Repair manual

RD 27 Troubleshooting the Drive System
wc_tx000949gb.fm 51
4 Troubleshooting the Drive System
Best practice The best practice when troubleshooting this system is to:
1. Isolate and check each component of this system individually.
2. When a malfunctioning component is found, repair or replace it.
3. After replacing a malfunctioning component, retry system operation.
This chapter provides procedures to check the components.
4.1 Drive System Overview
Major
components
The major components of the drive system are:
 Drive pump
 Drive motors
 Steering pump
 FWD/REV control valve
 Seat switch solenoid
 Neutral/brake solenoid
Drive pump  The drive pump is a variable displacement, axial piston pump.
 Charge pressure for the pump is supplied by the steering pump.
 Engine rotation turns the pump drive shaft which then rotates the drive pump’s
piston barrel assembly. The pump’s internal slipper pads allow the pistons to fol-
low the angle of the swash plate. The swash plate angle is determined by the
pump’s servo piston, its position is controlled by the FWD/REV control lever.
The further from the neutral position the FWD/REV control lever is moved, the
greater the angle of the swash plate, which in turn means greater flow from the
pump, thus faster movement of the drive motors.
 The drive pump includes a charge relief valve which provides relief of the
charge system if pressure builds up to 24±1 bar (348±14 psi).
 The drive pump includes makeup relief valve cartridges whose function is to
provide makeup oil supply to the drive system if any has been lost due to leak-
age or slippage of the drive motors.
 The drive pump includes two main relief valves that provide high-pressure relief
if pressure builds up to 350±25 bar (5000±363 psi). Excess oil is directed back
into the pump case and/or back to the tank.
Drive motors  There are two drive motors—one mounted to each drum.
 The drive motors are plumbed in parallel.
 Each drive motor is equipped with Spring Activated Hydraulically Released
(SAHR) brake.
 Each drive motor includes a case drain.
Steering
pump
Charge oil to the drive system is provided by the steering pump. Oil flows from the
steering pump through the charge filter and into the drive pump.