Brakes, lines & hoses

Before removing the wheels, pull the parking brake and be sure both rear wheels lock and release easily. You may now remove the wheels in order to inspect the brakes and brake components. This is another simple check which involves the tread depth gauge and a good eye. First use the tread depth gauge to measure the thickness of each inboard and outboard brake pad. This task is much easier if you unbolt the caliper from the hub. You can also get a better look at the pad incase it has cracks or chips in it. On bonded brake pads, under 2/32" fails and on riveted pads, under 1/32" fails. But brake pads should be recommended at 4/32". As for checking the rotor thickness, use your micrometer and compare the rotor thickness measurement to the factory specification. If it is below minimum, the rotor must be replaced. If you felt a brake shimmy on the initial test drive, you might find the reason why. Check and measure the front and rear brakes and compare them to factory specifications. Don't forget to take a close look at the brake hoses and metal lines going to the calipers. If the hoses are cracked enough to see the cord inside it, or the brake lines are leaking, they will need to be replaced before applying a safety sticker.

Tires

Inspecting the tires is the easiest part of the safety inspection. Using a tread depth gauge, check the depth of the tires tread across the full width of the tire. The majority of passenger tires brand new have a tread depth of 10/32nds. A tread depth of under 5/32nds should be replaced for traction reasons but does not fail. If the tread depth of a tire is at 2/32nds on 2 adjacent treads it fails an inspection. Sidewall bubbles from impacts and punctures will cause a vehivle to fail too. Check for edgewear on the tire. This can indicate an alignment problem and you can upsell that to the customer. If there is abnormal wear on a tire and it goes into the secondary layer of rubber this fails. The term for this is secondary wear. This layer of rubber comes right before the metal cords in the tire and is extremely dangerous to drive on. If a customer refuses to install tires with secondary wear, be sure to note down that the customer refused to install tires so in case a blowout does happen, it doesn't fall back on you.

Steering components & wheel bearings

In order to check the rest of the steering components, the vehicle must be lifted into the air with all 4 wheels off the ground. Lift the car to around chest height. Grab each side of the tire and turn it left and right WITHOUT engaging the steering gear. This test checks for play in the tie rod ends. There is an inner and outer tire rod end on every vehicle except some jeeps. To determine which one is loose, have someone shake the wheel until they feel the looseness while you go under the car. To check the outer tie rod, hold it and twist in until it cannot move. To rule out the inner tie rod, hold in and pull it up or down. If the looseness goes away with while holding the outer, then the outer is loose, and vice versa with the inner. To check wheel bearing play, hold the top and bottom of the tire and shake up and down. If any play is felt, have a partner shake the wheel while you go under the car. Feel the axle for movement. If the axle moves the same as the wheel bearing, the wheel bearing is loose. You can also test the wheel bearing by pushing the axle straight up or down which would hold the bearing in place if it is loose. Repeat the above with the rear suspension. Loose tie rods or wheel bearings fail an inspection. Below is a video showing a loose wheel bearing and how to check it.

Checking ball joints

After you are finished with the emissions test it is time to check the suspension components for looseness. Quick tip: If you are working an an SUV or a pickup truck, you should check the ball joints because these parts tend to get loose more often than most vehicles. This can be performed by jacking up each side of the vehicle on the lower control arm. Try to place the jack as close as possible to the wheel, this will take the load off of the ball joint so it can move freely when you test it. After the wheel is off the ground (about 4-5 inches), place your hand on top of the tire and use a pry bar under the tire to life the tire upwards. If either lower or upper ball joint is loose, you will feel it with your hand on the tire. Now to check the upper ball joint, leave the jack where it is, and push and pull the top of the tire. If the upper ball joint is loose, the tire will move in and out. On some volkswagens the lower ball joint can be checked with the car fully lifted in the air. Just place a prybar between the control arm and the steering knuckly and pry up and down gently. Record and play. These suspension problems will fail a safety inspection. Below is a video of a very loose lower ball joint on Toyota 4runner.