Steering and Suspension
Contents
1. By KARL SEYFERT Regardless of the materials used friction and gravity inevitably cause wear that degrades steering and suspension performance on all vehicles even those constructed of unobtanium t s no longer considered rare or unusual for a vehicle to travel 100 000 miles or more and still have all of its original steering and suspension components This extended wear trend in cludes other areas of the vehicle as well Engines last longer transmissions last longer everything lasts longer Better cars Better roads Better maintenance We may disagree on why this is true but at least we can probably agree that it is true N one of these parts is the same af ter 100 000 miles as it was at 0 miles of course In the case of steering and suspension parts the deterioration is gradual and it may be difficult for the driver to notice anything has changed until things have gotten bad enough to represent a safety hazard Rather than waiting until then it s best to take a proactive approach 34 MOTOR June 2005 Why wait until the vehicle comes in behind a tow truck to start thinking about steering and suspension wear Road Test Begin with a road test If the customer is available take him along or have him drive to get a feel for the vehicle Use your eyes ears and the seat of your pants as you drive Do you hear any unusual noises D oes the vehicle seem to bob and weave as it passes over ir regularit2. select a street and time when there are no cars immediately behind you To test both the front and rear shocks brake hard from a speed of 25 to 35 mph but not hard enough to lock the wheels H old firm pressure on the pedal all the way through to a com plete stop If you dont feel a jolt at the end of the maneuver repeat the test and don t ease off the brakes until you feel it Driving repeatedly over a bumpy stretch of road is also a good way to check for shock absorber fade resistance The same inertial weight transfer that jerks your head at the end of those hard stops will also compress the springs sufficiently to reveal a weak shock The nose of the vehicle should sink rise and center while the tail should mirror its motions Any further bobbing motions indicate a weak shock If either the front or rear fails to center effectively one of the June 2005 MOTOR 35 STEERING amp SUSPENSION WHERE IS THE WEAR shocks may be sticking Similarly if the vehicle bobs its front or rear more than once the shocks need replacing Visual Inspection After the road test get the vehicle on a lift and conduct a thorough steering and suspension inspection If you sus pect a steering or suspension related pull check the components as you would during a prealignment inspec tion Be on the lookout for loose parts Which joint is the load bearing joint This multilink Cadillac front suspension and any indication o
3. and to make sure they re still there A missing suspension stop can cause a great deal of noise over a steep driveway apron or a deep pothole Lube all steering stops as part of every rou tine undercar service t s easy to misdiagnose the cause of a clunk In many cas es a worn or damaged bushing gets overlooked in the rush to replace a more expensive component Careful inspection of the entire suspension system in both the loaded and un loaded positions is required for the kind of accurate diagnosis your customers deserve M ost stabilizer bar mounting bushings can be correctly di agnosed only with the vehicle s weight on its wheels When inspecting stabilizer bar links both sides of the vehicle must be equally supported with the weight on the wheels Other wise the torsion of the bar will load both links hiding any play M ost control arm bushings can be checked only with the wheels hanging or otherwise unloaded M Visit www motor comto download a free copy of this article June 2005 MOTOR 41
4. not fully return to center E xcess friction in the steering or suspension system keeps the steering from returning to center following a turn Worn strut mounts can cause this friction If they re badly worn the suspension spring can actually wind up as the soring turns and the strut mount remains stationary If this happens the steering may want to return to the direction the wheel was last turned to even after you manually return the steering wheel to center Improper steering and or suspen sion part replacement techniques and or tightening proce dures can also cause memory steer because the bushing rub ber tries to return to its neutral position Worn or broken springs are a suspension problem that s 40 MOTOR June 2005 On trucks and other vehicles with so called convention al leaf spring rear suspensions noise can develop due to broken spring leafs or damaged shocks Worn bush ings can allow lateral suspension movement and the ve hicle may seem to steer from the rear difficult to ignore unless the driver is completely oblivious If one end of the vehicle sits noticeably lower than the other or if the ride height is uneven from side to side worn springs are almost certainly to blame M easure the chassis height and compare it to specifications If the height is below the mini mum or poor ride quality or handling problems were noted during the road test spring replacement is certainly neces sary The spring is a
