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What Your Mechanic Doesn't Want You to Know

By Austin C. Davis
Posted Monday, January 3, 2005

Reader Question: My car shakes and vibrates on the freeway, does this mean I need a front end alignment?

Dear concerned car owner,

How do you know if your car needs a front end alignment? Vibrations, shimmy, and shaking felt in the steering wheel are usually not a sign of needing a front end alignment. A front end alignment, or four wheel alignment as it is commonly referred to these days due to the fact that the rear end of the vehicle can also be adjusted, does just what the name implies align, or line up the direction of the wheels so the vehicle is pointed in a straight line.

Caster, camber, and toe are terms used to describe the direction of the wheel in relation to the body of the vehicle. The front of the tire can be pointed in toward the center of the vehicle thus "toed in." When the front of the tire is pointed outward, it is referred to as "toed out." Both of these problems can quickly wear down the tread of a tire and can cause a "pull" in one direction of the front end. The top of the wheel can also lean in toward the center of the vehicle or lean out away from the vehicle, causing a camber problem. This situation can also cause tire wear and a pull to one direction in the front end. Caster measures the relationship of the left and right wheels to each other. If one wheel is farther forward or back from the other wheel, then there is a caster problem. Caster will usually not cause a pull or tire wear, and this problem is commonly found on wrecked vehicles.

So what causes shimmy and shakes in the front end? The biggest culprit is an out-of-balance or out-of-round tire. As the tread on the tire wears, it will need to be re-balanced to evenly distribute the weight of the tire and the wheel. To do this, small lead weight is attached to the outside of the wheel and a machine is used to spin the tire and wheel to check balance. Tires should be balanced and rotated every 12,000 miles (approximately every four oil changes) to ensure even tire wear and extend tread life. Out-of-round means the tire has worn unevenly and cannot be balanced. An out-of-round tire will have to be replaced. I have even seen new tires that were out-of-round due to a manufacturing defect.

Hitting a curb or large pot hole can cause the wheel weights to come off, and sometimes the weights sling off the wheel at high speed if they were not installed properly. Out-of-round or out-of-balance will not cause a pull in the front end, but will definitely cause shakes and shimmies. If you can drive out of a shake or shimmy by varying the speed of the car, it is a good clue that you have an out-of-balance problem. A simple way to check tire balance: if the shimmy is present at one speed, but better or not present at a different speed, then a balance problem is likely. An out-of-round tire or a bent wheel will usually produce a wobble or shimmy at all speeds, and replacement of the tire or wheel is usually the cure.

Regular tire rotation is the best way to extend the life of a tire. Ask your mechanic which way to rotate the tires depending on how the tread is wearing. Crossing tires in an "X" pattern is usually the standard way to rotate most tires, but moving the front tires to the back in some cases is recommended to place the best tires on the front. The majority of the stopping power of the vehicle comes from the front brakes, so the best tires should stay on the front for safety. Caution: Some tires are "directional" and must stay on one side of the vehicle, due to the fact that the tire was made for the tread to only travel in one direction.

A vibration or shaking that is felt in the steering wheel only when the brakes are applied is not a front end alignment problem, but a brake problem. Have the brakes inspected and make sure to tell your mechanic about the shaking that you feel in the steering wheel when you apply the brakes. This vibration may not be felt by the mechanic on a quick test drive around the block, so be specific. During this brake inspection, it would also be a great time to rotate the tires since you are already paying the labor to remove the wheels.

I have developed a quick and easy to use maintenance schedule that can help keep you up-to-date on the items mentioned above. These schedules are free for you to view and print out


About the Author
Austin Davis comes from a family that has been in the auto repair industry for over 64 years. Austin speaks at local civic events, at area clubs and organizations and has written a book “What Your Mechanic Doesn’t Want You To Know”. His book is about how to find an honest mechanic, and the simple steps to keep them honest. Austin points out that it is usually what the customer says or does that can cause them to be taken advantage of by a repair “professional.”


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