DRIVE TRAIN SECTION 7
Page 5
DRESSTA TD-25M EXTRA
OPERATION
Drive Train Neutral Lock Solenoid Valve (17, Fig.’s 7.2 and 7.3)
The drive train neutral lock solenoid valve blocks flow to the drive train control valve when the drive
train neutral lock lever is in the lock position, and allows flow to drive train control valve when the
drive train neutral lock lever is in the unlock position. The drive train neutral lock solenoid valve
contains normally closed solenoid valve. When starting the machine the neutral lock lever is in the
lock position and the solenoid valve is deenergized. The oil under main pressure enters the neutral
lock solenoid valve. The normally closed solenoid valve blocks the flow. In this condition the drive
train control valve and transmission is not operational. When the neutral lock lever is moved to the
unlocked position, an electric switch is closed sending power to the solenoid valve. The energized
solenoid valve opens and directs flow to the drive train control valve. The drive train control valve
and transmission is now operational.
Priority Valve (18, Fig.’s 7.2 and 7.3)
The purpose of the priority valve is to maintain a steady pressure to the transmission and steering
valve. Transmission pump flow enters the priority valve. The regulated pressure branches off and
is connected to the drive train neutral lock solenoid valve. When the priority pressure of 1890 [kPa]
setting is met, the valve opens and flow continues on to the pressure regulator valve mounted on
the transmission.
The Pressure Regulator Valve, the Rate of Rise Valve and the Range Selector Valve are
described in a separate section. For a complete description and operation, refer to SECTION 7C.
HYDRAULIC OIL FLOW
5. TRANSMISSION SYSTEM OIL FLOW (Refer to Fig.’s 7.2 and 7.3)
The rear part of main frame (9) is the common oil reservoir for torque converter, transmission and
steering drive. When the engine is running, oil is drawn out from the bottom of the main frame (9),
through suction strainer (2) and onto the rear charge element (3) of drive train charge and
scavenge pump.
The charge element (3) of drive train charge and scavenge pump delivers oil flow through hydraulic
damper (22), pressure oil filters (5) and priority valve (18) to the M port of pressure regulator valve
(15) and to steering control valve by line (19). This charge pump element delivers also oil flow
through unlocked drive train neutral lock solenoid valve (17) to drive train control valve (12). Oil
from the pressure regulator valve (15) M port is directed through two internal passages in
transmission manifold to rate of rise valve (14) and through one passage to P port of range
selector valve (13). Oil from the pressure regulator valve (15) M port is also directed by hoses to
gear shifting valve (11) and switching valve (10),
The main pressurized oil directed to drive train control valve (12) enters the M port and can be
directed out to either the F or R port. When this oil is directed out of one of these ports, it is routed
by hose to range selector valve (13) to shift the valve directional spool and switch spool. These
spools are visible in lower part of valve (13).
When this shift occurs, the main pressurized oil is directed to rate of rise valve (14) by P, P1 ports
of range selector valve (13) and is passed onto the FR and PC ports of range selector valve (13).
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