I have a d5c III dozer with the hystat drive system. The…

Hello,

If the tractor is turn to the left, the left side is not driving the machine.

The surging is odd but not uncommon when a pump or motor port plate is damaged.

You likely have damage to the left drive pump and/or the left drive motor.

Both pumps and the left motor should be removed for inspection to find any damage to the port plates and possible the the rotating assemblies in them.

The oil cooler is part of the return circuits. The check ball could have come from any part of the system. It does take flow from the drive motors so, it could be more likely from a drive motor.

I haven't rebuilt any of these and cannot say where that check ball would have come from.

A complete series of pressure testing might show if a pump has become weak but, it is likely the end result would be pulling the pumps and motor anyway.

If I had to make this repair, the pressure testing would be first. However, some machines had special fittings due to the high pressure in the hydrostatic loop and this tooling is different from the standard testing tools.

If the testing only indicates pilot control pressure problems, you may be lucky and only need a joystick control valve. I don't think the joystick is the issue if you have the same control problem forward and reverse. It would not be common for both directions to have the same control problem on one side only.

Below is a complete list of hydrostatic problems and the possible causes CAT says can be related to this machine.

Please review each and let me know if you find something that matches your complaint better.

Performance Tests

The front hydrostatic pump maintains the left track and the rear hydrostatic pump maintains the right track.

Each hydrostatic pump contains a charge pump. The front charge pump provides signal oil. The rear charge pump provides the oil that releases the parking brake and the oil to the overspeed control valve. This pertains to (S/N: 5HS1-566), (S/N: 6CS1-543) and (S/N: 7PS1-854) for the D5C only. Each charge pump has a relief valve.

The oil pressure that opens the relief valves must meet specifications. Pressures that are too low will cause a decrease in a machine's performance. Pressures that are too high will cause a decrease in the life of hoses and components. Pressures that are too high can cause performance problems.

Problem

Both hydrostatic pumps make noise. The tracks do not move smoothly and there are air bubbles in the oil.

Probable Cause

1. The hydraulic oil level is low.

1. There is a leak in the suction line.

1. The viscosity of the hydraulic oil is incorrect.

Problem

One hydrostatic pump makes noise. The track for that pump does not move smoothly. There are air bubbles in the oil.

1. The crossover relief valve opens at low oil pressure.

1. The connection of the oil line on the inlet side of the hydrostatic charge pump is loose.

1. The connection of an oil line between the hydrostatic pump and motor is loose.

1. The hydrostatic pump or the hydrostatic motor has too much wear.

Problem

The output of both hydrostatic pumps is low.

Probable Cause

1. The oil level is low.

1. The viscosity of the hydraulic oil is incorrect.

1. The front hydrostatic pump's charge relief valve is not set to the correct specifications.

1. The front hydrostatic pump's speed sensing valve's adjustment is not set to correct specifications.

1. The cable for the front hydrostatic pump's speed sensing valve is not properly adjusted.

1. Parking brake linkage adjustment is not set to the correct specifications.

1. The linkage for the speed override and brake control is not set to correct specifications.

1. The rear hydrostatic pump's charge relief valve is not set to the correct specifications. This pertains to (S/N: 5HS1-566), (S/N: 6CS1-543) and (S/N: 7PS1-854) for the D5C only.

1. The rear hydrostatic pump's speed sensing valve's adjustment is not set to correct specifications. This pertains to (S/N: 5HS1-566), (S/N: 6CS1-543) and (S/N: 7PS1-854) for the D5C only.

1. The overspeed control valve is not set to correct specifications. This pertains to (S/N: 5HS1-566), (S/N: 6CS1-543) and (S/N: 7PS1-854) for the D5C only.

1. There is a malfunction in the valve for the speed/direction control.

1. The front hydrostatic pump's POR valve is not set to correct specifications. The rear hydrostatic pump's POR valve is not set to correct specifications.

1. The hydrostatic pumps have too much wear.

1. The crossover relief valves are not set to correct specifications.

Problem

The output of one hydrostatic pump is low.

Probable Cause

1. The hydrostatic pump's charge relief valve is not set to the correct specifications.

1. The hydrostatic pump's POR valve is not set to correct specifications.

1. The hydrostatic pump's crossover relief valves are not set to the correct specifications.

1. There is a malfunction in the valve for the speed/direction control.

1. The hydrostatic pump has too much wear.

Problem

There is no hydrostatic pump pressure in one of the pumps or there is no hydrostatic pump pressure in both of the pumps.

Probable Cause

1. The hydraulic tank is low on oil.

1. The hydrostatic pump's charge relief valve is bad.

1. The hydrostatic pump's charge pump failed.

1. Both hydrostatic pumps have failed or the hydrostatic pump drive has failed.

Problem

The machine moves with the direction/speed control in the NEUTRAL position.

Probable Cause

1. The adjustment that centers the direction/speed control is not set to the correct specifications.

1. The control valve's plunger is sticking.

1. The ball resolver in the pilot control valve is stuck.

1. A pump actuator's neutral position is not set correctly.

1. The control valve's cartridge has a large amount of wear. The plunger has a large amount of wear.

Problem

The machine tracks to the right or the machine tracks to the left when the direction/speed control lever is in the FORWARD and REVERSE position. The speed selector switch is in the SLOW mode.

Probable Cause

The adjustment for the maximum displacement of the right and left drive motors is not equal.

