Brake booster leak?

A asked this question on the Brickboard but didn't get any replies so here
goes...

Last day I noticed that there was a hissing sound right after I shut down
the engine. Opened the bonnet and noticed that it came from the brake
booster.

After some tracking, I found out that there was a leak at one of the nuts
that holds the main cylinder to the booster. The leak was due to the nut
holding one vacuum hose clamp allowing air to pass the threads.

I placed one rubber gasket in between and that made the hiss disappear from
the nut. Instead there is a much more subtle hiss that I haven't been able
to trace.

The brakes work nicely and it is possible to lock the wheels on asphalt,
however if I brake and shut down the engine, I could feel the pedal press
against my foot.

Do I have a leaky booster? I have listened below the steering wheel and it
is quiet.

TIA

 

If you don't have a mechanic's stethoscope, a meter-long piece of
rubber hose in the ear can be used to trace such sounds.
__ __
Randy & \ \/ /alerie's
\__/olvo
'93 960 Estate

 

The diaphragm in the booster is sealed so that no vacuum can escape from
the central attachment for the master cylinder. If vacuum is escaping
from there then the booster is defective. Alternatively the check valve
where the hose from the manifold connects to the booster may be faulty.
Try pinching the hose shut with the motor running, shut off the motor
and listen for the noise. With the supply hose shut off there should be
no leakage. If in this circumstance the brake pedal still rises after
motor shut off then the problem is indeed internal to the booster.

Bob

 

Thanks, I will try that when the rain stops pouring down!

 

What year/model do you have?
I have a 2001 S60. I too had similar problems. I took it to the shop that
I bought it from and they indicated that brake boosters were a common
problem on these cars.

Charlie

 

Oupps, forgot to inform about that!
It's a 745 from 1988, ie far from a new car.

 

There are actually special clamps sold to mechanics to pinch off hoses
without damaging them. I have a pair of Vise Grip locking needle nose
pliers. I cut two lengths of hose (about 1/4 to 3/8" ID) and slip them
over the two jaws. This gives a soft jaw and smooth radius to pinch
off vacuum lines.

__ __
Randy & \ \/ /alerie's
\__/olvo
'93 960 Estate