Brakes hissing

[Welshy_Pete]

I've changed the discs, pads, calipers, hand brake cable managed to get everything working fine on 306 hdi.

Now there a hissing sound coming from the brake pedal area. You can drive and it will start hissing but when you press the pedal a bit it goes then either comes back or goes random. The pedal goes a bit spungy I have noticed at the back of brake pedal very light fluid damp over the master cylinder seal.

So its all pointing towards a new brake master cylinder?

[ekjdm14]

If there's fluid leaking then yes, likely the master cylinder but the hissing is probably the servo. It could be caused by the faulty MC but for the time swapping bits I'd be looking toward replacing both at the same time.
You might want to check the vacuum pipe going to the servo just in case too.

[Welshy_Pete]

If there's fluid leaking then yes, likely the master cylinder but the hissing is probably the servo. It could be caused by the faulty MC but for the time swapping bits I'd be looking toward replacing both at the same time.
You might want to check the vacuum pipe going to the servo just in case too.

I just checked and found the pipe was not connected fully to the engine top right corner connection it has a clips in place but it wasn't over the clip and just looked on. I'm not sure how long thats been like that as I've not touched that. So I've put that back in the right place to see if that makes any difference.

[Oldpug]

If there is a "hissing" sound INSIDE the car by the pedals it will be the servo for sure.They are a sealed unit so a replacement is necessary.The noise is loss of vacuum,with the engine idling pump the pedal a few times and I bet the pedal will go rock hard(as you have expelled the vacuum).The pedal will then go down a bit as the vacuum builds up again.
Now then,this fluid by the pedal confuses me?? The brake master cylinder is in the engine bay,if that was leaking it would be impossible for fluid to get near the pedals.
The servo bolts to the bulk head,engine bay side, and is operated by the rod on the brake pedal.There is no fluid in a servo,there is nothing inside it,its just a vacuum tank with seals and a diaphragm.The master cylinder bolts to the servo,in the engine bay, and is operated by a rod FROM the servo. If the master cylinder was leaking you would get a bit of fluid near the two bolt flange on the servo.
The thing is? is the fluid reservoir going down? and are you having to top it up with fluid? If so remove the two nuts holding the master cylinder to the servo.Pull it very gently away from the studs,don`t kink the metal brake pipes,then have a look into the servo by the rod for fluid. If its dry you may have a leak elsewhere? check all four corners of the car and the brake compensater valve (if it has one?)

[Welshy_Pete]

What problems does the one way Vacum valve solenoid cause?

Also how do you test this part?

[Oldpug]

That`s nothing to do with the braking system,the main one is on the turbo. If they go faulty you would have an engine problem,engine management light on,fault codes stored etc. I suppose if you tried to drive with a massive vacuum leak the servo would not work,you would have a hard pedal and have to stand on the brakes to stop ??.
All you have on your 306 is a simple mechanical vacuum pump driven by the camshaft,a plastic pipe connecting it to the servo with a simple non electrical non return valve that pushes into the servo.

[Welshy_Pete]

There a brake vacuum pump

https://www.ebay.co.uk/sch/Peugeot-306- ... 660/i.html