On Allison transmissions, the ______ valves direct clutch apply pressure to the clutch packs.

On Allison transmissions, the ______ valves direct clutch apply pressure to the clutch packs.

• A. shift relay
• B. modulator
• C. shift signal
• D. trimmer

Answer: (A)

In an Allison transmission, hydraulic pressure to apply the clutches is directed by shift relay valves. These valves route the pump pressure to the correct clutch packs when a gear change is commanded, allowing the right clutches to engage smoothly for the selected gear. The modulator valve is used in some older systems to regulate pressure based on engine conditions, not to direct clutch apply pressure. The shift signal is a control input, not a valve, and a trimmer isn’t a part of this clutch-control path. So the shift relay valves are the ones that directly manage clutch apply pressure.

In an Allison transmission, hydraulic pressure to apply the clutches is directed by shift relay valves. These valves route the pump pressure to the correct clutch packs when a gear change is commanded, allowing the right clutches to engage smoothly for the selected gear. The modulator valve is used in some older systems to regulate pressure based on engine conditions, not to direct clutch apply pressure. The shift signal is a control input, not a valve, and a trimmer isn’t a part of this clutch-control path. So the shift relay valves are the ones that directly manage clutch apply pressure.