Drivers across this nation’s Snow Belt are using curbs to slow them down when the bald tires or last-minute brake smash do not. These repairs can be nice for improving cycle time averages and revenue — if you catch all the damage early on in the repair.
My preference on this type of damage is to get the car on an alignment rack and inspect for obviously bent parts. If there is nothing visible beyond a damaged wheel and poor steering, the alignment machine gives you a perfect opportunity to take a few measurements and pick up items that are not so easy to see.
Let’s look into some measurements that will help you spot problems before going to the trouble to set up your frame machine. (Keep in mind that I am a mechanical guy who does quite a bit of work for collision shops.)
The front-end inspection
Starting with the vehicle on its tires, have an assistant move just the freeplay in steering system and identify anything moving within the steering system before the wheels begin to turn. Don’t forget to look at the steering coupler as a possible place for movement when you are inspecting tie rods, center links, idler arms, Pitman arms and steering gear. You may identify some customer pay work beyond the accident, but you have to note and address everything or you will not get good results from your final alignment.
Once you have the freeplay wear identified, have your assistant move the steering so that the wheels are turning a little each way. Carefully inspect steering components that looked good before to make sure they are OK with the additional load of turning the tires. Keep in mind we are doing this with the vehicle on the wheels.
Inspect all of the control arm bushings, strut mounts and connecting hardware. If you identify any noises or squeaks, use a stethoscope to pinpoint the noisy component.
Ball joints are a very important part of an inspection, but you have to inspect and test them according to manufacturer’s procedure. It is no longer viable to tilt the tire at the 6 and 12 o’clock positions and call that a ball joint inspection: Many late-model vehicles have deflection specs less than 1mm on lower joints, and even less on upper joints.
Hub and strut considerations
One common problem with curb hits or objects striking a wheel is damage to the hub or hub bearing, resulting in a looseness in the bearing, noise in the bearing or runout in the hub unit. Often it is necessary to remove the wheel and measure runout on the hub with a magnetic or clamp-on micrometer. Here again, don’t guess — there are specs for these items.
On strut cars, unless there is a significant change in the static camber it may be hard to visually inspect them. The most common damage is the shaft or strut mount getting damaged. Sometimes moving the wheel through its turning arc will show you a bent strut as the strut binds or makes an unnatural arc through the travel, but the best way to catch a bent strut is with the alignment machine.
What we are looking for is that the camber on each side is pretty close to equal. If you have a radical difference side to side, you may have a strut damaged.
This condition is certainly not exclusive to bent struts. If you see that the total camber is pretty close to spec, but both sides are not equal, look for a possible problem with a bolt in X or K member having moved under the car on impact. This type of problem is generally indicated by being close to correct total camber — but both sides are off by a similar amount, with one side being more negative and the other side being more positive. Many alignment machines have K member alignment procedures to dial this back in for you.
This is where it is important to inspect each of the suspension pick-up points for damage or bent mounts prior to going through the procedure. This is a problem we see quite often, and even if the car is “in the green,” it will not track as well as it should or have good tire wear if this is not addressed. This problem can also occur on the rear of some cars where bolt-in cross-members are used.
Using SAI
Alignment equipment has a useful additional angle that can be used as a diagnostic angle, known as steering axis inclination, or SAI. Many vehicles do not have specs for SAI, but we can still use it to compare side-to-side measurements and locate problems with steering knuckles or damaged parts we might not have seen.
SAI is the measurement of the angle of the steering pivot line. Simply put, SAI causes some lift in the front of the vehicle when the wheels are turned and uses the weight of the vehicle to return the wheels to center (and you thought caster was the only stabilizing angle). If a vehicle is sluggish returning and all of the other angles look good, you’d better measure SAI. In fact, check it whenever you have a wheel contact something.
By now, you have done a very thorough inspection of the front steering and most of the suspension components. If this is a more extensive accident, there are other things to inspect, but I am guessing that there will be other damage that will have to be addressed before you are able to employ my alignment machine approach.
SIDEBAR: Bringing the noise
I want to offer a couple of other items that make my collision friends crazy: noises and vibration.
Vibration: Often in a curb hit, you have 1,000 lbs. of drivetrain with a lot of inertia sitting on rubber mounts. If a suspension cradle can move, doesn’t it make sense that drivetrain mounts can, too? Be sure to inspect the mounts for damage, and if you have to move a cradle or replace a mount, don’t be surprised if there is a buzz or vibration afterward on front wheel drive cars. Many carmakers have procedures for loosening up the mounts and settling the whole drivetrain to resolve these problems. You will find that Honda, Ford and Saturn all have a procedure when you replace mounts to remove bind in them. Vibrations can also be caused by missed wheel weights that came off, broken cords in tires that have hit curbs or potholes, or hidden damage to wheel bearings.
Noise: Let’s face it, we work in a noisy world and most of our customers don’t — so we have to be extra aware of noises when we are doing suspension repair. Those clunks, knocks and rattles can really irritate customers, but can be hard to track down.
Noises that are of the rattle variety generally are not caused by a loaded part like a control arm, steering component or ball joint, where clunks and knocks are more common. Suspension rattles are generally from a component like a sway bar link (particularly the type that bolt to the strut, and then the sway bar) and inside the strut itself. We have found that many of the strut type sway bar links will rattle if they are installed with an impact — and are another item that happens to be overlooked or damaged during service. Using a hex key to hold the stud while hand tightening the nut is the right way to address the issue. Those upper strut mounts can also contribute to turning noises if they are damaged.
