Hi, I have a gas 2011 Winnebago on a Ford Chassis. When the engine is running and I press the brakes hard, even if I'm stopped, the brakes hiss. The sound seems to be coming from the area of the pedal. Lightly pressing doesn't cause a hiss.Is this normal? I asked the shop that I usually have work on my RV, and they said it is, but I'm not convinced that they actually heard the sound. The tech originally said it's the emergency brake pump that comes on if the engine is off, but this happens when the engine is on, so it's not that. Plus, I wouldn't describe that pump as anything like a hiss. When I pointed this out to him, he said, oh, that's normal then, it's the vacuum for the cruise control. (I like the shop, but they're kind of strange in that sometimes I have to convince them to fix something, so I don't trust them saying it's normal. I've had some funny conversations that have ended with me saying, "You do realize that I'm going to pay you to do this work, don't you?" But, their work has always been good once I convince them to work on something, and I feel that they are honest.)Thanks.

possibly a snake crawled up there. No seriously there is some type of piston that expels air when you push or release the pedal. maybe has something to do with vaccum assist system

Find a new shop if the current one does't want to find thee problem. It sounds like a vacuum leak to me.

Your F53 has a hydroboost pump to assist braking. It doesn't have a vacuum system.The hydroboost should work full time so you'll still have brakes if you should ever lose power (or ignition power fails). The idea is for you to have full braking power to stop no matter what.Your probably hearing the boost pump running, as it will even under light peddle pressure.

Corkey05 wrote:Your F53 has a hydroboost pump to assist braking. It doesn't have a vacuum system.The hydroboost should work full time so you'll still have brakes if you should ever lose power (or ignition power fails). The idea is for you to have full braking power to stop no matter what.Your probably hearing the boost pump running, as it will even under light peddle pressure.Right on the button. This will concern new owners of ford chassis MH until they find out what it is and how it is designed to work.

wildmanbaker wrote:Corkey05 wrote:Your F53 has a hydroboost pump to assist braking. It doesn't have a vacuum system.The hydroboost should work full time so you'll still have brakes if you should ever lose power (or ignition power fails). The idea is for you to have full braking power to stop no matter what.Your probably hearing the boost pump running, as it will even under light peddle pressure.Right on the button. This will concern new owners of ford chassis MH until they find out what it is and how it is designed to work.Ya but that sound is not a hiss its more like a growl

Hissing brakes, is it normal? | Good Sam Community

CG_Dawson
Explorer
Feb 18, 2016
In the final analysis I really think you will find that Corky nailed it in his first response. It's the pump and it's normal.
wildmanbaker
Explorer
Feb 17, 2016
4mat, you seem pretty sure of what it is not, maybe you should remove the inside engine cover and apply the brakes to try and isolate the sound. Have you verified you have the correct level in the hydraulic system reservoir? This could be what is making the hissing sound, as there is no vacuum connections to the brake system or the brake pedal.
Cloud_Dancer
Explorer II
Feb 17, 2016
WAG
There's 6,391 things that a shop should know (collectively). But, they only know about 3,009. What they don't know they try to learn on the job, or tell you it's normal, or send you to a specialist.
I never expect them to know everything. It's just not possible.
I'm glad I found somebody to buy Advance Automotive 6836 Gateway East El Paso TX.
Corkey05
Explorer
Feb 17, 2016
Gallifrey wrote:
I'm pretty familiar with the sound of the booster pump and, as some of you have described it, it's more of a growl than a hiss. It's easy to identify because it runs if the engine is off, where it sounds pretty loud.

This is definitely a hiss. A hiss like a punctured basketball, air escaping from a tire, a ticked off cat, a punctured space ship, etc... It's a pure hiss without any machine sound behind it (besides the normal engine running noise).

Thanks for all the ideas so far. (To the person who suggested I find another mechanic, feel free to point one out to me in my area, but, in the meantime, I'm happy I found an honest shop that does good work, even if I have to push them sometimes. My question here will help me decide if I should push this sound as something they need to look in to.)
Is it possible you're hearing a vacuum leak from your HVAC system?
Gallifrey
Explorer
Feb 17, 2016
I'm pretty familiar with the sound of the booster pump and, as some of you have described it, it's more of a growl than a hiss. It's easy to identify because it runs if the engine is off, where it sounds pretty loud.

This is definitely a hiss. A hiss like a punctured basketball, air escaping from a tire, a ticked off cat, a punctured space ship, etc... It's a pure hiss without any machine sound behind it (besides the normal engine running noise).

Thanks for all the ideas so far. (To the person who suggested I find another mechanic, feel free to point one out to me in my area, but, in the meantime, I'm happy I found an honest shop that does good work, even if I have to push them sometimes. My question here will help me decide if I should push this sound as something they need to look in to.)
barmcd
Explorer
Feb 17, 2016
That's your power brake assist leaking. I had one and it literally sounded like someone puffing up and blowing every time I hit the brakes. It was a fairly cheap replacement and only four bolts held it on to the fire wall and another four bolts held on the master cylinder.
Kayteg1
Explorer II
Feb 17, 2016
I have hydraulic boost on my trucks and when you press the pedal hard, you will hear the pump working harder under the load. Same when I turn the steering wheels to the end stops.
Do they really make emergency hydraulic pumps on newer vehicles, or that was just a shop BS ?
fourmat
Explorer
Feb 17, 2016
wildmanbaker wrote:
Corkey05 wrote:
Your F53 has a hydroboost pump to assist braking. It doesn't have a vacuum system.

The hydroboost should work full time so you'll still have brakes if you should ever lose power (or ignition power fails). The idea is for you to have full braking power to stop no matter what.

Your probably hearing the boost pump running, as it will even under light peddle pressure.

Right on the button. This will concern new owners of ford chassis MH until they find out what it is and how it is designed to work.
Ya but that sound is not a hiss its more like a growl
wildmanbaker
Explorer
Feb 17, 2016
Corkey05 wrote:
Your F53 has a hydroboost pump to assist braking. It doesn't have a vacuum system.

The hydroboost should work full time so you'll still have brakes if you should ever lose power (or ignition power fails). The idea is for you to have full braking power to stop no matter what.

Your probably hearing the boost pump running, as it will even under light peddle pressure.

Right on the button. This will concern new owners of ford chassis MH until they find out what it is and how it is designed to work.
Corkey05
Explorer
Feb 17, 2016
Your F53 has a hydroboost pump to assist braking. It doesn't have a vacuum system.

The hydroboost should work full time so you'll still have brakes if you should ever lose power (or ignition power fails). The idea is for you to have full braking power to stop no matter what.

Your probably hearing the boost pump running, as it will even under light peddle pressure.