Finding Hidden Suspension Damage

Jan. 1, 2020

Why should a shop wait until the end of repairs to discover a suspension part needs to be replaced or that the vehicle has to return to the frame machine? Understanding diagnostic suspension angles makes finding damage that regular wheel alignment te

By Fred Dehn and Iva Dehn
Contributing EditorsSuspension angles are nothing more than measurements that any technician can use on a daily basis to speed repairs by finding damaged parts and misaligned suspension areas before they become rework.In order to check these areas and uncover problems, the repair technician must be prepared to look at 10 suspension angles-seven at the front and the other three at the rear of the vehicle. These measurements can be checked during the early stages of repairs, either by a computer or a mechanical system, to eliminate costly repair delays when the vehicle's wheels do not line up after the repair is completed.The first thing to remember: It really doesn't matter what brand, what year, how big or how small. Every vehicle still carries these 10 angles/measurements. Each one affects how the vehicle will handle when it is finally put back on the road.The first three measurements are the ones everyone has heard about for years:Front Camber-All vehicles have this tire wear angle. But there is one thing about camber that every technician should know: Not one car or truck in the shop has a camber adjustment. There is, however, a camber reading.Camber is measured in degrees and is considered zero if the tire is sitting straight up, or true vertical. When the top of the tire leans toward the center of the vehicle, it is negative. As it leans away from the centerline, it is positive.An out-of-specifications reading should be treated as a symptom of something wrong. Never try to fix a camber problem by considering only a symptom. If camber needs to be repaired it can only be changed by moving the steering axis inclination (SAI) angle or the included angle, which we will address later.Caster-This angle is a directional control angle and not necessarily a tire wear angle. It should be viewed from the side of the tire. Zero caster is present when the top pivot point-upper strut pivot or upper ball joint-is directly above the bottom pivot point. When the top pivot point moves rearward-toward the driver-it is measured in degrees and is called positive. If it moves forward, it is called negative. If you have a caster problem, you are only looking for something that would cause a forward or backward movement.Front Toe-This is the most severe tire wear angle of all. It must be set correctly. Toe-in is positive, and toe-out is negative.This is a brief synopsis of wheel alignment basics. To locate hidden suspension damage, you must turn to the valuable information that can be found in the other "forgotten" angles.SAIThis is a directional control angle, and no diagnosis can begin without it. It is a factory adjustable angle on some vehicles. Any time the upper or lower pivot point is moved toward or away from the center line of the vehicle, SAI is being adjusted. There are many vehicles with "in" or "out" SAI adjusters at the top of the strut tower or "in" and "out" adjustment at the lower pivot point.Let's say we are working on a late model Ford Taurus. The camber specification is -1/2.The reading from the right front wheel is 1