In the Allison AT series, if the trimmer valve is stuck open, what is the likely outcome for the clutch controlled by that trimmer?

In the Allison AT series, if the trimmer valve is stuck open, what is the likely outcome for the clutch controlled by that trimmer?

• A. The clutch would not engage
• B. The clutch would engage too early
• C. The clutch would have a harsh engagement
• D. The clutch would slip and burn out

Answer: (D)

The essential idea is that the trimmer valve sets how much hydraulic pressure reaches the clutch in the Allison AT series. If that valve sticks open, pressure to the clutch is bled away, so the clutch doesn’t receive enough force to fully grab. With inadequate pressure, the clutch can’t apply smoothly and will slip when torque is applied. This continuous slipping generates heat in the clutch pack, and over time the friction surfaces can overheat and burn. So the most likely outcome is that the clutch would slip and burn out. The other possibilities don’t fit this failure mode as well: reduced pressure tends to cause slipping rather than a guaranteed early or harsh engagement, and a complete loss of engagement would require a more severe or different failure scenario.

The essential idea is that the trimmer valve sets how much hydraulic pressure reaches the clutch in the Allison AT series. If that valve sticks open, pressure to the clutch is bled away, so the clutch doesn’t receive enough force to fully grab. With inadequate pressure, the clutch can’t apply smoothly and will slip when torque is applied. This continuous slipping generates heat in the clutch pack, and over time the friction surfaces can overheat and burn. So the most likely outcome is that the clutch would slip and burn out.

The other possibilities don’t fit this failure mode as well: reduced pressure tends to cause slipping rather than a guaranteed early or harsh engagement, and a complete loss of engagement would require a more severe or different failure scenario.