Put your hammer down and come to the rear straight axle with me. Let’s check it for wheel set back. We’re not positive what exactly happened in the wreck or prior to the wreck, for that matter. Did the vehicle run off the road?
Set Up for Set Back
When checking wheel set back, the first thing I do is check my wheelbase measurement for the vehicle I’m working on. I do this because it tells me if wheel set back is supposed to exist in the vehicle I’m repairing. This is rare, but you sure don’t want to remove any set back if it was built into the vehicle, so always check your wheelbase spec to see if it’s supposed to be the same, right to left.
Kind of fun, wasn’t it? (OK, OK, maybe I have a strange sense of satisfaction.) But measuring for wheel set back is an important step in delivering a complete and timely repair job to your customers. Give it a try in your shop, and your techs will be sure to find their own sense of satisfaction in a job well-done.
Measuring for wheel set back is one such geometrical element of the undercarriage that intrigues me. It’s also affords me a valuable opportunity to find additional damage and correctly repair the vehicle – something your technicians can achieve if they just start thinking outside the box.
Front set back is a measurement referencing a vehicle’s front wheels to a line running perpendicular to the vehicle centerline and parallel to a line drawn through the centers of the spindle. If a vehicle has front set back, one front tire/wheel assembly sits farther back from this imaginary reference line than the other. Positive set back indicates that the right front wheel is set back further than the left. Negative set back indicates the left front wheel is further back than the right. Front set back can be checked during a normal alignment and is used to diagnose collision damage or cradle misadjustment. If the cradle is adjusted incorrectly or damage is present, it’s not unusual to also see a reduced positive caster reading on the side with set back. Excessive set back can cause an alignment pull to the side with set back.