Er...do Accumulator spheres only work going forwards?

[Jaf]

I reversed the other day with the engine off, the brakes didn't work at all. Thought the Accumulator sphere was shot but tested again when going forwards and the brakes worked long enough for me to get bored. Is this normal? Ta.

[aerodynamica]

Hi, the accumulator will hold a reserve of pressure for the brakes with the engine off whether it's rolling back or forward. I'm struggling to think of a reason for the phenomenon you experienced though.

If the accumulator is shot there will be no brake pressure reserve after the engine goes off except for the pressure stored in the 'anti sink' accumulator sphere located in the middle of the rear axle. This however only serves the back brakes but they should still work even if the main accumulator is flat. Though if both accumulators are dead and the engine is off there'll be nothing for the brakes!! Handbrake will still work on the front wheels though (last resort)

You didn't say if you had switched the engine on again before testing the brakes going forward. If so that might have topped up the pressure and that's why the brakes worked and going forward was just a coincidence.

If your accumulator is good you can demonstrate it by running the engine and then switching off. Next move the suspension height lever up to the next height and it should raise up the suspension with the engine off (at the least the back suspension should go up). If there's nothing then the accumulator is dead. A second test is to run the engine, press the foot brake repeatedly. You should be able to press it about 7-8 times before the pressure regulator clicks (should hear it even with the engine running). If you hear the click sound as soon as the brake is pressed then there's no reserve in the accumulator.

Can also check by switching off the engine and then with a 12mm spanner slacken the 12mm bolt on the pressure regulator (the accumulator is attached to it) - just loosen it by a turn - dont remove it- and as you do there should be the sound of a long whooosh noise as the accumulator enpties. If you dont hear it the thing is flat.

There are a lot of signs of a flat accumulator sphere. Also if you raise the suspension up with the engine running the click of the pressure regulator should be at most once every 5 seconds as the suspension raises. If it clicks frequently like more than once a second then again, a sign the sphere is flat.

Let us know what the car does!

[xantia_v6]

There is also the rear brake accumulator sphere (commonly and wrongly called the anti-sink sphere). For you to have no brakes, both the main accumulator and rear brake accumulator spheres must be discharged.