DRESSTA TD-25M EXTRA, Service Manual

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SECTION 7
DRIVE TRAIN
Page 12
TD-25M EXTRA DRESSTA
HYDRAULIC OIL FLOW
Power to the left track is transmitted from the pinion shaft to the bevel gear, thru the inner
planetary, to the output shaft and out to the sprocket drive. Power to the right track is transmitted
from the pinion shaft to the bevel gear and from high range clutch directly to the output shaft and
sprocket drive. A right gradual turn is the opposite.
To make a left pivot turn, shift the drive train control lever in the full left position during machine is
moving forward or rearward. The left track is stationary. Power to the right track is transmitted from
the pinion shaft to the bevel gear, thru or without inner planetary to the output shaft and out to the
sprocket drive. A right pivot turn is the opposite.
The two speed steering drive consists of two drive circuits for each side of the machine. The
following describes the operation of both sides.
STARTING AND LOW RANGE STRAIGHT TRAVEL (Fig. 7.4).
When the dozer is started with both speed range switches in LO-LO positions, both tracks are in
low speed range. Main pressure M from the transmission pressure regulator valve enters the upper
valve clutches section LC and RC inlet ports, around the metering spools and on to the HI-LO
sections. Here the oil is divided in two circuits, one to the foot brake FB and one to the HI-LO
spools. At the foot brake FB released, the oil enters the inlet port around the foot brake spool and
out to disengage the brake clutch packs LB and RB. The lower valve contains two HI – LO spools,
one for each side of the machine. These spools are controlled by the high-low solenoids SOL. At
the HI-LO spools in the LO position, the oil is directed by steering manifold J shifted to the right to
engage the LO drive clutch packs.
GRADUAL TURN LEFT (Fig. 7.5).
When the drive train control lever is in drive position with the left speed range switch in its lower
(LO) position and the right speed range switch in its upper (HI) position, the left side steering drive
is working as described above, but on the right side high-low range solenoid SOL is energized. The
solenoid direct pilot oil pressure to right side of HI-LO spool causing the HI-LO spool to shift to HI
range. Oil pressure from the RC clutch section enters the spool bores and is directed out the HI
range port. In this way the right LO clutch pack is released and the right HI clutch pack is engaged.
The machine gradually turns left.
When both speed range switches are in HI-HI positions, both left and right high-low range
solenoids SOL are energized. Both solenoids direct pilot oil to both HI-LO spools causing the HI-
LO spools to shift to HI range. Oil pressure from the both clutch sections enters the spool bores
and is directed out to the high range clutches.
PIVOT TURN RIGHT (Fig. 7.6)
When the drive train control lever is in drive position and it is slowly moved to the pivot position the
metering spool in rear side of this clutch section of the valve begins to meter the main pressure to
the drain annulus, thereby reducing the pressure at the RC clutch annulus which is connected to
both the LO drive and RB brake clutch packs. As the pressure is reduced, the drive clutch pack
releases first and next the brake clutch pack begins to engage. When the drive train control lever is
moved completely to the right pivot position, the pilot pressure CR is dropping down and activates
the metering spool, moving it forward and stops the main oil flow. Then all the pressure is
completely dissipated to the drain annulus, from the right side of the drive and brake clutches.
Machine is in a right brake condition. The machine pivots turn right.
For a more complete description and operation of the steering valve and the steering drive, refer to
SECTION 7E.