Transmission Hydraulic Control
The transmission hydraulic controls are attached to the top of the planetary transmission on the inside of the
Proportional solenoid valves are mounted on the relief valve manifold. The machine has one modulating valve for
Each modulating valve has a pilot stage that is similar to the type of proportional solenoid valve that is used for the
brakes. Each modulating valve also contains a pressure reducing spool. Modulating valve allows the
corresponding clutch to fill to a pressure that is proportional to the current to solenoid.
The ECM determines the amount of current that is required by the solenoids. The current is based on the response
of the machine, which is measured by speed sensors.
Modulating valves are designed to be individually replaced if a malfunction occurs.
Transmission clutch pressures can be measured from the pressure taps that are remotely located on the back of
the transmission case.
N OT E
Transmission modulating valves must be recalibrated when any of the following tasks are
A transmission modulating valve and/or a solenoid is replaced.
The transmission is serviced or the transmission is replaced.
The ECM is replaced.
Main Relief Valve
The main relief valve is located in the relief valve manifold on the top of the planetary transmission and maintains
the system pressure in the high pressure circuit (control section) of the powertrain oil pump.