Ever take a long trip in a vehicle with a steering pull problem? Having to maintain constant pressure on the steering wheel can very tiring, not to mention hard on the tires. A vehicle with a pull problem is a vehicle that is fighting the forces of nature. Something is amiss and is causing the vehicle to follow a path other than a straight one.
There are actually several different types of steering pull: a steady pull, a pull that only occurs after turning (memory steer), or a pull that only occurs under certain driving conditions such as bump steer or torque steer.
An off-center steering wheel may or may not accompany a pull (which we'll cover shortly). Other times the pull may be more of a "drift" or steering wander to one side or the other. So let's look at some of the common pull-related conditions along with their causes and what you have to do to eliminate them.
This is a condition where the vehicle continually pulls or drifts to one side while traveling straight. The driver typically has to maintain steady pressure on the steering wheel to keep the vehicle on the road. Possible causes include:
Uneven camber side-to-side. Too much cross-camber can make a vehicle pull or lead towards the side that has the most (positive) camber or away from the side that has the least (negative) camber. The underlying cause may be a bent strut or mislocated strut tower, a bent spindle, collapsed control arm bushing, weak or broken spring, or a shifted crossmember or engine cradle. Check SAI and the included angle to see if these are in or out of specs to diagnose the problem. Also check ride height. Correct by replacing worn or damaged parts, correcting location of strut tower, repositioning engine cradle, and/or reducing cross-camber to half a degree or less by readjusting camber to specifications.
Uneven caster side-to-side. Too much cross-caster can make a vehicle pull or lead towards the side that has the least (negative) caster. The underlying cause may be a bent strut, spindle or mislocated strut tower. Correct by replacing damaged part, correcting location of strut tower, and/or reducing cross-caster to half a degree or less by resetting caster to specifications.
Rear axle steer. The front wheels are with alignment specifications but the vehicle pulls to one side. The underlying cause may be rear toe out of specifications, a bent rear axle, chassis misalignment or a stackup of assembly tolerances in the chassis causing rear axle misalignment. Measure and compare the wheelbase on both sides, check for the presence of a thrust angle, and/or measure individual rear toe. Correct by realigning the rear axle or rear toe, or by performing a thrust angle alignment.
Brake drag. The pull is constant to one side and may get worse with the application of the brakes. Raise the vehicle and spin each wheel by hand to check for excessive drag. Possible causes include caliper sticking, frozen or sticking piston in caliper, overfilled fluid reservoir in master cylinder (does not allow caliper pistons to retract when brakes are released), weak drum brake return springs, misadjusted drum brakes, misadjusted parking brake, misadjusted parking brake pedal switch (creates residual pressure in the master cylinder to cause drag). Readjust or repair brakes as required.
NOTE: If the pull only occurs when the brakes are applied, the problem may be unequal braking not a dragging caliper or misalignment. The vehicle will pull towards the side with the stronger front brake and away from the side with the weaker or inoperative front brake. Uneven braking can be caused by a sticking floating caliper, a frozen caliper piston, the use of different grades or brands of brake linings side-to-side, fluid leaks, or contaminated linings on one side (by brake fluid or grease). Correct by repairing brakes as required. Other causes may include worn or loose control arm bushings or strut rod bushings that allow alignment changes when braking, so be sure to inspect these components before blaming the brakes.
Low tire pressure. The vehicle will lead towards the side with low pressure in the front tire. Correct by inflating tires to recommended pressure.
Mismatched tires side-to-side. The vehicle will pull or lead towards the side that offers the greatest rolling resistance. Compare tire sizes, tread wear, tread styles and patterns, also brands.
Uneven tire wear. If one side of the tread is worn more than the other, the tire develops conicity. The effect is much the same as camber, causing the tire to roll towards the side which is worn most. The uneven wear may be the result of incorrect camber, toe and/or failure to rotate the tires periodically to even out wear. If rotating the tires side-to-side reverses the direction of the pull, the tires need to be replaced.
Ply steer. A manufacturing defect in the way the belts are positioned inside the tire causes the tire to generate a lateral (sideways) force as the tire rolls. To test for this condition, drive the vehicle forward, then in reverse. If the direction of the drift or pull changes, one or more tires at at fault. Rotating the tires front-to-rear or crosswise may help cancel out the ply steer, otherwise tire replacement is necessary to correct the condition.
Unbalanced power assist. Seal leaks in the control valve or off-center steering may route hydraulic pressure into one side or the other of the boost cylinder piston causing the steering to want to turn itself to one side. This can be checked by raising the wheels with the engine running to see if the wheels turn to one side by themselves. No change would indicate another cause, but if the pull suddenly vanishes an imbalance in the power steering system is to blame. The control valve assembly or steering gear needs to be replaced.
Excessive road crown. Roads are raised or crowned in the middle so rain water will run off to the outside for proper drainage. But the slight slope to the pavement can often make a vehicle drift to the outside. This can be countered by adding a little positive camber and/or negative caster to the left front wheel , but this should only be done if the vehicle spends most of its time on crowned roads and you have a noticeable pull.
