525D, 535D, 545D and 555D Wheel Skidders Caterpillar

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Escaping fluid under pressure, even a pinhole size leak, can penetrate body tissue, causing serious injury, and possible death. If fluid is injected into your skin, it must be treated immediately by a doctor familiar with this type of injury. Always use a board or cardboard when checking for a leak.

This section provides probable causes to known problems. Since there may be several probable causes, specific inspections or instrument tests may be recommended. These inspections and tests will help to identify the causes that are most probable.

Note: Make sure that you use an oil with the correct viscosity for the operating conditions.

ReferenceFor additional information about the various lubricant viscosities, refer to the Service Manual module Operation and Maintenance Manual, SEBU6250, "Lubricant Viscosities".

System Overview

Brake Manifold

The brake charging manifold is located on the left side of the machine, under the cooling fan. The fan compartment door provides access to this component.

Illustration 1	g03679459
(1) Port "P" (2) Port "A1" (3) Port "A2" (4) Supply Pressure Tap (Port"PG") (5) Port "LS" (6) Brake Accumulator Pressure Tap (Port "PSG") (7) Relief Valve (8) Brake Charge Sensor (9) Brake Charging Valve

The brake charging valve (9) receives oil from the fan hydraulic pump through Port "P" (1) . The relief valve limits pump supply pressure to a specific pressure setting. Supply pressure can be measured at the supply pressure tap (4) in Port "PG" of the brake charging valve.

The brake charging valve (9) contains a priority spool. This spool gives the brake hydraulic system a priority flow over the fan hydraulic system. The brake charging valve also contains a balance spool, which maintains equal pressure at Port "A1" (2) and Port "A2" (3) . The hose attached to Port "A1" directs oil to the following locations: two of the four brake accumulators, the front -brake port of the service brake valve, and Port "DLS" of the front manifold. The hose attached to Port "A2" directs oil to two of the four brake accumulators and to the rear-brake port of the service brake valve.

The brake accumulator pressure tap (6) is installed in Port "PSG" of brake charging valve (9) . This tap can be used to measure brake accumulator pressure. The brake charge sensor (8) also measures brake accumulator pressure. The Machine ECM uses the input from the brake charge sensor to alert the operator when the pressure in the brake system is low.

A shuttle valve in the brake charging valve (9) compares the system pressure requirements of the braking system and of the fan system. The higher of the two pressure requirements is transmitted to the pump control valve through Port "LS" (5) of the brake charging valve.

Brake Accumulators

Four brake accumulators are located in front of the hydraulic tank, on the right side of the machine. The top cover in front of the cab provides access to these components.

Illustration 2	g03679484
(1) Rear Brake Accumulators (2) Front Brake Accumulators

The machine is equipped with two rear brake accumulators (1) and two front brake accumulators (2) . The rear brake accumulators receive oil from Port "A2" of the brake charging valve. The front brake accumulators receive oil from Port "A1" of the brake charging valve.

The cylinder of each accumulator contains a sealed piston. The chamber on one side of this piston is pressured with nitrogen gas. The chamber on the other side of this piston contains hydraulic oil.

Normal Operation

When the engine is operating, the brake charging valve directs hydraulic oil into each accumulator. The pressurized oil in the brake accumulators maintains a consistent supply of oil to the brakes and differential locks, regardless of the demands on the hydraulic pump. These accumulators also ensure that the service brakes can be engaged when the engine is shutoff.

When cut-in oil pressure in the brake accumulators occurs at 11720 ± 345 kPa (1700 ± 50.0 psi), the brake charging valve will increase the pressure at the accumulator. Once the cut-out oil pressure in the accumulators is attained, at 17200 ± 345 kPa (2495 ± 50.0 psi), the brake charging valve will stop increasing oil pressure.

Service Brake Accumulator Faults:

When any brake accumulator pressure sensor diagnostic is active, the operator will experience a loss of service brake pressure. A level 3 warning will be active.

• Service Brake Accumulator Pressure Sensor Diagnostics (CID 1961)

• Service Brake Accumulator Event E284 (3) "Low Brake Accumulator Pressure"

Service Brake Valve

The service brake valve (1) is located under the cab. The cab must be titled to access this component.

