Brakes: - Does your brake pedal hiss at you?

ww1dm1 · Apr 18th, 2016, 11:26

One thing that annoys me on my V40 is that every time I press the brake pedal it makes a hissing sound inside, exactly as if I'm pressing on a damn foot pump or something. It can also be heard with the bonnet up, near the vacuum booster. The pedal is also kind of spongy, top part of the pedal travel gives little braking. And this sponginess corresponds with the noise, noise occurs in the weak part. All of this is only when the engine is on and the power brakes are working, when the engine is off the pedal hardens up properly after a couple of pumps (also accompanied by hisses). No hissing when pedal returns as well (though a little different more silent noise does exist, as if it's sucking), only during the press in. I bled the lines recently along with a brake fluid change and nothing changed, really.

So I've been wondering, is this just the way the power brake system is designed or is my vacuum booster diaphragm leaky or something? Is your pedal rock hard?

skyship007 · Apr 18th, 2016, 11:57

Unless you have snakes in the footwell, something is leaking. Try getting someone to pump the brakes whilst you listen to the connections from the vacuum system to the master cylinder. Master cylinder faults are rare and the V40 has typical saloon car feel to its brakes. Wild guess but a small leak in a vacuum line connection to the booster would be my guess.

ww1dm1 · Apr 18th, 2016, 15:59

Quote:

Originally Posted by skyship007

Unless you have snakes in the footwell, something is leaking. Try getting someone to pump the brakes whilst you listen to the connections from the vacuum system to the master cylinder. Master cylinder faults are rare and the V40 has typical saloon car feel to its brakes. Wild guess but a small leak in a vacuum line connection to the booster would be my guess.

If there was a vacuum leak I'd think the hiss would be constant and probably accompanied by a hardened brake pedal. In my case the hiss occurs only when the pedal is traveling down and the pedal is squishy. I'll have to listen where exactly the source is, if you say that there shouldn't be any noise.

skyship007 · Apr 18th, 2016, 16:04

Quote:

Originally Posted by ww1dm1

If there was a vacuum leak I'd think the hiss would be constant and probably accompanied by a hardened brake pedal. In my case the hiss occurs only when the pedal is traveling down and the pedal is squishy. I'll have to listen where exactly the source is, if you say that there shouldn't be any noise.

Umm, it does not sound like booster trouble as the pedal would go hard, but the amount of vacuum used will vary, which is why it sounds like a small intermittent leak. Post a recording to You tube, just in case it's a turbo fault plus incorrect bleeding.

More info about hissing brakes:
https://www.yourmechanic.com/service...sed-inspection

druid · Apr 18th, 2016, 16:23

Hows your cruse? There is a vacuum system there as well. I think you would have noticed the brakes failing or "fading" but the cruse maybe not.

druid · Apr 18th, 2016, 16:42

Found this thread and the 2nd post shows a photo of the peddle box whith the vacuum thingy

http://www.volvoforums.org.uk/showthread.php?t=179017

ww1dm1 · Apr 18th, 2016, 17:25

Quote:

Originally Posted by skyship007

Umm, it does not sound like booster trouble as the pedal would go hard, but the amount of vacuum used will vary, which is why it sounds like a small intermittent leak. Post a recording to You tube, just in case it's a turbo fault plus incorrect bleeding.

More info about hissing brakes:
https://www.yourmechanic.com/service...sed-inspection

I wouldn't call it intermittent, as it occurs reliably and every time I press the brake pedal, as long as the engine is running. It's most definitely got nothing to do with the turbo, sounds like a loud and clear whoosh whenever I press the pedal. Exactly like a foot pump. I can try to record the sound if it helps.

The link you provided mostly addresses constant hissing, which would definitely indicate vacuum leaking. The "damaged foam silencer" could be relevant, though. As I understand most power brake systems release air from the vacuum booster whenever the pedal is pressed. Though I haven't ever heard it being so loud on any other car, there is usually a foam filter/silencer to mute that, maybe it's missing. The spongy pedal doesn't help as well, not sure if it's related, though.

Quote:

Originally Posted by druid

Hows your cruse? There is a vacuum system there as well. I think you would have noticed the brakes failing or "fading" but the cruse maybe not.

Cruse, cruse... cruise control? Non-existent, unfortunately. Though I'll check if the vacuum thing is there.

happy diver · Apr 18th, 2016, 19:41

The pneumatic sound is perfectly normal, stop listening for it and it will go away or take off the exhaust.

The web site is advertising a service, they want your money
however at least they they have included this

THE HISSING NOISE YOU HEAR WHEN THE BRAKE PEDAL IS DEPRESSED COULD BE NOTHING MORE THAN ORDINARY OPERATION

COULD, to maintain your interest in their service

You have included all this in your post

"The link you provided MOSTLY ADRESSES CONSTANT HISSING, which would definitely indicate vacuum leaking. The "damaged foam silencer" could be relevant, though. As I understand most power brake systems release air from the vacuum booster whenever the pedal is pressed. Though I haven't ever heard it being so loud on any other car, there is usually a foam filter/silencer to mute that, maybe it's missing. The spongy pedal doesn't help as well, not sure if it's related, though."

Completely omitting the ORDINARY OPERATION bit.
Just as they designed

The only time you're going to have a hard pedal with these systems is when the car is turned off.

skyship007 · Apr 18th, 2016, 19:48

Never heard any type of hiss from my brakes and no one else has mentioned hearing such a noise. Perhaps the OP has a phase one with different sound insulation, or even a different engine.

happy diver · Apr 18th, 2016, 21:42

I call it a brief pneumatic sound and then it is supposed to stop
when the pressure on either side of the diaphragm is equalised.

