2010 Mazda 6 Suspension/Steering Issue Diagnosis

Sounds like you know a lot more about suspension and alignment than most people. I'm not familiar with your specific model but to start with I can offer some generalizations that I found to hold true on 99 percent of front-wheel-drive cars.

First of all, you're getting too picky about the height difference. To me ride height is extremely critical in preventing tire wear and poor handling and braking but 1/4" difference side-to-side is well within acceptable tolerances. It's the height that's important, not the difference, and the height is strictly a result of the springs. Springs don't get damaged in a crash. They get weak with age and allow the car to sag. That changes the geometry of the steering and suspension systems.

The next thing is caster. That angle has very little affect on tire wear. On older rear-whee-drive cars and trucks it had to be nearly equal on both sides. When you let go of the steering wheel, if everything else is equal, the car will pull toward the wheel with the lower caster. On front-wheel-drive cars for some reason that is not the case. I've crash-repaired cars with as high as 3.0 degrees difference in caster, with no obvious cause after a second check on the frame machine, and the car drove perfectly. There are a few models that are not tolerant of mismatched caster and on those caster will be adjustable. Caster is not adjustable on most front-wheel-drive cars. Caster is one of the angles that can not be measured directly on any alignment computer. The wheels need to be turned left, then right, and camber readings are taken, then from them the computer calculates caster for each wheel. It's not uncommon to get different caster readings between two different mechanics or two different setups on the alignment rack. Caster is also greatly affected by the amount of weight in the trunk or in the car itself so to get two different readings on two different days is not uncommon.

Caster is the main angle affecting directional stability and steering wheel return. Higher caster makes the steering wheel harder to turn, it will make it snap back faster after a turn, and the car will have less tendency to wander.

Camber must be correct for proper tire wear but it also must be nearly equal on both sides. If all else is equal, the car will pull toward the higher camber wheel.

I can start you out with a couple of observations. The slow or incomplete steering wheel return can be the result of caster being too low, or it can be caused by not torquing replacement ball joints to proper specs. The ball joint torque is more of a large truck thing. Next, if you have a camber pull, especially if you say camber is not adjustable, that difference side-to-side can be offset by adjusting in a caster pull the other way. The two will counteract each other and the car will go straight, ... Most of the time, but that will set up an unstable condition when you go over bumps in the road. You will typically notice the steering wheel shift a little one way when the car body goes up and the other way when it comes back down. That is a miserable car to drive.

A bent strut is usually easy to spot by the cracked and flaked-off paint but the clue is camber is off a lot before any parts are replaced. You also have to look at "steering axis inclination" (SAI). A bent control arm will change SAI AND camber. Readjusting camber will fix camber but not SAI. (Almost all cars can have camber made adjustable). I have to post this reply before the web site kicks me off. I'll look at the alignment numbers next. Basically, there never is a spec. For SAI. All that is important is it is the same on both sides within 0.2 degrees. A typical value is around 26 to 32 degrees. If it is not equal the first thing to look for is bent control arms, ... Anything that moves the location of the lower ball joint and the upper steering pivot which is an upper ball joint or strut mount. If those two steering pivots are in the right spots, SAI will be equal, then if camber is wrong it is strictly an adjustment issue or a bent strut.

Now that you have any parts replaced that might have been bent, if SAI is not equal, look at the cross member or body sheet metal the lower control arms are bolted to. If the cross member is bolted to the car, those bolts can be loosened and a pry bar is used to shove it back until SAI is equal. On some cars the cross member is welded in place and you have to find bent parts to correct SAI.

SAI usually doesn't have a specification, but regardless, I have never seen it this low on any vehicle. The difference side-to-side is a little more than we would like to see but I don't think that would be enough to cause handling issues.

Looking at the first printout, under the current readings, there's a 1.0 degree camber pull to the left. That's a bunch and I'd be looking for a way to correct that.

If you stand in front of the car and look back at the lower and upper ball joints, the two steering pivots, and draw an imaginary line through them, that is steering axis inclination, or the SAI angle, compared to vertical. The left is lower meaning that line is closer to true vertical than the right side. The upper ball joint and control arm would have to be pulled out, which isn't likely to happen, or the lower control arm would have to be pushed in or bent to collapse it. That would be the typical result of hitting something. If the strut was bent that would not change the location of the ball joints, so SAI wouldn't be affected, but the spindle would tip so camber WOULD be affected.

If we are to assume the SAI is okay, that would say the two ball joints are in the right places so the two control arms would have to be okay. I'm trying to picture your suspension design. If you have an upper control arm and ball joint, the spindle is between the two ball joints and is not bolted to the strut. Chrysler used that design in the '90s. The strut is a giant shock absorber that is strong enough to hold the coil spring which holds the car up, but it isn't involved in any alignment angles.

On the Chryslers the upper control arm was adjustable and pretty easy to move around. Check if that can be moved on your car. I was going to suggest a bent spindle, but if the upper control arm can be slid in about 1/4", that would increase SAI to bring it closer the the right wheel, and it would lower left camber and get that back where it should be.

Note that I'm leaving tomorrow for the nation's second largest old car show swap meet so you won't hear from me for a few days. I'll check back when I get home Sunday night.