Hissing noise when braking??

[M3_Power]

Okay I've just bled my brake recently - all 4 ... and I've noticed that now whenever I brake and just prior to coming to a full stop I hear this hissing air noise ... it's like "tzzzzzzzz" quick and short ...

Anyone know what it might be??

EDIT: And the noise is quite loud ... Sounds like a leak or something ...

Also when I did the bleeding I didn't release one of the bleed screws enough and I had pumped the pedal quite hard a couple of times before I realised my mistake ... could I have damaged something???

Any help or comments appreciate it.

[tysonzane]

This may sound dumb, but did you fill your brake master cylinder up after you bleed the brakes

[M3_Power]

Yep I did ... I kept topping it up as I was bleeding it.

Also the noise is a little bit intermittent ... it comes and goes ... Occassionally it happens 2 or 3 times consecutively ... occassionally it doesn't happen until the 6th or 10th stop...

[Rumble]

what are the brakes like to use?

normal or harder? ???

[M3_Power]

Originally Posted by Rumble

what are the brakes like to use?

normal or harder? ???

Quite normal ...

[tysonzane]

Originally Posted by M3_Power

Quite normal ...

In theory it should be alot harder/stiffer and more responsive

[Pnut]

Check your pads, when they get low there is a squealer section in the pad or a sheet rivited to the pad to tell you when it is getting low. If the pads are good and it has the rivited sheet you may have bent the sheet into the disc a bit.

If it were leaking it wouldn't hiss, hydraulics works different to air so if a tube burst or nipple leaked their is bugger all noise, just no action happening. Air systems on the other hand will hiss . . . you don't have air brakes do you?

[gazmaster]

Does your car have ABS??

It could be that

[M3_Power]

No car does not have ABS

The pads are brand new and don't squeel.

And I don't have airbrakes

I am thinking whether it could be the brake booster itself leaking??? I was told that the booster operates via vaccuum??? Could I have damaged the booster itself when I bleed my fluid?? Remember I didn't undo the nipple enough and I continued to pump hard on the brake pedal ....

[tysonzane]

how old are these new pads, i.e. how many k's, have they been properly worn in. What are the pads made of??

[Pnut]

they might not squeel, but when you bled the brakes you make have knocked the squeel shim or even some dirt or stone into it.

You could check to see if all the vacuum hoses are connected to the booster and then get someone to hold it at like 1500rpm and pump the brakes so you know its got vacuum and should be able to hear where it is hissing from. If it doesn't do it when it is stationary then i am going with my conclusion above as it is the most common happenings :wink:

[M3_Power]

Originally Posted by tysonzane

how old are these new pads, i.e. how many k's, have they been properly worn in. What are the pads made of??

The pads are Metal Kings ... they are about 500km old ... I used the bed in procedures I got off the internet 8O 8O ...

Originally Posted by Pnut

they might not squeel, but when you bled the brakes you make have knocked the squeel shim or even some dirt or stone into it.

You could check to see if all the vacuum hoses are connected to the booster and then get someone to hold it at like 1500rpm and pump the brakes so you know its got vacuum and should be able to hear where it is hissing from. If it doesn't do it when it is stationary then i am going with my conclusion above as it is the most common happenings :wink:

Okay I'll try that procedure you've recommended. I've been told that it could be due to a rip in the diaphram in the booster or the reservoir cap seal has gone bad?? Would any of these 2 things above cause this sort of hissing noise??

I personally doubt that the noise is from pads squeeling ... The noise is quite obvious like an air suction or release noise ... not metal high pitched squeeling ... It's a bit like the noise that buses make when they stop ... that "hisssssssssss" sound ...

[Pnut]

if it isn't braking any different i doubt it is the booster, the booster amplifies the brake pressure and so if it leaks you will either get wicked brake fad or get stuff all brake pressure.

