Master cylinder

[Vogelstein]

1985 truck.
Did the brake upgrade kept the original booster and just installed a 1" MC today. Bled the system and everything seems good.
Question is when my wife Lets off the brake pedal after holding it I hear a hiss type noise like air is sucking or escaping from the MC area.
What could this be? Is this normal? This is my first Toyota. Thanks.

 

[pappy]

Booster. It has a vacuum line that might be leaking.

 

[KLF]

Is the noise occurring only while the engine is running?

 

[Vogelstein]

This noise is occurring when the engine is off. Have not tried it with engine running as of yet.

 

[ferg]

Engine off seems like a normal operation. There is no more vacuum from the engine and one side of the diaphragm still has to 'breathe'. You do not normally hear this while the engine is running.

Do the brakes work correctly? If so, no worries.

 

[txlonghorn]

Any reason you're not matching the booster to the new MC? Gives a better feel.