Brake System Pressure Test

The pump flow and pressure tests will confirm or rule out the pump as the cause of brake system problems.

Prior to performing the pump flow and pressure test, perform the Hydraulic Leak Test as described in this section.

If all preliminary items are to specifications, or have been corrected, and the loss of assist still exists, test the brake pump flow and pressure to determine whether the trouble is in the pump, the Hydro-Max booster, the HR-1 valve, the plumbing or the pressure relief valve, as follows:

Preparation for Hydraulic Pressure/Flow Tests

The power steering analyzer is to be used when the brake system is suspected of erratic operation or insufficient power assist, and the pump does not exhibit sustained failure or internal damage that may contaminate the fluid in the system. Rotunda Truck Medium/Heavy Duty Power Steering System Analyzer 014-00230 consists of a pressure gauge, flow meter, shutoff valve, thermometer, hose and adapter attachments.

Possible contamination of the system fluid may cause permanent damage to gauges and instruments incorporated in the analyzer. If there is a possibility of burned fluid or metal particles in the fluid, the brake system should be purged before connecting the power steering analyzer.

Refer to equipment instructions for installation diagrams and torque specifications.

1. To connect the analyzer into the brake system, disconnect the pressure line from the connector at the gear, pump or lines, as indicated in the hookup diagrams.

2. Thread M-16 Adapter D85T-33610-A or equivalent to the connector and insert in gauge pressure line.

3. Connect the analyzer to the adapters and tighten. Be sure the analyzer line at the shutoff valve end is connected to the pump of the vehicle brake system as indicated in hookup diagram.

4. Fully open the shutoff valve, start engine and purge the air from the brake system by applying the brakes several times. Shut off engine and check connections for leaks.

5. Check for proper fluid level at reservoir and add or remove fluid as required. Recheck for air in the system by restarting engine, partially close the shutoff valve and view the pressure gauge. If the gauge needle vibration is excessive, too much air remains in the system. Repeat Step 4 to purge any remaining air from the system.

6. Install thermometer provided with analyzer in the reservoir and connect tachometer to the engine.

Hydraulic Pressure/Flow Test Procedure

1. Check brake system back pressure as follows:

   1. Fully open the analyzer shutoff valve.
   2. Start engine and run at 2,000 rpm.
   3. When fluid temperature reaches 55°C (130°F), record flow and pressure.
      • If flow is below 11.7 lpm (3.1 gpm), check to see if correct pump is installed for the vehicle being tested. If correct pump is installed, continue testing to find problem.
      • If pressure exceeds 172 kPa (25 psi), check lines for kinks or obstructions. If none are found and pressure remains high, continue testing to find problem.

2. Check pump for minimum efficiency flow.

   1. Decrease engine speed to 800 ± 50 rpm.
   2. Slowly close the shutoff valve to build pressure to 8400 kPa (1200 psi).
   3. Record flow with temperature at 55°C (130°F) or above.
   4. If flow is below 5 lpm (1.3 gpm), check if correct pump is installed for vehicle and equipment being tested. Pump may require repair or replacement, especially if flow in Step 1 was also below value indicated.

3.  CAUTION: Do not hold the valve closed for more than five seconds. Failure to follow this caution will result in damage to pump.

   Check pump for pressure relief valve operation as follows:

   1. Run engine at 800 ± 50 rpm.
   2. Completely close and partially open the shutoff valve three times.
   3. READ pressure when valve is fully closed.
   • If pressure is below 8480 kPa (1230 psi), clean or replace pressure relief valve.
   • If pressure reading exceeds 9307 kPa (1350 psi), clean or replace pressure relief valve.
   • If flow/pressure checks are within specifications, the pump is operating normally and other areas should be investigated.