Hey..

 

Did a front and rear pads change last night. After front drivers side (first set I changed) I dropped jack and pumped the pedal slowly - straight away it hissed.. LOUDLY! It did not do this before.

 

People have been telling me all day that it's normal... I even sat into a 2011 superb in the car park at work this afternoon and the pedal hissed.. Mine never did this before. It's as a result of the pad change. I'm thinking it's related to the winding back of the piston, possibly disturbing a seal or o-ring or something. 

 

Has anyone any ideas? There seems to be a lot of instances of it online.. people argue over whether a bleed will fix (no air should get in or out with a simple pad change, right?), whether the master cylinder has a leak or whether it's just normal.

 

Does anyone know for sure?

Thanks guys..

 

2010 Superb Mk2 1.9 105Bhp Saloon..

You ALWAYS need to bleed the system after changing pads or discs.

5 hours ago, jafo said:

You ALWAYS need to bleed the system after changing pads or discs.

 

Rubbish. If you do, you are doing something very wrong.

 

Back to the OP, are the brakes operating normally with no sponginess?

Whre is the hissing coming from?

Yes the brakes are working as normal with the exception of the "woooossshh" from the pedal where it disappears through the carpet. 

 

The only mechanical change I can envisage doing damage is some possible effect the winding back of the piston has on the fluid system? As in it pops a seal somewhere?

 

The pedal isn't spongy and returns as normal.

 

Where is the air coming from and what is the problem? !

Check the brake servo vacuum hose for splits/cracks.

Where is this, just the other side of the firewall from the pedal? Thanks..

When you retract the piston you're supposed to clamp the pipe and release the bleed nipple for the excess fluid to come out of otherwise you risk flipping the seals in the master cylinder. I must admit it is rare that I do this myself as retract the pistons slowly so little chance of pushing enough fluid back to cause a seal to flip. 

As others have said check for leaks and cracks, follow the pipes down from the master cylinder and check for leaks as some cars a combination of hard and flexible pipes that run along the body and finally the flexible pipes that connect to the caliper. 

 

Thanks.. I'll try that this evening.. how much is a new master cylinder does anyone  know?

Checked hoses thoroughly - no cracks or leaks visible. Bled the system too.. still wooshing. 

 

I'm reluctant to accept that it's normal.. given its the breaks!

 

Any further advice out there? 

 

Thanks..

On 8/10/2017 at 09:34, CWARD said:

When you retract the piston you're supposed to clamp the pipe and release the bleed nipple for the excess fluid to come out of otherwise you risk flipping the seals in the master cylinder. I must admit it is rare that I do this myself as retract the pistons slowly so little chance of pushing enough fluid back to cause a seal to flip. 

As others have said check for leaks and cracks, follow the pipes down from the master cylinder and check for leaks as some cars a combination of hard and flexible pipes that run along the body and finally the flexible pipes that connect to the caliper. 

 

If pushing fluid back to the piston could cause the seal to flip you'd have big problems, there is no difference in pushing fluid at the piston and pushing the piston at the fluid (normal braking).  The only reason to release fluid from the bleeder when pushing the pistons back is to prevent the returned fluid filling the reservoir and overflowing.  Best to suck most of the fluid from the res' first.

On 8/10/2017 at 07:09, BJM said:

 

Rubbish. If you do, you are doing something very wrong.

 

Agreed.

8 minutes ago, Gdcobra said:

The only reason to release fluid from the bleeder when pushing the pistons back is to prevent the returned fluid filling the reservoir and overflowing.

A better reason for opening the bleed valve is that the brake fluid that you would otherwise be pushing back up the pipe towards the ABS module is going to be the most degraded, thermally 'challenged' and dirty (from seal detritus) fluid in the whole system, and bleeding alone is less likely to remove it than doing so by pushing the piston back in with the bleed valve open.

 

Your analysis of seal flipping/not sounds spot on though.

1 hour ago, Gdcobra said:

If pushing fluid back to the piston could cause the seal to flip you'd have big problems, there is no difference in pushing fluid at the piston and pushing the piston at the fluid (normal braking).  The only reason to release fluid from the bleeder when pushing the pistons back is to prevent the returned fluid filling the reservoir and overflowing.  Best to suck most of the fluid from the res' first.

 

Retracting a piston when you have had worn pads moves a lot more fluid than releasing the brake pedal where the piston remains extended.  Next time you change pads see how the fluid is lower in the reservoir and then refills when you push the pistons back.  

On 8/11/2017 at 20:11, CWARD said:

..  Next time you change pads see how the fluid is lower in the reservoir and then refills when you push the pistons back.  

 

Wow!  Who knew?  I thought the returned fluid just disappeared into the ether.

