A truck with a single countershaft, synchronized transmission shows a rough, uneven sound in one of the lower gears. A gear tooth is broken. Who is right about the cause?

A truck with a single countershaft, synchronized transmission shows a rough, uneven sound in one of the lower gears. A gear tooth is broken. Who is right about the cause?

• A. Technician A only
• B. Technician B only
• C. Both A and B
• D. Neither A or B

Answer: (B)

The rough, uneven sound in the lower gears along with a broken gear tooth points directly to a mechanical damage inside the gear train. When a tooth is broken, the gear can’t mesh smoothly with its mate, causing intermittent contact, vibration, and noise under load—something you’d expect most in the lower gears that take the most torque in a single-countershaft, synchronized setup. Other causes like worn synchronizers or loose bearings would produce different symptoms (such as grinding during shifting or bearing rumble) rather than a tooth that’s visibly broken. So the best explanation is that the broken tooth is the root cause of the symptom.

The rough, uneven sound in the lower gears along with a broken gear tooth points directly to a mechanical damage inside the gear train. When a tooth is broken, the gear can’t mesh smoothly with its mate, causing intermittent contact, vibration, and noise under load—something you’d expect most in the lower gears that take the most torque in a single-countershaft, synchronized setup. Other causes like worn synchronizers or loose bearings would produce different symptoms (such as grinding during shifting or bearing rumble) rather than a tooth that’s visibly broken. So the best explanation is that the broken tooth is the root cause of the symptom.