performance pads (for instance, a ceramic metallic compound) that are designed for fade-free panic stopping should always be installed. In short, fit the pads to match the application.
A “noise” complaint has the potential to cover quite a lot of ground. Try to obtain more detailed information from the customer. What type of noise is heard? Clicking, groaning, grinding, popping, whirring, whistling, chirping, banging, etc. When is the noise heard? While starting the engine, or when cruising, braking or turning?
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. Worn or sticking shock absorbers may produce a squeaking sound when the driver enters the vehicle or during operation over uneven road surfaces.
A whirring, groaning or squealing noise may be heard due to a dry or worn power steering pump, or engine belt idler pulley. Squealing or chirping noises heard during engine startup, idling or upon initial acceleration may be indicative of loose, out of alignment or worn engine drive belts.
Loose, damaged or badly rusted exhaust system components can cause harmonic rattling or banging noises. This includes pipes, hangers, heat shields, etc.
Always check for worn suspension components. 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 mis-diagnosed 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 and make the vehicle owner concerned about a major problem. Worn or damaged lower control arm bushings can result in a slight clunking/banging noise during moderate acceleration or deceleration.
Naturally, a loud booming or unusually loud exhaust note is likely due to a leak in the exhaust system from a rusted-out or muffler, pipe, etc.
A ticking or clacking noise during engine startup and during warm-up may be caused by piston skirt clatter until the pistons expand at normal operating temperature. A dreaded deep knocking noise during engine operation is a sign of worn/damaged connecting rod bearings. A clattering noise during engine startup and idle that seems to be coming from the top of the engine is indicative of either poor oil delivery to the valvetrain or loose rocker arms, which, depending on engine design, may involve insufficient oil delivery to the top end (a clogged oil passage due to sludge and infrequent oil changes), worn cam followers, worn or out-of-sync camshaft phasers, etc. We won’t delve further into engine noises, since we’re concentrating on ride-related concerns in this article.
SHAKE AT SPEED
A “shake” complaint by the customer potentially covers quite a bit of ground. 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. Excessive vertical movement of the axle pinion may excessively change 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.
If by chance the vehicle is equipped with a manual transmission, ask the customer if a clutch job was recently performed, and if so, did the “shake” issue begin to occur after the clutch service. It is possible that the wrong clutch assembly was installed, or that an incorrect flywheel was installed. For example, if a zero-balanced flywheel was installed to an externally balanced crankshaft, or a flywheel with an offset balance was installed on an internally balanced crankshaft, an engine and subsequent driveline vibration is more than likely.
This may seem like a stretch, but also check for any body or chassis issues involving a component that is affected by oncoming air at highway speed, such as a front lower air diverter or rear airfoil/spoiler. If a component experiences forces inflicted by air pressure, and if that part is loose or damaged, this can cause the vehicle to experience a “flutter” as air speed increases.
Severely worn shock absorbers (independent shocks or strut dampers) prevent controlled vertical wheel travel, reducing correct tire-to-road surface contact pressure and 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 uncontrolled over-travel of the suspension and 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 worn/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.
Worn shocks/struts create a number of issues, including allowing the vehicle to be more susceptible to the force of wind gusts and crosswinds which require the driver to constantly correct the steering. Poor suspension dampening due to worn shocks/struts contribute to uneven tire wear and “cupping” which occurs as the tires are compressed and released repeatedly against the road surface. Braking distances are reduced because even though the brakes are trying to do their job, the reduction of suspension control allows body inertia to permit the body to keep moving forward. This places excessive stress and wear on front brakes and diminishes the effectiveness of the rear brakes due to body weight distribution. (As the rear of the body tries to lift upwards, it reduces rear tire grip, which results in longer stopping distances and premature front brake wear.)
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.
In addition to shock/strut damper issues, low tire pressure on one or both axles can easily cause a wandering effect — as the underinflated tire sidewalls are forced to flex excessively, resulting in a “loose” and sloppy steering control. Of course, under-inflation will also cause the tires to generate excessive heat, potentially leading to tire failure.
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 wheel bearings. Loose or worn wheel bearings will result in excessive lateral wheel play, and easily contribute to a sometimes twitchy wander issue.
If the vehicle is equipped with a trailer hitch, ask the customer if the wandering issue only takes place when towing. If so, the wander may be caused by too much tongue weight which changes the weight distribution of the vehicle, placing too much weight at the rear axle and reducing weight at the front axle. This transfer of weight balance lightens the front end, and reduces steering axle tire contact patches to the road surface, which causes the driver to constantly correct for straight line direction.
In addition, the trailer may be unevenly loaded, with the majority of the trailer weight towards the rear of the trailer. This can result in the “tail wagging the dog” syndrome. In a severe condition, this can result in a very dangerous and difficult to control condition at freeway speeds.