MEMORY STEERThe steering wheel and wheels want to return to some position other than center. This may cause a steering pull or drift to one side after turning. Possible causes include:
Misalignment or improper installation of Ford rubber bonded socket (RBS) tie rod ends. RBS tie rod ends do not swivel freely like conventional tie rod ends. When installed, the steering linkage must be centered and straight ahead before the tie rod studs are tightened. Inspect and readjust as needed.
Binding in upper strut mounts. Raise wheels and turn the steering from side to side. If effort is high, disconnect tie rod ends from steering arms and turn each wheel by hand to check for resistance. If upper strut mount is binding or loose, the strut will have to removed or rebuilt to replace the upper bearing plate assembly.
Binding in steering gear or linkage. Inspect tie rod ends and sockets. Check idler arm bushing. Check rack yoke adjustment or steering play in steering box. Replace or adjust as needed.
Binding in ball joints. Unload the ball joints by raising the suspension. Let the suspension hang free with MacPherson struts. Support the lower control arm on an SLA, modified strut or wishbone suspension if the spring is on the lower arm, or the upper arm if the spring is over the upper arm). Turn the wheels from side to side to check steering effort. If high, disconnect the tie rod ends and try again. If a ball joint is binding, replacement is required.
Unbalanced power assist. Seal leaks in the control valve or off-center steering may route hydraulic pressure into one side or the other of the boost cylinder piston causing the steering to want to turn itself to one side. This can be checked by raising the wheels with the engine running. If the steering goes to one side all by itself, the control valve assembly or steering gear needs to be replaced.
OFF-CENTER STEERING WHEELThis condition may accompany a steady pull or memory steer. But if the steering wheel is off-center (crooked) but there is no pull to either side, possible causes include:
Steering linkage not centered when toe was adjusted. Correct by recentering steering wheel and equalizing lengths of both tie rods, then readjusting toe to specifications.
Bent steering arm or linkage. Check turning angle both ways. If arm is bent, knuckle (or strut if arm is attached to strut) will have to be replaced.
The vehicle lacks directional stability and wanders or drifts from side to side. Possible causes include:
Loose or worn steering components. Inspect the tie rod ends, inner tie rod sockets on rack & pinion steering units, and the idler arm and center link on parallelogram steering. Check the steering column couplings. Also check for loose or broken rack mounts. Check the amount of play in the steering rack or steering gear. Lateral play at the edge of the steering wheel should usually be less than 1/4 inch (always refer to manufacturer specifications). Replace worn parts and/or adjust rack yoke or adjustment screw on steering box to reduce play.
Loose or improperly adjusted wheel bearings. Check and adjust wheel bearings to specifications.
Insufficient caster. This may be due to increased ride height at the rear of the vehicle (raising the rear end with air shocks or air springs) or lowered ride height at the front of the vehicle (weak springs or shorter than stock springs). Increase caster and/or reset to specifications.
Extremely low tire pressure. Inflate to recommended pressure.
Extreme toe misalignment. Check the steering linkage and adjust or repair as needed.
The steering suddenly jerks or veers to one side or the other when the vehicle passes over a bump. The condition is caused by unequal toe changes that occur as the suspension travels through jounce and rebound. The condition can be confirmed by checking individual front toe with the suspension loaded (compressed), then checking toe again with the suspension raised slightly. If the amount of toe change is not equal on both front wheels, it can cause a momentary pull to one side. The direction of the pull will depend on which end is high or low, and whether the steering linkage is ahead or behind the knuckle.
Possible causes include:
Parallelogram steering linkage not level. Check the idler arm height, and adjust as required.
Steering rack not level. Check rack height and rack mounts. Repair, adjust or replace as needed.
Bent steering arms. Check to see that both are the same height. Replace knuckle (or strut if arms are mounted on strut) if bent to correct.
Structural damage such as frame twist, mislocated or twisted crossmember or engine cradle.
Not centering the steering linkage before adjusting toe. This can result in unequal toe changes when the suspension moves up and down.
The steering veers or pulls to one side during hard acceleration. This is a common condition in front-wheel drive cars with unequal length driveshafts, and is caused by unequal toe changes as the suspension is loaded. Compliance allows the wheel with the longer driveshaft to experience less toe-in change than the wheel with the shorter driveshaft. This causes the vehicle to veer towards the side with the longer driveshaft. FWD cars with equal length driveshafts usually do not experience this condition.
Torque steer cannot be eliminated, but certain conditions may make it worse:
Loose or collapsed control arm bushings.
Loose or worn tie rod ends.
Loose or worn inner tie rod sockets.
Loose or broken engine/transaxle mounts.
Vehicle manufacturers have offered various repairs to reduce the severity of torque steer in some FWD cars. The corrective measures include using stiffer control arm bushings, shimming motor mounts, realigning the engine cradle, replacing the motor mounts with stiffer mounts, or increasing cross-camber.
Wheel Alignment Guide (click for details)
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Getting The Right Attitude: Restoring Ride Height
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