Hissing noise from brake pedal area

[harvey94]

Hi,

I have asked about this before but thought i would ask this in the proper section this time. Basically after having a noise after getting a bush replaced i had my radio and air blower off to listen for the noise , i then noticed that there was a hissing noise coming from my brake pedal area , if i gently press the brake and let go then i constantly hear a hissing noise , if i put my foot under the pedal and lift then its stops. I did take this to the garage and they test drove it and said don't worry its fine but what i noticed is that he pumped the pedal when first getting into the car which makes the noise stop for a bit.
From what i described the mechanic was not concerned and said that all i was hearing was the vacuum noise.

Has anyone else ever heard this and is this something i can just ignore as my brakes have been checked and they are fine?

thanks

[James burbidge]

Dontno really sounds weird doe. Hmm duno how the pedals are mounted or fixed but what makes the pedal Spring back up could be to do with that.
Good luck with that
Be sure to let us know what it is if you ever find out

[mab01uk]

As the mechanic said it is likely to be vacumn noise coming from the brake servo, keep a check on it in case it becomes excessive or is an air leak, if you lost all vacumn the brakes would still work but be very heavy to apply, as the vacumn/servo gives power assistance to the brakes reducing the pressure required by the driver on the pedal.
Like power steering many older cars did not have brake servos and therefore had much heavier braking effort required from the driver on the brake pedal!

[harvey94]

Thanks, it's a strange one, 100% no difference in my brake pedal , it's as if the Pedal is not lifting high enough sometimes as when I put my foot under it and lift the noise stops. Will just keep an eye on it.

[mab01uk]

Perhaps there is a return spring on the foot pedal that has weakened or is sticking or it may be internal to the servo/master cylinder itself. The hissing may be vacumn/air leaking away when the pedal has not fully returned to the up position, but as long as the engine is running it quickly gets replenished for the vacumn reservoir to power the servo.
Not 100% sure on the Mini pedal return set-up as not seen this problem before......might be worth looking at the parts diagrams on Realoem.com to see whats what......unless you get other replies here that help.

Also check the pedal returns enough (when hissing) to switch off your brake lights. as this is usually done via a pedal position switch/sensor.

[harvey94]

Thanks , didn't think about my brake light , will check that out , had a look at the pedal last night although this was not easy at all lying on the floor upside down with me being 6ft 3 , i just gave it a spray and left it over night so will see what happens.

Just out of interest , if it turns out to be the servo , is this a big job to replace? if its an expensive task then i may be aswell putting some cash away just incase

[harvey94]

Found this.....

www.bmminiparts.com - Diagram View

i can see a spring , could this possibly be my problem?

[mab01uk]

Looks like that is the pedal return spring, check it out with your mechanic to confirm and if it has weakened slightly that should be cheap and easy to replace, so worth a try.....unless your spray works.

[harvey94]

Well I took her for a wee drive tonight and the problem is still there, noticed that when switching off the engine I hear it for about 15 seconds after , one of my friends said I should get it fixed if it's a servo leak as in time breaking will become harder and he also said that it won't be great for full economy and can be a cause of not idling good?

Well don't know if any of that is true or not? I just know I have this noise.

Well is anyone able to tell me if it is in fact the servo what a rough cost is? Or even just how long the job should take so I can work out a labour cost.

If it is the servo and there is no harm in just leaving it to wait and see then I will but not if the above is true on the likes of fuel economy and idle.

[mab01uk]

What you need to find out is if and where there is an air leak......could be in the servo itself (there is a diaphragm inside) or in a hose or valve, tracing the source of the hissing noise exactly should give a clue. As the vacumn required is created by the engine usually via a hose any air leaks can cause erratic idle or loss of braking assistance.

The brakes would still work the same but need much more foot pressure but it can be alarming if it catches you out unawares......as happened to me once a few years back in a brand new Peugeot hire car when a servo vacumn hose split!

Labour cost is similar to replacing a brake master cylinder and bleeding the brakes......servo/master cylinder part prices vary quite widely but remember it may yet be nothing or just a leaking rubber hose.

[harvey94]

Thanks, really appreciate the advice and I know it's hard to judge what's wrong on a forum , I think it's best I just book her in and get a proper diagnoses done, if it was just me driving then I think I would wait and see but as my partner drives her I would never forgive myself if the worst happend, she is only 5ft 4 and there is more meat on a vegetarians plate then on her

Will post back with the outcome

[harvey94]

Well before taking her to the garage this morning I thought I would take her for a drive , I could not get the noise to happen! Drove around some more and parked her up on the drive and left engine running, got down and got as close to the brake pedal as I could , no noise at all, even after pressing pedal a few times softly as before, maybe my white grease has set in and worked? Who knows but for now I will just keep an eye on her as there is no point going to the garage if she is not doing it!