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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

Reply to
Volvouser
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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

Reply to
Randy G.

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

Reply to
Robert Dietz

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

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Reply to
Volvouser

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

Reply to
CD

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

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Reply to
Volvouser

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

Reply to
Randy G.

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