servo / master cylinder leak.
Turbo Mini Forums

Hi
I noticed an air leak sound when I press the brakes, narrowed it down to between the master cylinder and servo body. The brakes arent bled yet, so still air in the system. Is this normal / will it go when the brakes are bled?

I'm doing a big minispares order, so wondered if there is a gasket I may need etc before I hit the button.

Thanks, James.

The brake servo stores vacuum from the inlet manifold. When you depress the pedal, one side of the diaphragm is exposed to atmospheric pressure while the other is exposed to the vacuum. this gives the servo assistance. as a result, when the vacuum is released to expose the diaphragm to atmospheric pressure, you will hear what sound like air escaping. but it should only be momentary each time the pedal is depressed. If it is constant, the diaphragm may be ruptured.

Since the servo stores a certain amount of vacuum, you will still have this servo assistance for a coupl or more pedal depresses, with the engine switched off, until the vacuum is depleated. The pedal then starts to go 'hard'

test the operation of the servo, with the engine off, depress the brake pedal several times to deplete any stored vacuum. Then, press firmly on th brake pedal and start the engine. The pedal should move towards the floor showing that the servo is functioning correctly. Obviously you need to do this when the brakes have been blead properly, but in any case, if you havent already you should do so, before asking for help on whether something is wrong or not. Makes sense?