Allison transmissions use the __________ valves to slow down the shift slightly to make the engagement more gradual.

• A. Trimmer
• B. Hold regulator
• C. Shift modulator
• D. Priority

Answer: (A)

Smooth shifts in an Allison automatic come from controlling how quickly hydraulic pressure builds in the clutch apply circuits. The trimmer valve acts as a fine-tuning element in the valve body, introducing a small delay in the shift signal. That delay slows the pressure rise to the clutches just enough to make the engagement gradual, reducing shock and wear as gears mesh. Other valves have different jobs: the hold regulator keeps minimum hold pressure to prevent slip, the shift modulator adjusts shift timing in a broader sense, and the priority valve ensures essential oil pressure is available for other circuits. So the trimmer valve is the one specifically designed to slow the shift slightly for a smoother engagement.