Vacuum leak after engine shut down

[pugmax]

Hi, My 406 HDI 2.0 has vacuum leak after engine shut down. I can here that hissing noise from turbo solenoid after engine-off for 3-5 minutes due to vacuum from the hose which is connected to brake master. I have highlighted the hose in below diagram which is connected to turbo solenoid valve. actually hissing coming from the solenoid valve, when disconnecting that hose from solenoid, hissing disappears and when keeping my finger on hose end I can feel the vacuum. what is the reason for this? is this normal this kind of vacuum after engine shut down for few minutes? Also this vacuum stopped when I press the brake pedal few times.

[8Jb9]

Sounds like the check valve in your brake booster is faulty. On some it is possible to replace the check valve itself, on others you may have to replace the entire brae booster. I don't know what is the case for the 406.

Under normal operation the brake booster is filled with vacuum on both sides of a membrane. When you step on the pedal you're filling one side with air, which assists your push on the hydraulic piston. When you then let go again the vacuum that is left on the other side is shared with the side you vented when you pushed the pedal to let you remove the pressure on the brakes. After a couple of brake-taps the brake-booster has normal pressure on both sides.

[pugmax]

Sounds like the check valve in your brake booster is faulty. On some it is possible to replace the check valve itself, on others you may have to replace the entire brae booster. I don't know what is the case for the 406.

Under normal operation the brake booster is filled with vacuum on both sides of a membrane. When you step on the pedal you're filling one side with air, which assists your push on the hydraulic piston. When you then let go again the vacuum that is left on the other side is shared with the side you vented when you pushed the pedal to let you remove the pressure on the brakes. After a couple of brake-taps the brake-booster has normal pressure on both sides.

Thanks for the reply. I will check the check valve in brake booster.

[GingerMagic]

My turbo solenoid used to hiss sometimes, or vibrate, couldn't really tell. Only after switch off - I assumed it was normal.
The servo should hold vacuum, when I stripped my old 406, I never removed the vacuum to the servo - didn't need to - but when I did after the car was nearly all gone, there was a whoosh of air as I pulled the pipe off....