Hissing noise

[boohicks]

Hi I have a Ford Galaxy (2000 plate) with a hissing noise coming from the brakes, the car isn't loosing power and brakes fine, does this mean that the brake servo needs replaced? could anyone explain how to do this?? thanks     

[BioDiesel]

If the noise is inside the cabin near the brake pedal, then yes it does sound like a leaky servo.
Does the noise change when you apply the brakes ?
Does the noise gradually die away when you stop the engine ?

A good way of pinpointing the source of the hiss is to use a stethoscope, or if you don't happen to have one lying around, a length of pipe - put one end near your ear and the other at the suspect hiss generator - it works well.

[steveo59]

Hi Boohicks,
As Biodiesel says, if you cut a metre length of garden hose, hold one end to your ear and move the other end about where you suspect the hissing noise to be coming from, when you get to the right place the noise will get louder. As well as from the brake servo, if the noise is in the engine bay it could be a vacuum leakfom one of the pipes connected to the inlet manifold,air leaner,turbo etc.

[Mirez]

Also worth checking if its inside the cabin, that its not the vacuum system for the cruise control as the pipework is down at the clutch and brake pedals.