5. out Problems will occur if there s a difference between the two This can happen with bent front sus pension components wheels with dif ferent offsets or missing spacers on an aftermarket wheel Shocks When they aren t being ignored shock absorbers are often replaced in an at tempt to correct a condition that doesn t need correcting A light film of oil on the upper portion of the shock absorber tube or body is acceptable H owever a shock absorber dripping fluid is a sign of leakage and the unit should be re placed Just make sure the leak is not coming from another part Shock ab sorbers do not support suspension loads Don t replace shocks to correct vehicle sag that s a job for the springs The basic function of the shock ab sorber is to serve as a damping device for the spring or torsion bar suspension Shocks keep the wheels in contact with the road surface under all road and load conditions They also keep the springs from oscillating freely after the wheels roll over road irregularities Damping forces should be equal on each side of the vehicle Some vehicles are equipped with gas charged shocks Their sealed gas pressure resists expansion and com pression Some common indications of shock absorber failure are steering or handling difficulty uneven braking abnormal tire wear especially cupping springs bot toming out excessive bouncing after stops worn steering and suspension components and noise c
6. aused by loose shock absorber attaching parts A worn strut mount the red area in the illustration can produce noise as well as steering pull and memory steer problems Strut mounts should be carefully inspected and replaced if necessary during spring or strut service The shock absorber action should be smooth and uniform throughout each stroke To check the shock on the vehi cle support the lower control arm or stration courtesy University of Toyota Toyota Motor Sales USA This Ford Fusion axle and remove the shock s lower at tachment Grasp the shock absorber body and stroke it up and down as far as possible Many late model vehicles have multilink independent rear suspensions These de signs provide superior road holding along with a comfortable ride The multitude of bushings and joints can make a noise or handling diagnosis a challenge however 38 MOTOR June 2005 Photo courtesy Ford Motor Co front suspension combines a strut with upper and lower control arms and a pair of ball joints The bottom of the strut is attached to the lower control arm not the knuckle Unlike a conventional McPherson strut suspension it has no suspension locating duties To bench test a shock absorber po sition it in the same direction it s in stalled in the vehicle then extend it fully Next turn it upside down and fully compress it Repeat several times Replace the shock absorber if there s a lag or s
7. f moving compo nents such as loose control arm bolts Clean areas or scraped paint around bolts and nuts can indicate that some thing that isn t supposed to is moving around Anything that allows the wheels to point where they re not sup posed to while braking can cause a pull Loose components can also pro duce a single clunk noise when the brakes are applied and the vehicle weight shifts J makes sure the tires remain perpendicular to the road regardless of load or road Proper testing methods are required to identify worn components At the other end of the price spectrum this Toyota Echo uses a simple i ii McPherson strut front suspension The single lower control arm and ball joint locate the suspension at the bottom Is it a load bearing joint 36 MOTOR June 2005 Photo courtesy General Motors Photo courtesy University of Toyota Toyota Motor Sales USA While misaligned wheels will often cause a constant pull braking can ag gravate a slight pull An uneven scrub radius can cause a severe pull under braking A zero scrub radius will have little effect on steering pull if one front brake works harder than the other A positive scrub radius will pull very hard while a negative scrub radius will have aminimal effect M ost front drive vehicles have a zero or negative scrub radius to counteract the effects of torque steer If the scrub radii of both front wheels are near equal they ll cancel each other
