TM 5-3805-291-23-1
THEORY OF OPERATION - CONTINUED
0003 00
POWERTRAIN - CONTINUED
b.
Modulating Valve (Transmission Clutch).
427-C1737
(1)
Transmission clutch solenoid modulating valves are mounted on top of transmission under cab. There is
one modulating valve for each of six transmission clutches.
(2)
Modulating valves are powertrain ECM outputs. Transmission clutch solenoid modulating valves are pro-
portional solenoid valves used by powertrain ECM to directly modulate oil pressure sent to each individual
clutch. When an operator selects a direction or speed, powertrain ECM sends a PWM to vary current to
clutch solenoid. Distance travelled by solenoid plunger (valve) is proportional to solenoid electrical cur-
rent. Position of solenoid plunger (valve) controls oil pressure of selected clutch. Amount of current sent to
modulating valve regulates amount of oil pressure supplied to selected clutch. When powertrain ECM
sends maximum current to modulating valve, oil pressure in clutch is at maximum. When no current is sent
to modulating valve, oil pressure in clutch is at minimum.
(3)
Powertrain ECM will activate modulating valves selected by operator. Modulating valves (1 and 2) supply
oil to direction clutches. Modulating valves (3, 4, 5, and 6) supply oil to speed clutches. To move machine,
one speed clutch solenoid and one direction clutch solenoid must be energized. When transmission is in
NEUTRAL, only one modulating valve (3) is energized. When transmission is shifted to NEUTRAL,
direction clutch solenoid is de-energized and present speed clutch solenoid is energized.
C AU T I O N
The solenoid coils are not designed to be operated at 24 DCV directly. The powertrain ECM sends a 24V
PWM signal at a duty cycle which provides an average voltage of about 12V to the solenoid coils. DO NOT
ENERGIZE THE SOLENOID COILS WITH 24 DCV (+battery). The life of the solenoid coils will be dras-
tically reduced if they are energized with 24 DCV (+battery). If the solenoid coils must be energized by a
source different from the powertrain ECM, use 12 DCV to energize them.
(4)
Modulating valves have a connector with two contacts. One contact receives power from corresponding
powertrain ECM connector contact (J1-48, J1-49, J1-51, J1-62, J1-65, and J1-66). Other modulating valve
contacts join together. Contacts return power to powertrain ECM connector contacts J1-50, J1-55, and J1-
60.
0003 00-51
