Brakes hissing noise advice please

[ToneyCaroney]

Hi All,

Out in the Griff today and it has started making a hissing noise when pressing the brake pedal.sounds like air escaping from something. Pedal also seems to need a bit more pressure applied. If I press the pedal with engine off it firms up as usual and servo kicks back in ok after starting but hissing returns.

Cheers.

Edited by ToneyCaroney on Sunday 26th February 15:36

[MikeE]

Sounds like it's terminally ducked, better trade it for that Exige first thing tomorrow!!

[ToneyCaroney]

Thanks Mike. Sage advice as normal

[MikeE]

I'm only telling you what you want to hear

[roseytvr]

You want to hope there's an air leak in the vacuum pipe going to the servo. Unfortunately more likely you have punctured the diaphragm in the servo. These are getting hard to find and are quite expensive, even worst you need to be a contortionist to change it. Could also be the master cylinder on its way out. Are you loosing any brake fluid?

[ClassicChimaera]

Try and feel the underside of the servo, if it's very rusty it could be fubbered.

[Matthew Poxon]

I had the exact same issue on mine.

This was the cause:

[ClassicChimaera]

Matthew Poxon said:

I had the exact same issue on mine.

This was the cause:

and that's very very rusty. Had you been on track with this Matthew?

[ToneyCaroney]

Thanks all,

So I had a nose around this morning and the I don't seem to be losing brake fluid - reservoir is still a few mm from the top. I've looked a the servo as best I can by crawling into the footwell. It looks to be in good condition (apart from a bit of yellow gunk that seems to have been brushed on). Feeling around it (as much as I can get too) it feels solid and surface is smooth, i.e no rust. No brake fluid leaks into footwell either.

Pic of (part) servo.

[5.0ltr]

Can you get someone to operate the pedal while you listen to the servo surround? Hissing suggests air, its the servo diaphram or a pipe connected thereabouts I would imagine.

[ToneyCaroney]

I can give that a go but won't I need my head right next to the pedals!? Or, is there another way to get near the servo? Cheers.

[TwinKam]

Stethoscope, ie a couple of metres of eg screenwash pipe, stick an end in one ear and wave the other end in the direction of the servo.

[ToneyCaroney]

Update on this for anyone else who might have the same: was indeed the servo itself. Now replaced along with master cylinder as a precaution and all is well.
Cheers to all (not Mike!) for the helpful suggestions

[Matthew Poxon]

Glad you sorted it and good move replacing the cylinder at the same time, makes sense while the servo is out.

[MikeE]

ToneyCaroney said:

Update on this for anyone else who might have the same: was indeed the servo itself. Now replaced along with master cylinder as a precaution and all is well.
Cheers to all (not Mike!) for the helpful suggestions

You're so ungrateful!!