DRESSTA TD-25M EXTRA, Service Manual

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SECTION 7
DRIVE TRAIN
Page 2
TD-25M EXTRA DRESSTA
GENERAL
Power from the engine is transmitted through a flywheel drive ring to the torque converter (2). Drive
shaft (3) couples the output flange of the torque converter with input yoke (4) of transmission (5).
The converter delivers torque according to the variation in load on the oil used as the medium, and
transmits the power to the transmission (5). When the transmission is engaged, power is
transmitted from the output shaft of the transmission to the pinion shaft of steering drive (8), and by
steering drive clutches to the steering drive output shaft (10), then through final drives (13) and
sprockets (14 and 15) to the tracks.
3. DRIVE TRAIN MAIN COMPONENTS
The torque converter (2, Fig. 7.1) contains a single stage, single phase, three element converter
assembly and a drive gear to drive the drive train charge and scavenge pump, the equipment
pump and the fan drive pump. The torque converter main function is to multiply engine torque.
The transmission (5) is designed to provide high speed shifting by use of hydraulically actuated
clutch packs. It has three forward and three reverse speeds. Gears are mounted on four shafts:
directional (input) shaft, range (output) shaft, countershaft and reverse idler shaft.
The steering drive (8) is a unit constructed into a housing similar to a transmission. This design
affords ease of assembly and service. The machine is equipped with the two speed steering drive.
The two speed steering drive contains one low range clutch pack, one high range clutch pack, one
brake clutch pack and a planetary on each side of the machine. The low and high range clutch
packs are hydraulically applied and spring released whereas the brake clutch packs are spring
applied and hydraulically released. An inner planetary provides the reduction in speed for the low
range. If a hydraulic failure occurs or the engine is stopped, the steering drive will automatically
apply the brakes.
The final drive (13) consist of a set of spur gears and a planetary on each side at the rear of the
machine. Power is transmitted from the steering drive to each of the final drives. Double reduction
in the final drive is accomplished by a pinion to bullgear arrangement for the first reduction and
a planetary set for the final reduction.
OPERATION
4. DRIVE TRAIN SYSTEM VALVES
Drive Train Control Valve (12, Fig.’s 7.2 and 7.3)
The drive train control valve is a manually controlled direction, range and steering control valve.
The valve is used to direct main oil pressure to the transmission range selector valve for
transmission control and to the steering control valve for range and steering control. A detent
mechanism holds the control lever in the desired transmission direction.
Main pressure from the charge pump through hydraulic damper, pressure filter and drive train
neutral lock solenoid valve enters the drive train control valve at the “M” port and is distributed to
the direction and steering spools. When the control lever is in the centered “neutral” position, oil is
active at the selected steering ports but is blocked at the direction spools.