A couple of gremlins

Took off a pipe that runs along the front of the engine from just under the throttle housing and goes along to the accumulater down the n/s/f. The pipe seemed to have a small nick in it where I think it's been rubbing. I sealed it up with a few wraps of duck tape and checked the rubber pipes and hose clips. All is ok but still the hard pedal. Tomorrow I'm going to take the other pipe off that goes from the accumulator to the master cylinder in the hope that I'll find something conclusive there.

Getting really fed up now

Right, finally the end of one conundrum <spelling?)  I am now very sure what the hissing noise is and why it's only just started. The pipe my mechanic thought went along with the dash wiring and under the carpet is a red herring!  There is a pipe and it does run behind the glovebox but it goes behind a metal plate then seems to come out the other side (as my mechanic thought) but with my bony little fingers, I managed to feel along the pipe and realised it turns downwards at 90 degrees then swells into a rubber dome about 1 inch across. The 'pipe' coming out the other side is actually electrical sheathing for some wires which also run along the same route as the pipe but nothing to do with it in any shape or form.

So back to the rubber dome, this sits directly above an opening which comes out behind the glovebox. The opening is making a hissing noise which when I cover it stops!  if I remember correctly, it's something to do with the climate control and measures the air temp in the car?

The pipe that BPB mentions is blanked off on his car (lack of climate control?), on my car it's one of the old perished pipes that I replaced and it goes into the bulkhead directly behind the glovebox! I therefore assume that there is a unit which uses the vacuum to suck in air so that it can measure the temperature to allow it to control the temp inside the car.

It's just started hissing because it was obviously not working at all before due to lack of vacuum but I'm now wondering if the pipe I took off which had something stuck in it was acting as a restriction or muffler and so wasn't so loud?

Now with that sorted and knowing my brakes are not linked to the hissing I can turn my full attention to the brakes. Now as you mention it BPB, the pipe I  described does have a little sort of valve unit on the end of it. I'll have a look on realoem and see if I can spot it to cast more theories in to the mix.

Together, we'll get to the bottom of this.

Mike

Mike,
I think you need to take a picture of what is on your car so we have somewhere to start, because it sounds as if it might be unusual.

My car has full climate control.

I think the dome you refer to is just the back side of the large grommet to seal the firewall where the cables go through.
I had a feeling that there was something that sucked a bit of air for climate-control purposes, and thought I had mentioned it before, butmaybe not.
The non-climate heater-control panels have a little fan that blows over the temperature sensor behind the temperature knob, so it is all internal.

When I fixed my manifold leak there seemed to be a new hissing noise from somewhere but in my case it seemed to be down by by the clutch pedal somewhere. I worried for a bit and then it seemed to go (It was only very slight).

The 530iT does not have any of the extra vacuum system gubbins that realoem shows it to, so that is a realoem red-herring in this case.

The pictures you have uploaded are of the hydraulic accumulator and plumbing for the brake/steering hydraulics.
I wouldn't advise you start breaking more connections, and also think they will be unrelated.

The part I am talking about is the evaporative emissions canister and plumbing. It has a mixture of rigid and flexible pipes so scope for cracks and elaks and the solenoid can stick.
You can find it in .....=>Fuel supply=>Vent

Is the engine running smoothly now, or is there still an symptom other than the hissing noise?

Good luck!

I think all the brake stuff is purely hydraulic, so none of that would cause your hissing.

bpb, what does the full-climate-control panel look like?  I thought the systems were basically the same behind the panel.  Mine has the three knobs and three sliders and I think it has a fan for the temp sensor.

Mike, If you don't have aircon, I think the temperature sensor has air drawn over it by a vacuum line rather than a fan, so that might be worth checking.

I have shown the vacuum pipe I have been on about all this time! You can see it coming from the PCV valve and it loops under a water pipe then into a grommet in the bulkhead. (PIC 1)

In the second picture you can see the other side of where the pipe comes through, into a plastic tubular housing where two vacuum pipes come out, one goes off to the drivers side and the other is shown in the third picture as routing along to the dome shaped rubber (hidden but outlined in red in pic 4) then you can see the opening where the pipe sucks from.