Brake Fluid Accumulator: Testing and Inspection

ACCUMULATOR PRECHARGE CHECK

NOTE:
^ Numbers in parentheses ( ) in procedure below refer to numbers in illustration.
^ The diaphragm type accumulator is precharged with nitrogen at 80 bar, its function is to store hydraulic energy. Over a period of years, a normal loss of precharge will occur.
^ This procedure will indicate the extent to which precharge pressure has fallen.
^ A new accumulator at 20°C (76°F) has a nominal pressure of 80 bar.
^ Minimum acceptable pressure is 50 bar.

PROCEDURE
1. Disconnect battery negative lead.
2. Switch off ignition.
3. Operate the brake pedal 30 times. Pedal travel will increase slightly and reduced resistance will be felt as pressure decreases.
4. Wait for 60 seconds, press the brake pedal four more times. This procedure will ensure that all pressure is evacuated from the system.
5. Remove 3 nuts securing pump/motor assembly to valance. Raise assembly from mounting to allow clearance for pressure test adaptor.
6. Remove banjo bolt (3) securing high pressure hose to pump. Collect sealing washers.
7. Connect pressure gauge (4) to pump using tool No. LRT-70-001, or equivalent, through high pressure hose union.

NOTE: Use original sealing washers.

8. Switch ignition on. Observe pressure gauge.





9. Pressure will rapidly rise to the accumulator precharge value, point X, at which point rate of increase will reduce as pressure rises to system pressure of approximately 170 bar.
10. With a new accumulator, point X will occur at 80 bar.
11. Renew accumulator if point X occurs below 50 bar.
12. Depressurize system. Remove test equipment.
13. Using new sealing washers, position high pressure hose to pump. Secure with banjo bolt. Tighten to 24 Nm (18 ft. lbs.).
14. Align pump/motor assembly to mounting. Secure with nuts. Tighten to 8 Nm (6 ft. lbs.).
15. Bleed brake system. Brake Bleeding