Shift Valves

Shift valves are used to direct application pressure to the various shift elements. Shift valves are regulated by spring pressure and control pressure for the shift solenoids. Shift valves come in various configurations depending upon application and transmission type. The most basic is the 3/2 shift valve. The 3/2 shift valve has 2 positions which are switched through one or two control pressures.

With no control pressure from shift solenoid present, the shift valve is moved to its end travel (left) by spring pressure.

Operating pressure is blocked to the shift component. Also in this position any application pressure is drained from the shift component.

Fig 1: Identifying Blocked Operating Pressure To Shift Component

Courtesy of BMW OF NORTH AMERICA, INC.

Once the control pressure is applied to the 3/2 shift valve, the shift valve moves to the right.

This allows operating pressure to reach the shift component.

When the control pressure is again reduced, spring pressure returns the 3/2 shift valve to the rest position. This drains and operating pressure from the shift component.

Fig 2: Identifying Operating Pressure To Reach Shift Component

Courtesy of BMW OF NORTH AMERICA, INC.

The example shown at right is a 4/2 shift valve. The operation is similar to the 3/2 valve. The primary difference is that the 4/2 shift valve affects 2 shift components.

Fig 3: Identifying Primary Difference 4/2 Shift Valve Affects 2 Shift Components

Courtesy of BMW OF NORTH AMERICA, INC.