Testing the brake accumulator is a very simple. Anyone can do it, no mechanic needed.

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These tests should be done in a quiet environment so you can hear the brake pump run. Turn off  the radio, A/C and anything else in the car that makes noise.

Test number 1

The purpose of this test is to see how many pumps of the brake pedal it takes to get the red brake warning light to come on. The higher the number the better. A new accumulator will be about 7 pumps and a shot accumulator would be 1 pump.

1. Turn on the key (don't start the engine).
2. Wait for the red and yellow brake warning lights to go out and a few seconds later you will hear the pump stop running.
3. Rapidly pump the brake pedal about 4 times while watching to see if the red brake warning light comes on.  If it does, wait for the pump to build up pressure again. The light will go out and the pump will stop.
4. Then pump the brake pedal 3 times to see if the red light comes on.

-Jim Finn

Test number 2

This test will help verify the results of the first test.

1. Open the hood so you can hear the brake pump motor run.
2. Turn the key ON ... (Don't start the engine).
3. Listen to the brake pump running and wait until it stops.
4. Push the brake pedal like you are making a normal stop. Release and push the pedal again until you hear the brake pump start.

• A bad accumulator will cause the brake pump to run each time you press the brake pedal.
  *The pump running so much could cause damage to the pump over time.
• A good accumulator might give you up to 5 pedal pumps before the brake pump starts.
  *Other factors, like air in the brake system, can cause you to get less pedal pumps even if the accumulator is new.
  

-Barney Eaton

If you get inconsistent results when repeating the test above, it may be because the pressure switch is going bad. Jim Finn suggests pulling the pressure switch electrical connector and looking for moisture inside. If it is damp inside the connector, brake fluid is leaking past the seals and the switch is failing.

Test number 3

 This test will also give you an indication of the condition of the accumulator.

1. Clean the side of the brake fluid reservoir so you can see the fluid level.
2. Put a piece of masking tape on the side of the reservoir so you can mark the fluid level.
3. With the key OFF... pump the brake pedal until it gets hard.
4. Mark the level of the brake fluid in the reservoir. It should be to the full mark.
   

   If the fluid level is near the cap there is too much fluid in the reservoir. Remove any excess fluid before marking the tape.

5. Turn the key ON and wait until the brake pump stops (the amount of time it takes for the pump to stop is also a clue, very short or very long run time is bad).
6. When the pump stops, mark the fluid level on the tape and measure the difference between the two marks. The amount of fluid reflects the amount of fluid going into the accumulator.

*If the fluid level change is 1/2 inch or less, your accumulator is probably in good working order. If the fluid drops 5/8 inch or greater your accumulator may be on its last legs.

*A totally defective accumulator will give a zero, or almost zero, drop in the fluid level in the reservoir. An accumulator with a ruptured diaphragm will lose the factory pre-charge and it will not displace fluid so the fluid level will stay the same.

 -Barney Eaton

Thanks to members of the Reatta forums, for this information.