May be a torn diaphragm but that's just inventing problems where none exist

I like your insulation, or a rotten silencer, idea.

I've got hissing and there's definitely zero problem with my brakes
as many a pushy pedestrian will attest

Apr 18th, 2016, 11:26	#1
ww1dm1 What is this I don't even Last Online: Aug 31st, 2017 08:01 Join Date: Mar 2015 Location: *	Does your brake pedal hiss at you? One thing that annoys me on my V40 is that every time I press the brake pedal it makes a hissing sound inside, exactly as if I'm pressing on a damn foot pump or something. It can also be heard with the bonnet up, near the vacuum booster. The pedal is also kind of spongy, top part of the pedal travel gives little braking. And this sponginess corresponds with the noise, noise occurs in the weak part. All of this is only when the engine is on and the power brakes are working, when the engine is off the pedal hardens up properly after a couple of pumps (also accompanied by hisses). No hissing when pedal returns as well (though a little different more silent noise does exist, as if it's sucking), only during the press in. I bled the lines recently along with a brake fluid change and nothing changed, really. So I've been wondering, is this just the way the power brake system is designed or is my vacuum booster diaphragm leaky or something? Is your pedal rock hard? Last edited by ww1dm1; Apr 18th, 2016 at 12:32.

Apr 18th, 2016, 11:57	#2
skyship007 Premier Member Last Online: May 2nd, 2018 08:14 Join Date: Sep 2011 Location: DownSouth	Unless you have snakes in the footwell, something is leaking. Try getting someone to pump the brakes whilst you listen to the connections from the vacuum system to the master cylinder. Master cylinder faults are rare and the V40 has typical saloon car feel to its brakes. Wild guess but a small leak in a vacuum line connection to the booster would be my guess. __________________ 2003 V40 1.9TD Mods: Scratches, bent bumpers, raised REAR mats & internal mud guards. SHELL ULTRA 5/40 & LIQUI MOLY CERATEC. Everyone should DYOR (Do Your Own Research) Last edited by skyship007; Apr 18th, 2016 at 12:02.

Apr 18th, 2016, 16:23	#5
druid V40 Owner Last Online: Dec 13th, 2020 01:28 Join Date: Aug 2006 Location: Tonyrefail, Souh Wales. View Photos By: druid	Hows your cruse? There is a vacuum system there as well. I think you would have noticed the brakes failing or "fading" but the cruse maybe not. __________________ *An MS Warior living one day at a time* "Neville" 207,000 so far. Water use 0 - oil negligible....

Apr 18th, 2016, 16:42	#6
druid V40 Owner Last Online: Dec 13th, 2020 01:28 Join Date: Aug 2006 Location: Tonyrefail, Souh Wales. View Photos By: druid	Found this thread and the 2nd post shows a photo of the peddle box whith the vacuum thingy http://www.volvoforums.org.uk/showthread.php?t=179017 __________________ *An MS Warior living one day at a time* "Neville" 207,000 so far. Water use 0 - oil negligible....

Apr 18th, 2016, 19:41	#8
happy diver Active Member Moment Last Online: Apr 29th, 2023 05:58 Join Date: Jul 2012 Location: Brisbane: perfect for one day, asleep the rest	The pneumatic sound is perfectly normal, stop listening for it and it will go away or take off the exhaust. The web site is advertising a service, they want your money however at least they they have included this THE HISSING NOISE YOU HEAR WHEN THE BRAKE PEDAL IS DEPRESSED COULD BE NOTHING MORE THAN ORDINARY OPERATION COULD, to maintain your interest in their service You have included all this in your post "The link you provided MOSTLY ADRESSES CONSTANT HISSING, which would definitely indicate vacuum leaking. The "damaged foam silencer" could be relevant, though. As I understand most power brake systems release air from the vacuum booster whenever the pedal is pressed. Though I haven't ever heard it being so loud on any other car, there is usually a foam filter/silencer to mute that, maybe it's missing. The spongy pedal doesn't help as well, not sure if it's related, though." Completely omitting the ORDINARY OPERATION bit. Just as they designed The only time you're going to have a hard pedal with these systems is when the car is turned off. __________________ 20,000 leagues under the sea diving to adventure in a silent world with my ceiling the waves...Emile

Apr 18th, 2016, 19:48	#9
skyship007 Premier Member Last Online: May 2nd, 2018 08:14 Join Date: Sep 2011 Location: DownSouth	Never heard any type of hiss from my brakes and no one else has mentioned hearing such a noise. Perhaps the OP has a phase one with different sound insulation, or even a different engine. __________________ 2003 V40 1.9TD Mods: Scratches, bent bumpers, raised REAR mats & internal mud guards. SHELL ULTRA 5/40 & LIQUI MOLY CERATEC. Everyone should DYOR (Do Your Own Research)

Apr 18th, 2016, 21:42	#10
happy diver Active Member Moment Last Online: Apr 29th, 2023 05:58 Join Date: Jul 2012 Location: Brisbane: perfect for one day, asleep the rest	I call it a brief pneumatic sound and then it is supposed to stop when the pressure on either side of the diaphragm is equalised. May be a torn diaphragm but that's just inventing problems where none exist I like your insulation, or a rotten silencer, idea. I've got hissing and there's definitely zero problem with my brakes as many a pushy pedestrian will attest __________________ 20,000 leagues under the sea diving to adventure in a silent world with my ceiling the waves...Emile

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)