 

Seriously though, of course you have a higher volume of fluid moving but at very low pressure against a seal which is designed to act in this direction.  I've never "flipped a seal" or heard of anyone who has and knowing what goes on inside the mastercylinder can't see how this can happen.  Not pushing contaminated fluid back into the ABS gubbins is a good reason to release the excess fluid at the wheel cylinder, but not for seals.

 

 

I was a bit intrigued by this mention of hissing, I've never heard it,  so when I got in my car on Friday evening thought I'd give the pedal a prod or two before I set off.  Guess what?  It hisses.  It's only quite faint, can't really hear it with engine running, certainly not with radio on, but it is there.

there's you're solution then, turn on / up your radio system!  ; - D)

Well you've never heard of flipped seals so it must not exist, pretty much like the OP's hissing sound too. I guess these are all figments of imagination because you've never witnessed them. 

 

Quote from Haynes manual

Quote

"Caution: Pushing back the piston causes a reverse-flow of brake fluid, which has been known to 'flip' the master cylinder rubber seals, resulting in a total loss of braking. To avoid this, clamp the caliper flexible hose and open the bleed screw - as the piston is pushed back, the fluid can be directed into a suitable container using a hose connected to the bleed screw. Close the screw just before the piston is pushed fully back, to ensure ensure no air enters the system."

https://manualzz.com/doc/15536917/haynes-sample-pdf---front-pads

 

Figments of imagination are contagious 

6 hours ago, CWARD said:

Well you've never heard of flipped seals so it must not exist, pretty much like the OP's hissing sound too. I guess these are all figments of imagination because you've never witnessed them. 

 

Quote from Haynes manual

https://manualzz.com/doc/15536917/haynes-sample-pdf---front-pads

 

Figments of imagination are contagious 

Didn't say it can't happen just that in 30 odd years of maintaining and (re)building cars I've never had a problem and knowing what is inside a mastercylinder don't see how this can happen.  If you don't want to do it then don't bother, as has been said it is probably better not to flush old fluid back though an ABS system anyhow.  Can get a bit messy though if you don't have a convenient piece of pipe to fit to your nipple.

On 11/08/2017 at 18:40, Gdcobra said:

If pushing fluid back to the piston could cause the seal to flip you'd have big problems, there is no difference in pushing fluid at the piston and pushing the piston at the fluid (normal braking).

 

A slightly different tune to your earlier statement

2 minutes ago, CWARD said:

 

A slightly different tune to your earlier statement

No it's not.  I don't see any difference, you basically have fluid moving towards a piston rather than a piston moving towards fluid,  if this movement could cause the seal to flip I'd me more worried about it happening when I'm using it to stop the car.  I don't worry about the problem, I don't believe it can happen, I believe even less that it will and I'm not going to change how I service my cars and bikes.  I've known Haynes be wrong more often than I've heard of brake seals flipping.

 

But if it means so much to you to be right then do the job your own way, I won't get offended and you can't possibly have the problem you describe.

 

Having said all that I don't really see how any of this helps someone with a totally unrelated issue so I think I'll make that my last word on the issue.

 Goodbye.

 

@TheDude https://www.yourmechanic.com/services/hissing-noise-when-brake-pedal-is-depressed-inspection

Thanks for all the replies.. much appreciated. 

 

Whatever about it being "normal" to hiss, it's certainly new to me. If anyone sits into a new car I'd be interested to see what happens with the brake pedal before and after cranking. 

 

I wasn't watching where I was going last Friday and ploughed the superb into the side of the boiler enclosure at home..!  Nothing brakes related..

 

Lots of nice paintwork and reshaping of the bumper to follow the new lamp replacement...

 

It's amazing how quickly I forgave myself for it!

 

Not a good month for you. Hope your luck changes soon but for now I wouldn't bother buying any lottery tickets. 

1 hour ago, TheDude said:

Thanks for all the replies.. much appreciated. 

 

Whatever about it being "normal" to hiss, it's certainly new to me. If anyone sits into a new car I'd be interested to see what happens with the brake pedal before and after cranking. 

 

I wasn't watching where I was going last Friday and ploughed the superb into the side of the boiler enclosure at home..!  Nothing brakes related..

 

Lots of nice paintwork and reshaping of the bumper to follow the new lamp replacement...

 

It's amazing how quickly I forgave myself for it!

 

Oh dear, that's not good to hear.  When you say what happens with the brake pedal do you mean in terms of hissing?

I know in mine the pedal is hard until I crank when it softens up and moves downward (have to keep foot on pedal when starting) this is normal for a car with servo.

Would it be worth finding a dealer with one in and go and check it out see if its same as yours?

Maybe your car was 'wrong' before and right now.

 

Edit

Just been out now to check, with engine stopped pedal hisses when pressed for about 3-4 strokes and it also gets harder each stroke (Ooh err)

After about 4 strokes it was quiet and hard, presumably because all residual vacuum depleted.  Maybe this gives a clue what the his is.

Edited 14 August, 20178 yr by Gdcobra