CB-534C and CB-634C Vibratory Compactors Propel System Caterpillar

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Sudden movement of the machine or release of oil under pressure can cause injury to persons on or near the machine. To prevent possible injury, perform the procedure that follows before testing and adjusting the power train.

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Personal injury can result from hydraulic oil pressure and hot oil. Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system. Make sure all of the attachments have been lowered, oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.

Operational Checks

Note: The checks during operation can be used to find leakage in the system. These checks can also be used to find a bad valve, a bad pump, or a bad motor. Travel speed can be used to check the condition of the propel motors and the pump.

Operate the machine in each direction and in all speeds.

• Watch the drum and the wheels.

• Starting and stopping operations should be progressive.

• The drum and the wheel rotation should be normal at all times.

• Check for noise from the pump and drive motors.

• Check for the sound of the relief valves that are opening. The opening pressures of the relief valves are given in Propel Pump Relief Valve - Test and Adjust and Charge Relief Valve - Test and Adjust of this module.

• After you select the travel speed of the compactor, the forward and reverse motion should be identical.

Probable Causes of Problems in the Propel System

Problem

The propel system engages very slowly when the operator is attempting to shift.

Probable Cause

• Low charge pressure.

• The orifices in the propel pumps are plugged.

• The oil is too viscous and/or the oil is too cold.

• The charge filter is plugged.

• The hydraulic oil level is low.

• The control valve is malfunctioning.

Problem

The propel system engages very suddenly when the operator is making a shift.

Probable Cause

• The orifices are missing from the propel pumps.

• The shuttle valve spool that is inside the flushing valve is sticking.

• The servo valve spool is sticking.

Problem

The propel system operates in one direction only.

Probable Cause

• The pump servo valve has failed .

• The pump servo piston has failed.

• The rocker arm section of the pump swashplate assembly has failed.

• One of the multifunction valves is damaged.

• The shuttle valve spool is sticking.

• The control valve has failed.

Problem

The propel system does not disengage when the propel control lever is returned to neutral.

Probable Cause

• The pump servo valve has failed .

• The pump servo piston has failed.

• The rocker arm section of the pump swashplate assembly has failed.

• The neutral adjustment of the servo valve is incorrect.

• The linkage rod between the propel pump controls has an incorrect adjustment.

Problem

The parking brake does not release when the parking brake button is pulled up.

Probable Cause

• The parking brake button has failed.

• There is a malfunctioning piston seal in the brake group.

• The parking brake valve has failed.

• There is a fault in the electric circuit.

• The neutral start switch has failed.

• Low charge pressure.

• The brake relay has failed.

• The steering pump relief valve is damaged or incorrectly adjusted.

• Failure of the steering pump.

Problem

The parking brake does not engage when the parking brake button is pushed down.

Probable Cause

• The parking brake button has failed.

• The brake relay has failed.

• The brake discs are worn.

• There is a pinched brake line.

• The parking brake valve has failed.

• There is a fault in the electrical circuit.

Problem

There are external oil leaks from either of the propel motors.

Probable Cause

• Motor case pressure is too high.

• There is a restriction in the oil return line to the hydraulic oil tank.

• There are damaged seals due to pressure peaks, use of unapproved hydraulic oil, or an incorrect tightening torque.

Problem

The oil in the propel system overheats.

Probable Cause

• An incorrect type of oil is used in the hydraulic circuit.

• The oil cooler is internally restricted.

• The radiator and/or the oil cooler is externally restricted.

• There is a low charge line pressure that is caused by excessive internal leakage in the circuit.

• The operating pressures are exceeding the relief pressures due to mechanical problems.

• The thermal bypass valve has a malfunction.

Problem

Low charge pressure (Neutral).

Probable Cause

• The hydraulic oil level is low.

• The charge filter in the propel system is in the bypass mode.

• The high idle of the machine is too low.

• There is an inadequate flow of oil from steering pump.

• There is excessive leakage from the motor case.

• There is excessive leakage from the pump case.

• The seal on the parking brake is leaking.

Problem

Low charge pressure (Propelling).

Probable Cause

• There is excessive leakage from the motor case.

• There is excessive leakage from the pump case.

Problem

The driven drum slips during propelling.

Probable Cause

• The friction is not gripping the inner race of the bearing due to excessive wear or contamination of the grease.

• The radial runout between the halves of the drum is too large.