8. ies in the pavement D oes it feel like anything unusual is going on under the vehicle As steering parts wear they cause the steering to become vague and un responsive When suspension parts like ball joints and control arm bush ings wear they cause unfamiliar clunks and bumps as well as uneven tire wear Loose or worn steering or sus pension components can also cause a Photo Karl Seyfert pull that occurs abruptly when the ve hicle hits a bump A steering wheel that changes positions during straight ahead driving after braking is a tip off that something is loose in the suspen sion or steering causing a sudden toe change M any techs still attempt to check the shocks and struts using the time honored bounce test Each end of the vehicle is manually bounced up and down then released The theory is that a worn shock or strut will allow too many oscillations before the bouncing stops What s never been established is how hard the suspension should be bounced how many oscillations are too many and how many are just enough You can use the vehicle s weight instead of your own to con duct a shock absorber test during your road test First drive up a gentle grade at 25 to 35 mph Uneven pavement is actu ally an advantage here Watch the rearview mirror as you drive If the rear end of the vehicle seems to float or bobble over the bumps that s a tip off that the rear shocks need attention N ext
9. kip near the midstroke as the shaft changes direction the shaft seizes at any point in its travel except at the ends any noise other than a swish or click is heard when the stroke Is re versed rapidly any leaks are observed or the action remains erratic after purging air Struts amp Springs The strut shaft is a structural suspen sion member that takes the place of the upper control arm bushings and upper ball joint The strut shaft is also the shock absorber shaft so it must be able to handle both vertical and hori zontal loads Strut inspection should begin with a road test As with shock diagnosis be on the lookout for abnormal handling deteriorated ride quality vibration or Illustration courtesy Ford Motor Co any of the other symptoms already mentioned during accel eration braking and cornering Back in the shop bounce the vehicle while checking for binding that may indicate a bent strut shaft Inspect the strut for leaks or poor damping Poor damping is an indication of worn strut valving or lost strut fluid The top strut mount con tains a bearing that carries the vehicle load Check it for bind ing or roughness while steering from left to right with the tires on the ground Worn upper strut mounts can cause memory steer The ve hicle s designed in caster should cause the steering wheel to self center after a turn But if there s too much resistance to the caster s centering force the steering may
10. laced on a lift and the wheels are allowed to hang free If the ball joints are checked for wear in this abnormal position the chances are very good that significant wear will be missed leading to an Incorrect diagnosis The vehicle service manual will provide you with the proper diagnostic procedure to check ball joint wear As an example on a coil spring front suspension if the spring rests on the lower control arm it will be necessary to unload the suspension to test the lower ball joint To accomplish this raise the vehicle by placing a jack under the lower control arm as close to the ball joint as possible This gives you the maximum amount of leverage against the spring The ball joint is unloaded when the bump stop is not in contact with the control arm or frame Grab the tire at the top and bottom then rock it to check for loose wheel bearings A pry bar can also be placed between the bot tom of the tire and the ground to rock the tire A dial indi cator is then used to measure radial and axial ball joint wear If the upper ball joint is the loaded joint other methods must be used to allow the joint to rest in its nor mal position but with the load removed before checking for wear Worn or damaged ball joints should be replaced and they should always be installed in pairs regardless of whether both are worn an unequal amount While you re conducting your ball joint test inspect the bump stops and steering stops for damage
11. n integral part of the strut so strut disas sembly will be necessary to replace the spring To maintain consistent side to side ride height always re place strut springs in pairs M ake sure the replacement springs are an accurate match with the originals and correctly match the owner s intended use for the vehicle A replace ment spring set that s marketed as heavy duty would be a poor match for a customer who is more concerned with a smooth ride than with extra carrying capacity Bushings amp Ball Joints Inspect the suspension components in both loaded and un loaded positions A loose stabilizer bar mount bushing for example may appear normal when the wheels are hanging in the air on a lift but the play may be readily detectable with the vehicle resting on the ground Likewise many ball joints will reveal excessive wear only when loaded while the load must be removed from others for proper inspection Some ball joints have built in wear indicators that give you a visual indication of the amount of wear that has occurred This simplifies diagnosis but the vast majority of ball joints unfortunately do not have this feature To check them a proper ball joint test must be conducted Depending on suspension design ball joints are either loaded or unloaded when the vehicle is in its normal posi tion with all four wheels resting on the ground Things Photo courtesy Ford Motor Co tend to change when the vehicle is p
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