A technician is measuring the torque required to rotate the pinion on a drive axle using a spring scale. Technician A says to start with the parts stationary, and read the scale while gradually increasing the tension on it. Technician B says to rotate the pinion and pull it at a slow steady speed while reading the scale. Who is right?

• A. Start with the parts stationary, and read the scale while gradually increasing the tension on it.
• B. Rotate the pinion and pull at a slow steady speed while reading the scale.
• C. Both A and B.
• D. Neither A nor B.

Answer: (B)

The key idea is to measure torque under steady, running conditions, not at the moment you just start moving. When you apply a spring scale and turn the pinion, the force you read should reflect the resistance to turning once the parts are in motion, including gear friction and any load on the axle. If you start from rest and gradually increase tension, you’re capturing the static or start-up torque, which is typically higher and not representative of the ongoing resistance you’d see during normal operation. It can also be harder to get a stable, repeatable reading as you fight static friction and potential binding.

Rotating the pinion and pulling at a slow, steady speed while reading the scale gives a consistent, running torque reading at that speed. The scale’s force, combined with the known lever arm, corresponds to the torque the system resists during operation, making the measurement meaningful and repeatable. So Technician B’s method is the proper approach.