SECTION 7 DRIVE TRAIN
Page 4
TD-25M EXTRA DRESSTA
OPERATION
The FB foot break section, contains one spool which is held in the drive position by a return spring.
When in this position, oil pressure from the LC and RC sections enters the foot brake section FB
and is evenly split into two separate circuits, one for the LB brake clutch pack and one for the RB
brake clutch pack of steering drive SD. When the foot brake is applied, the spool in this section
moves forward and begins to dissipate the oil pressure to both brake clutch packs simultaneously.
The lower valve consist of two sections LH and RH. Each of section contains HI-LO spool, which
is controlled by solenoid valve SOL and a sequence valve SEQ. These two pairs of valves SOL
and SEQ are placed in one housing of HI-LO valve. This HI-LO valve housing is bolted to the back
of the lower steering valve housing.
Each of sections performs two functions: shifts the HI-LO range spool to HI position when the
solenoid valve SOL is actuated making a high range track speed, and shifts HI-LO range spool
from high to low when solenoid valve is off making a low range track speed.
In case one HI-LO range spool is shifted a gradual turn is making. The left and right steering pilot
pressures enter the HI-LO valve and remains unique to their individual left or right side. The
steering pilot pressure first enters the sequence valve SEQ. When the steering pilot pressure is
above 1370 [kPa], the pilot pressure connects to the solenoid valve SOL. With pilot pressure to the
solenoid SOL, it may send pilot pressure to the HI-LO spool when the solenoid SOL is energized
and it causes, the HI-LO spool shifts to the high position.
The purpose of the sequence valve SEQ is to automatically downshift the HI-LO spool from High to
Low when the main oil pressure decays from the full pressure of 1860 [kPa] to below 1370 [kPa].
When the sequence valve SEQ shifts, it disconnects the pilot pressure to the solenoid valve so that
causes the HI-LO spool moves to the (LO) position.
When the right speed range switch of the drive train control lever is in its upper position (HI) and
the left rocker switch in its lower (LO) position (Fig. 7.5) the drive train electronic controller (EC)
chooses the correct solenoid selections to result in the gradual left turn. The EC controller upshifts
or downshifts the appropriate track to complete the turn.
When the control lever is moved to the right pivot position (Fig. 7.6), the CR pilot pressure drive
train control valve decreases. This dropping pilot pressure activates the metering spool, moving it
forward. The oil pressure to RC and RB clutch is cut off. These right clutches are now connected to
the drain and dozer is pivoting turn right.
When the both rocker switches are in its upper positions (HI) both solenoids SOL are energized.
Both solenoids direct pilot oil to both HI-LO spools causing the HI - LO spools to shift to HI position.
Main oil pressure from the metering spools by HI LO spools sections is directed to both the
HI range clutches ports.
The manifold J covers one spool and spring. The purpose of this manifold is to automatically shift
off the low range clutches when the main oil pressure decays from the full pressure of 1860 [kPa]
to below 860 [kPa].
Switching Valve (10, Fig.’s 7.2 and 7.3)
The switching valve provides a pressure connection for the main low pressure and clutch low oil
pressure warning light switch, allowing enters either “M” - main pressure to the switch, when the
drive train control lever is in the neutral position, or “PC” – gear clutch pressure when the drive
train control lever is in the forward or reverse position.
Gear Shifting Valve (11, Fig.’s 7.2 and 7.3)
Gear shifting valve is an electronically controlled transmission range gears valve. The valve
housing contains two solenoids: one for the second gear (11A) and the other one – for the third
gear (11B). When the machine is started both solenoids are de-energized and drive begins in the
default condition of transmission that is in the first gear position. When the up-shift control button is
pressed once the second gear solenoid is energized and the second gear is selected. With
pressed up-shift button once again the third gear is selected (the third gear solenoid is energized).
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