SUBSECTION 6 HYDROSTATIC PUMP AND MOTOR
RECOMMENDED REPAIR OF PUMPS AND MOTORS IN THE FIELD
Certain repairs can be made by mechanics who use care not to damage new parts and use precaution to keep
contamination out of the system. For instance, the seals on the driving end of both pumps and motors are replaceable
without much trouble.
On the pump the charge pump, gasket, relief valve check valves and displacement control valve are easily replaced.
On the motor, the entire relief valve manifold can be changed. The high pressure relief valves, low pressure relief valve
and shuttle valve are easily replaceable.
The above repairs can be made without affecting the pump or motor warranty.
A COMPLETE OVERHAUL OF BOTH PUMPS AND MOTORS CAN BE MADE ONLY BY FACTORY APPROVED
AND TRAINED SERVICEMEN. CUSTOMERS ARE CAUTIONED AGAINST ATTEMPTING AN OVERHAUL OF A
HYDRAULIC PUMP OR MOTOR AS THIS WILL VOID THEIR WARRANTY. THE FOLLOWING PARAGRAPHS ARE
PROVIDED FOR BACKGROUND INFORMATION ONLY AND SHOULD NOT BE CONSTRUED TO MEAN THAT
REXWORKS RECOMMENDS FIELD OVERHAUL OF EQUIPMENT BY CUSTOMERS. EXCEPT FOR THE MINOR
REPAIRS SPECIFIED ABOVE, WE STRONGLY RECOMMEND THE COMPLETE REPLACEMENT OF DEFECTIVE
PUMPS AND MOTORS.
The hydrostatic mixer drive consists of a diesel powered engine, a variable displacement over-center piston type pump, a
fixed displacement piston type motor, a reduction gear case, suitable hydraulic lines, and other components such as oil
reservoir, filter, charge pump, relief valves, and control system.
The variable displacement pump is driven by the engine by means of a universal joint driveline. The remote control
lever for travel speed is mounted on the control panel and is connected to the pump control lever by means of push-pull
The variable displacement pump has a neutral position in which no fluid is pumped to the motor. Moving the control
lever forward or rearward of neutral, while the engine is running causes oil to be pumped to the motor; one side turning
the motor in a forward direction, the other side in a reverse direction. The further the control lever is moved from the
neutral position, the faster the machine runs. Changing the engine speed will also change the travel speed providing the
pump control lever is not in neutral position. If it is in the neutral position, the machine will not travel.
The hydrostatic motor is coupled directly to the reduction gear case of the rear axle differential. Hydraulic lines connect
the pump and motor and other components in the hydrostatic circuit.
CAUTION AND IMPORTANT:
The most serious thing to have happen to the hydrostatic system is for dirt or foreign material to be introduced into the oil
in any way. Introducing solids of any kind or liquids other than clean hydraulic oil will cause almost immediate failure. If
for any reason, any component is removed for repair, the connections must be first cleaned with a solvent and dried
before disassembly. Plug or protect openings to keep foreign matter from entering the hydraulic system. Do not use
cloth or paper as a material for protection.
When adding or changing oil, pour oil thru a clean #200 mesh screen funnel. Do not use cloth as a filter. If necessary to
seal pipe threads, use Permatex Sealer Grade #2 on male threads only. Keep the sealer back from the end of the male
threads by at least 1/8.