TM 5-3805-291-23-1
THEORY OF OPERATION - CONTINUED
0003 00
POWERTRAIN - CONTINUED
c.
Six hydraulically activated clutches in transmission provide four forward and four reverse speeds. Speed and direc-
tion selections are made manually with transmission direction and speed control. Autoshift control makes speed
selections if machine is in AUTOMATIC mode. Variable shift control uses position of variable shift control switch
and engine speed to provide alternate autoshift points.
d.
Powertrain ECM electronically controls transmission shifts using operator input from transmission direction and
speed control and left brake pedal position sensor. Powertrain ECM signals transmission clutch modulating valves
on selected speed clutch and selected direction clutch. Output signal energizes selected modulating valve sole-
noids. Energized transmission clutch modulating valves electronically modulate oil pressure for selected clutches.
Powertrain ECM can request automatic shifts.
e.
Powertrain ECM uses these input signals to ensure steady clutch engagement: engine speed sensor, torque con-
verter output speed sensor, transmission speed sensors, and transmission oil temperature sensor.
f.
Powertrain ECM main functions include: neutral start, manual shift, automatic shift, transmission neutralizer,
parking brake, backup alarm, secondary steering, ride control, speed limiter (if equipped), and diagnostic opera-
tion.
2.
Neutral Start Function.
a.
Start relay is powertrain ECM output which turns start solenoid ON and OFF. Start solenoid controls starting
motor. When an operator turns engine start switch to START position and conditions are satisfied, powertrain
ECM energizes start relay with a +battery signal. Powertrain ECM will not allow engine to start unless transmis-
sion direction and shift lever is in NEUTRAL. If transmission direction and shift lever is in NEUTRAL, power-
train ECM activates start relay. Start relay allows starting motor to turn. Powertrain ECM will not allow starter to
activate if engine is running. Also, high battery voltage can prevent starter activation.
b.
Start relay has a connector with two contacts. One contact receives power from powertrain ECM connector contact
J1-1 and one contact returns power to powertrain ECM connector contact J2-1.
c.
Start relay Terminal 3 connects to a +battery source. Terminal 4 connects to start solenoid.
3.
Manual Shift Function.
Table 1. Modulating Valve (Transmission Clutch).
Speed and Direction
Clutch(es) Engaged
Fourth Speed Forward
3 and 2
Third Speed Forward
4 and 2
Second Speed Forward
5 and 2
First Speed Forward
6 and 2
Neutral
3
First Speed Reverse
6 and 1
Second Speed Reverse
5 and 1
Third Speed Reverse
4 and 1
Fourth Speed Reverse
3 and 1
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