Service Manual

2 HGM-H
movement out of the cylinder block, it gets
pushed back into the cylinder and uid inside
the piston is discharged through the low pres-
sure port of the motor. Pistons develop torque
only through half of the cylinder block rotation
cycle. Therefore, multiple pistons are used to
provide a constant and continuous torque to
the motor shaft. Reversing the direction of the
incoming pressurized uid into the motor re-
verses the direction of the motor output rotation.
A hydraulic bypass is utilized in a hydraulic
system to permit moving the vehicle for a short
distance at a maximum of 2 m.p.h. (3.2 Km/h)
without starting the engine. The bypass will be
located on the hydraulic pump.
The HGM-H series motor utilizes a friction
type brake controlled by a cam attached to an
external actuating arm.
INTRODUCTION
The purpose of this manual is to provide in-
formation useful in servicing the Hydro-Gear
®
HGM-H series motor. This manual includes
the HGM-H series motor general description,
hydraulic schematic, technical specications,
servicing and troubleshooting procedures.
Should servicing be required, the exterior of the
motor will need to be thoroughly cleaned before
beginning most procedures. Do not wash the
transaxle while it is hot. Do not use a pressure
washer to clean the unit.
GENERAL DESCRIPTION
The HGM-H series hydraulic motors are xed
displacement axial piston motors. The motor
is designed to convert hydraulic power into ro-
tational power at the axle shaft. It operates at
an innitely variable speed range between zero
and maximum axle speed determined by motor
displacement and maximum pump ow in both
forward and reverse modes of operation.
The HGM-H series motor is available with a
xed displacement of 15 cu. in. or 18 cu. in. (245
to 294 cc) maximum per revolution. The cylinder
block pistons in the HGM H series motors are
set at a xed displacement by a swash angle
that is integral to the motor housing. Therefore,
the motor is always at maximum displacement.
As pressurized uid from the pump pushes
against the cylinder block pistons, they forced
to rotate with the thrust bearing. As the pistons
rotate with the thrust bearing, they create torque
and rotory motion that is transmitted to the axle
shaft. Torque continues to develop as long as
the piston is being pushed out of the cylinder
block. When the piston reaches the end of the
DESCRIPTION AND OPERATION