Auto Service Professional

JUN 2018

Magazine for the auto service professional

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42 A S P J u n e 2 018 C h a s s i s S e r v i c e 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 dif- ferent diameter, the smaller diameter tire will cause the vehicle to pull in the direction of the errant side. For instance, if the le front tire fea- tures a smaller diameter as compared to the right front tire, the vehicle would tend to pull to the le. 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 lead- ing 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. e pull will occur at the side that features the lower inflation pressure. e 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. Un- even rear tire inflation can cause a pull, as well. Wheel alignment angles due to suspension and/or steering component wear can have a pro- found effect on the vehicle's tendency to pull in one direction. is 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 le front wheel has nega- tive 1 degree of camber while the right front wheel has 1.5 degree positive camber, the vehi- cle will pull to the right. While the caster angle on many common vehicles may not be readily adjustable, uneven le/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 le front wheel has a caster angle of 0.5 degree positive and the right front wheel has a caster angle of 2 de- grees, the vehicle will pull toward the le. 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 aer a brak- ing), 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 Electronic listening devices such as Steelman's Wireless ChassisEAR can help to pinpoint noises and vibrations in a more quantitative manner than human senses. Worn or damaged upper strut bearings, regardless of upper hat/bearing design, will generate a grinding or popping noise when the wheels turn and can cause constant or intermittent steering wheel return issues.

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