Undercar: Diagnosing And Repairing Wheel Bearing Noise
Adapted from Andrew Markel’s Articles in Brake & Front End
Road testing a vehicle prior to an alignment can be just as important as the alignment itself. Not performing a test drive can lead to comebacks and unhappy customers.
When going for a test drive, a technician should have a clear objective and methodical plan for verifying the problem. It is also a chance to inspect the vehicle for other unperformed repairs.
Before going on a test drive, a technician should have a clear list of symptoms and related conditions the customer is experiencing. Also, before hitting the road the technician should make sure the vehicle is road worthy.
Before You Go…
Verify that car has functioning brakes, lights and enough fuel. Remember, you are driving an unfamiliar vehicle and it may exhibit behavior that could be unexpected, like a seat reclining suddenly. And nothing can be more embarrassing to a technician than running out of gas while driving a customer’s vehicle.
Reasons for Leaving
The main goal of a test drive should be to verify the customer’s problem, not to go get coffee. Also, a good test driver will be able to observe conditions or problems with the vehicle that have developed so slowly the owner is unaware of them.
One of the keys to becoming a good test driver is to find a driving “loop” or route that has a variety of road conditions. Using a predetermined loop can help to build consistency that will help you to spot small problems.
For alignment road tests, your test loop should consist of sections: a flat and straight section; an area to test braking and acceleration; an area with a dip or bump, and an area that offers both left and right turns.
Flat and Straight
On the flat and straight section of the loop, test directional instability and observe steering wheel position. The road surface should be smooth and flat with very little crown. The objective is to drive on a surface that will not influence the direction of the vehicle.
A crooked steering wheel may indicate a thrust condition that should be aligned or corrected. Check for excessive steering wheel play. The vehicle may drift if the steering system is excessively loose. This condition should be repaired before the alignment.
Stop and Start
Use a parking lot or rarely used section of road for this section of the test. This test is used to detect brake pulls, torque steer and worn or loose suspension or steering components.
Check for a brake pull when stopping the vehicle. The owner may think they have an alignment-related problem when, in fact, the braking system is at fault. This is usually most noticeable during hard braking.
The vehicle may drift to one side or the other due to dragging brakes. A brake caliper that does not fully release may be at fault. This problem is often brought about by heat and may not be evident on the alignment rack during compensation of the sensors.
Check for excessive nose-diving during braking. This is not normal and may be caused by worn springs or shocks. Worn springs will affect vehicle ride height and may affect overall vehicle handling. Check for pulls or drifts when accelerating or decelerating. This may be due to a condition known as “torque steer.” Torque steer is generally associated with FWD vehicles.
Dips and Bumps
Drive the vehicle over the bump or through the dip and observe the steering wheel position. This is an excellent test to detect weak springs, weak shocks and worn or unlevel steering components. If the vehicle changes direction or the steering wheel moves excessively, the steering components may be worn, incorrectly adjusted or unlevel. This condition is commonly known as “bump steer.” Excessive suspension bouncing may be the result of weak shocks.
Bottoming out of the suspension may be the result of weak springs. Continue to monitor suspension and steering stability throughout the remainder of the drive.
Left and Right Turns
Check the overall handling response through both left and right turns. Front and rear alignment settings, as well as steering and suspension components, affect cornering capabilities.
Check for steering difficulties that may be the result of mechanical binding or interference. This condition is commonly referred to as “memory steer.” Check for proper returnability of the steering wheel after a turn. Excessive driver effort should not be necessary.
Any excessive body sway could indicate worn springs, shocks or stabilizer assemblies.
Look for any excessive squealing of tires during turns. This can be caused by incorrect alignment settings or turning angle out of specifications.
Developing a methodical and consistent test drive loop and procedure can improve your chances of coming back from a test drive with a better understanding of the problem the owner is experiencing. Having a plan and a loop can eliminate distractions that could lead to an accident. Most importantly, prepare for the unexpected and drive defensively.