Measuring Wheel Drag
Wheel Drag: The Problem
Accurately determining wheel drag during diagnosis
The Cause of Misdiagnosed Wheel Drag:
Many mechanics judge the amount of drag by rotating the tire/wheel assembly by hand, which is not always an accurate method of determining drag.
How to Measure Drag:
When diagnosing the cause of a drag check, it is essential to accurately determine if the results of a test step impacted the amount of drag. Some drag conditions result in only a slight drag, making diagnosis more difficult.
The most accurate method to determine the drag on a wheel is to use an inch-pound torque wrench. This method is also the best method to use when trying to determine the amount of change on drag during a diagnostic test. To perform a drag test using an inch-pound torque wrench, follow the steps below:
1. Duplicate the drag condition
2. Adjust the torque wrench to a midway setting such as 30 (Figure 53.1)
3. Position a wheel stud to the three o’clock position as shown in Figure 53.2
4. Place the torque wrench on the lug nut at the three o’clock position.
5. Attempt to rotate the tire/wheel assembly while noting whether or not the torque wrench clicks. If the torque wrench clicks before the wheel turn, go to the next step. If the torque wrench does not click before the wheel rotates, go to step 7.
6. Torque wrench clicks before wheel rotates – adjust the torque wrench to a higher setting and attempt to turn the wheel. A good rule of thumb is to increase it by 10. Repeat this step until the wheel rotates when the torque wrench clicks.
7. Wheel rotates before torque wrench clicks – adjust the torque wrench down and rotate the wheel. A good rule of thumb is to decrease it by 10. Repeat this step until the wheel turns when the torque wrench clicks.
TIP: When diagnosing a one-wheel drag condition, measure the drag on the opposite (non-dragging) wheel to use as a comparison. When performing diagnostic steps to determine the cause of a drag, use the opposite wheel’s drag measurement to determine if the dragging wheel is completely releasing. See page 94 for one-wheel drag diagnosis
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