I could be wrong though, seems to happen regularly according to the missus so let us know how you get on :wink:

[M3_Power]

Originally Posted by Pnut

if it isn't braking any different i doubt it is the booster, the booster amplifies the brake pressure and so if it leaks you will either get wicked brake fad or get stuff all brake pressure.

I could be wrong though, seems to happen regularly according to the missus so let us know how you get on :wink:

Thanks for all the help ... I'll let you know how I get on ...

[NAspirated]

you still have air in the system, caused by one of the following:

1. faulty caliper piston.

2. If you have drums, faulty/seized wheel cylinder

3. you did not bleed them properly. bleed them again. LH rear wheel to RH rear wheel to LH front to RH front. Top up the master cylinder after every wheel. Each wheel should be about 6 pumps on the brake to bleed properly. Push the peadl slowly in anfd release it slowly as well. people push the pedal to quickly which just send the new fluid straight through the caliper without pushing the air out.

4. Highly unlikely but, Worn Pad. I doubt this very much, as you would have heard it before you bled the brakes as well.

your booster wont be leaking, so forget about that idea.

[M3_Power]

Originally Posted by NAspirated

you still have air in the system, caused by one of the following:

1. faulty caliper piston.

2. If you have drums, faulty/seized wheel cylinder

3. you did not bleed them properly. bleed them again. LH rear wheel to RH rear wheel to LH front to RH front. Top up the master cylinder after every wheel. Each wheel should be about 6 pumps on the brake to bleed properly. Push the peadl slowly in anfd release it slowly as well. people push the pedal to quickly which just send the new fluid straight through the caliper without pushing the air out.

4. Highly unlikely but, Worn Pad. I doubt this very much, as you would have heard it before you bled the brakes as well.

your booster wont be leaking, so forget about that idea.

Thanks for all the suggested possibilities above. I'll try and eliminate and see if I can figure out what is causing it.

I think you might be right that I probably didn't bleed the system properly and there's still a lot of air in the system ...


Thanks for all the replies so far ... appreciate it.

[NAspirated]

remember when bleeding a brake system you need to start as far frm the master cylinder as possible and work your way closer.

start at the LH rear wheel, then do the RH Rear, then the LH Front, then the RH front

[Pnut]

I don't get it, why would air in the system cause it to hiss? And if the pedal is still good?

[Chris]

Originally Posted by NAspirated

remember when bleeding a brake system you need to start as far frm the master cylinder as possible and work your way closer.

start at the LH rear wheel, then do the RH Rear, then the LH Front, then the RH front

That method is true for a front/rear split system, but wrong for a diagonally split system i.e. a Honda system.

Take a look in any Honda workshop manual and you will see the order is:
1: Rear Right
2: Front Left
3: Rear Left
4: Front right

1 & 2 are from the primary piston in the MC, and 3 & 4 are from the secondary piston.

Also as Pnut said, if there is air in the brake lines there is no way you would hear any noise, you would only have a soft or spongy pedal.

Any hissing related to the braking system could only be the vacuum booster, if it or the vacuum hose are leaking then it may also be a contributor to your poor fuel economy as in your other post.

here are a couple of ways to check the booster.

1. Press the pedal a few times with the engine off, then hold the pedal down and start the engine, the pedal should go down slightly.

2. Start the engine, let it run for up to a minute, turn it off. Slowy push the brake pedal a few times, the pedal should get higher and firmer after about 3 times.

If it doesn't do what it should then there is a chance that the booster is not airtight.

[NAspirated]

very true, my apologies.

[JJ]

any chance you didnt fully do up the bleed valve thingys on one of the corners?

[M3_Power]

Okay problem solved ... hopefully ....

The master cylinder wasn't tightened up properly - the 2 bolts connecting to the booster was loose.

Also I had a lot of air in my brake lines ... so a nice rebleeding of all 4 corners ...

Now the hissing is gone ... well at least I haven't heard it for a while now ... fingers crossed...

Thanks all for all your comments.