brake hiss

[adw555]

Had my brake fluid changed last week (the 2 year thingy) and while sitting in a queue of traffic tonight I can hear a hiss every time I pressed the brake pedal while stationary....is this normal?..never noticed it before, and maybe cos I'm looking out for brake problems after the poor car had the visit to a dealer.

[Teutonic_Tamer]

You've got a snake on the loose !!!  

Seriously, it sounds like the brake servo.  The servo will "vent" the stored vacuum as you press further on the brake pedal.  Even if you think you are holding the brakes perfectly "constant", it is very difficult to actually hold the pedal in a fixed position, unless you are actually trying to do so.

Does the brake pedal sink to the floor under constant pressure?

Does the vacuum in the servo correctly build up?  (if you dont know how to check this, let me know, and I'll post the simple details).

[adw555]

Hi TT,

No it doesnt sink right to the floor..I suppose if I press hard enough it goes down half way..

I'm not sure what you mean about the servo vaccum building up ?...I know if I turn the car off and pump the pedal a couple of times it goes rock hard..

[Teutonic_Tamer]

Hi TT,

No it doesnt sink right to the floor..I suppose if I press hard enough it goes down half way..

OK, thats good.

I'm not sure what you mean about the servo vaccum building up ?...I know if I turn the car off and pump the pedal a couple of times it goes rock hard..

Right, that's also good.  Now, with the engine off, and after you have pumped the pedal a few times, so that it goes hard (oo-er, misus!) - keep your foot pressed hard on the brake pedal, and then start the engine.  The pedal sould sink a little as the vacuum builds up again.