Problem

The machine tracks to the right or the machine tracks to the left when the direction/speed control lever is in the FORWARD and REVERSE position. The speed selector switch is in the FAST mode.

Probable Cause

The adjustment for the minimum displacement of the right and left drive motors is not equal.

Problem

The machine tracks to the right or the machine tracks to the left when the speed/direction control lever is in the FORWARD and REVERSE position. The speed selector switch is in the FAST mode or the SLOW mode.

Probable Cause

1. The adjustment that centers the direction/speed control is not set to the correct specifications.

1. The stops for the maximum displacement and the minimum displacement are not set equally.

1. A resolver ball in the pilot control valve is stuck, dirty or missing.

1. One steering control valve's cartridge has a large amount of wear. The plunger has a large amount of wear.

1. The parking brake is not fully disengaged on one side.

1. There is excessive resistance in one final drive.

1. There is excessive resistance in the track idler, the rollers or the links on one side.

1. A pump actuator's neutral position is not set correctly.

Problem

The machine will not start to move until the engine speed is very high.

Probable Cause

1. The cable for the front hydrostatic pump's speed sensing valve is not properly adjusted.

1. The front pump's charge relief valve is not set to the correct specifications.

1. The adjustment for the speed sensing valve is not set to the correct specifications.

1. The overspeed control valve is not set to the correct specifications. This pertains to (S/N: 5HS1-566), (S/N: 6CS1-543) and (S/N: 7PS1-854) for the D5C only.

1. The linkage for the brake pedal is not set to the correct specification.

1. The linkage for the pilot oil's shutoff valve is not set to the correct specification.

Problem

The machine has low performance. The machine has poor digging. The machine has weak force.

Probable Cause

1. The engine's high idle rpm is not set to the correct specifications.

1. The speed selector switch is in the FAST mode.

1. Engine power is low.

1. The cable for the front hydrostatic pump's speed sensing valve is not properly adjusted or the adjustment for the speed sensing valve is not set to the correct specifications.

1. The adjustments of the POR valves is not set to the correct specifications.

1. The adjustments of the crossover relief valves is not set to the correct specifications.

1. The rear hydrostatic pump's charge relief valve is not set to the correct specifications. This pertains to (S/N: 5HS1-566), (S/N: 6CS1-543) and (S/N: 7PS1-854) for the D5C only.

1. The rear hydrostatic pump's speed sensing valve's adjustment is not set to correct specifications. This pertains to (S/N: 5HS1-566), (S/N: 6CS1-543) and (S/N: 7PS1-854) for the D5C only.

1. The overspeed control valve is not set to correct specifications. This pertains to (S/N: 5HS1-566), (S/N: 6CS1-543) and (S/N: 7PS1-854) for the D5C only.

1. The linkage for the service brake pedal is not set to the correct specification.

1. The linkage for the pilot oil's shutoff valve is not set to the correct specification.

1. The viscosity of the hydraulic oil is incorrect.

1. The specification for the maximum displacement of both motors is not set correctly.

1. Parking brakes not fully disengaged.

Problem

The machine's maximum speed is not set to the correct specification when the speed selector switch is in the FAST mode.

Probable Cause

1. Parking brakes not fully disengaged.

1. There is a problem with the electrical circuit in the speed selector.

1. The adjustment for the minimum displacement of the right and left drive motors is not set to the correct specifications.

1. There is excessive resistance in the final drives.

1. There is excessive resistance in the undercarriage.

Problem

The machine's maximum speed does not change when the speed selector switch is moved from the SLOW mode to the FAST mode.

Probable Cause

1. There is a problem with the electrical circuit in the speed selector.

1. The solenoid for the minimum displacement of the right and left drive motors failed.

Problem

The hydrostatic circuits are erratic.

Probable Cause

1. The oil level is low.

1. The adjustment that centers the direction/speed control is not set to the correct specifications.

1. The pilot control valve's resolver is malfunctioning.

1. The hydraulic oil's temperature is too low. Warm the oil to the correct operating temperature.

1. The hydraulic oil is very dirty.

Problem

If the temperature of the hydraulic oil rises above 99°C (210°F), the polyurethane seals that are in the system will begin to fail. High oil temperature causes the seals to fail more quickly. There are many reasons for the oil temperature to rise.

1. The oil level is low.

1. The oil cooler is restricted. The radiator is restricted.

1. The speed of the cooling fan is too low.

1. The charge relief valves, crossover relief valves, or POR valves are opening at too low oil pressure.

1. There is a restriction in an oil passage. There are too many restrictions in the hydraulic system.

1. The viscosity of the hydraulic oil is incorrect.

1. The load of the hydrostatic system is too high. The load of the implement system is too high.

1. The implement system's settings are incorrect.

1. The hydrostatic pumps or motors have too much wear.

1. There is air in the hydraulic oil.

Note: If there is air in the oil, the problem must be fixed before the system will operate at normal temperature.

1. There are two reasons for air in the oil.

   1. The return oil flows into the tank above the level of the oil that is in the tank.

   1. There are air leaks in the suction line.

1. The oil is very dirty.

1. The oil cooler's bypass valve is stuck open.

1. The coolant's level is low in the radiator.

Thank you for using JustAnswer, if you do need further help, please let me know.
If you are satisfied with my service, please take a moment to provide a rating.
Thanks again, Don
CATMASTERTECH