Brake servo problem?

[Lee H]

Went to finally drive the car after its rebuild last night and have a problem with the brakes.

Pedal pumps up fine without the engine running but once its running and I brake I get a hissing noise and the pedal is really spongy. If I keep my foot on the pedal it starts sinking until I pump it back up.

Car is running V6 brakes and a GSi brake servo. All was working fine when I took the car off the road a few years ago.

This going to be a dead servo?

[Will F]

Yep, classic symtoms of a shagged servo are that it pumps when no vacuum (engine off) and loses pedal when engine is started.. either seals have perished or inside out

[craig green]

I replied on MIG.

[Adam]

Maybe worth just checking the vacuum pipe to the servo first.

[burgo]

i had the same problem and it turned out to be the master cylinder seals. i didnt have the hissing noise tho

[Lee H]

Swapped the vacuum pipe with the known working one off my XE to rule that out as that was the easy one!!

Hissing noise is definitely louder than on my other Nova.

[craig green]

Is it a constant hissing with the engine running?