the steering brake hub. This hub then rotates with the
planetary carrier, and no power is transmitted to the
sprocket drive shaft.
Occasionally, an adjustment of the steering brake
is required to prevent slippage when it is engaged.
Consult the manufacturer's service manual for
The pivot brakes on tracked equipment are of the
multiple disc type. Pulling the steering brake levers
fully to the rear operates them. The middle discs
(splined to the sprocket drive shaft) have laminated
linings. The intermediate discs (held in position by
studs) are smooth steel discs. An actuating disc
assembly is two steel plates with steel balls between
them. The assembly is located in the center of the discs
and is connected to the operating linkage.
Ramps are machined on the steel plate of the
actuating disc assembly, so when the brakes are
applied, the steel balls move up the ramps and force the
plates apart. Movement of the plates causes the discs to
be squeezed together and to stop rotation of the
sprocket drive shaft. When these brakes are fully
applied, the tracks will stop. The steering levers are
linked to the brakes independently to actuate them for
Adjustment of the pivot brakes is required to
provide adequate braking with the steering levers. An
adjustment is required when the steering levers can be
pulled against the seat with the engine running.
Consult the manufacturer's service manual for proper
HYDROSTATIC DRIVE TRAIN
The hydrostatic drive is an automatic fluid drive
that uses fluid under pressure to transmit engine power
to the drive wheels or tracks.
Mechanical power from the engine is converted to
hydraulic power by a pump-motor team. This power is
then converted back to mechanical power for the drive
wheels or tracks.
The pump-motor team is the heart of the
hydrostatic drive system. Basically, the pump and
motor are joined in a closed hydraulic loop; the return
line from the motor is joined directly to the intake of
the pump, rather than to the reservoir (fig. 6-11). A
charge pump maintains system pressure, using supply
oil from the reservoir.
The hydrostatic drive functions as both a clutch
and transmission. The final gear train then can be
simplified with the hydrostatic unit supplying infinite
speed and torque ranges as well as reverses speeds.
To understand hydrostatic drive, you must
understand two principles of hydraulics:
Liquids have no shape of their own.
Liquids are not compressible.
The basic hydrostatic principle is as follows (fig.
Two cylinders connected by a line both filled
with oil. Each cylinder contains a piston.
When a force is applied to one of the pistons, the
piston moves against the oil. Since the oil will
not compress, it acts as a solid connection and
moves the other piston.
In a hydrostatic drive, several pistons are used to
transmit powerone group in the PUMP sending
power to another group. in the MOTOR. The pistons are
in a cylinder block and revolve around a shaft. The
pistons also move in and out of the block parallel to the
Figure 6-11.Pump and motor form a closed hydraulic loop.
Figure 6-12.Basic hydrostatic principle.