Illustration 3	g03679512
(1) Service Brake Valve (2) Inlet Line (for front brakes) (3) Inlet Line (for rear brakes) (4) Return Line (5) Outlet Line (for front brakes) (6) Outlet Line (for rear brakes) (7) Front Brake Pressure Tap (8) Rear Brake Pressure Tap

The service brake valve (1) is controlled by the service brake pedal. The valve provides independent actuation of the front and rear service brakes. The front brake engagement pressure can be measured at the front brake pressure tap (7) . The rear brake engagement pressure can be measured at the rear brake pressure tap (8) .

The inlet line (2) for the front brakes is connected to the front brake accumulators. The inlet line (3) for the rear brakes is connected to the rear brake accumulators. The inlet line (3) for the rear brakes is connected to the rear brake accumulators. The service brake valve (1) is closed-centered. When the service brakes are blocked at the service brake valve. When the service brakes are engaged, oil is sent through outlet line (5) for the front brakes and outlet line (6) for the rear brakes.

Problem List

Problem List for the Service Brakes

1. The front service brakes do not operate, and the warning system is not activated.

2. The rear service brakes do not operate, and the warning system is not activated.

3. Service brakes slip, and the warning system is not activated.

4. Service brakes are not applied evenly.

5. Too much force is needed to push the brake pedals, and the warning system is not activated.

Problem List for the Parking Brake

1. The parking brake does not hold the machine stationary.

2. The parking brake does not engage when the parking brake control knob is pulled out.

Problem List for the Charging System for the Service Brakes

1. The low oil pressure warning will not turn off.

Troubleshooting

Problems with Service Brakes

Problem 1

The front service brakes do not operate, and the warning system is not activated.

Probable causes

1. The brake group within the axle housing is damaged.

2. The lines to the front service brakes are obstructed.

3. The front circuit of the service brake control valve is faulty.

4. The accumulator for the front service brakes is faulty.

5. The accumulator charging valve is damaged.

6. The priority flow control valve is damaged.

7. The piston pump is damaged.

Problem 2

The rear service brakes do not operate, and the warning system is not activated.

Probable causes

1. The brake group within the axle housing is damaged.

2. The lines to the rear service brakes are obstructed.

3. The rear circuit of the service brake control valve is faulty.

4. The accumulator for the rear service brakes is faulty.

5. The accumulator charging valve is damaged.

6. The priority flow control valve is damaged.

7. The piston pump is damaged.

Problem 3

Service brakes slip, and the warning system is not activated.

Probable causes

1. One or both axles contain an incorrect hydraulic oil additive.

2. The brake disc in the axle housing is worn.

Problem 4

Service brakes are not applied evenly.

Probable causes

1. The brake group within the axle housing has air in the hydraulic fluid.

2. The brake disc and associated components in the axle housing are excessively worn.

3. The brake valve is sticking because of contaminated oil.

Problem 5

Too much force needed to push the brake pedal, and the warning system is not activated.

Probable causes

1. The brake pedals and/or brake pedal linkages are damaged.

2. The pump output is too low or the pump output has no pressure.

3. The brake valve is sticking because of contaminated oil.

Parking Brake Problems

Problem 1

The parking brake does not hold the machine stationary.

Probable causes

1. The parking brake must be adjusted.

2. The brake linings are excessively worn.

3. There is grease or oil on the brake drum and/or on the brake lining.

Problem 2

The parking brake does not engage when the parking brake switch is pressed ON.

Probable causes

1. The parking brake valve spool is sticky because of contaminated oil.

2. The parking brake is out of adjustment.

Problem 3

The parking brake does not disengage when the parking brake switch is pressed OFF.

Probable causes

1. There is low hydraulic pressure. Check brake accumulator pressure.

2. The parking brake valve spool is sticky due to contaminated hydraulic oil.

3. The coil on the parking brake control valve is bad.

Problems of the Charging System for the Service Brakes

Problem

The low oil pressure warning will not turn off.

Probable causes

1. There is inadequate pump pressure for the brake system.

   Note: If you can turn off the warning by increasing the rpm of the engine, the cause of the problem is the brake pump.

2. The hydraulic oil is too hot.