Brake Booster Hissing

OCCoupe

OCCoupe

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Last Tuesday I decided to tackle what I thought would be a quick repair on my coupe. My steering wheel had a bit of play in it and I was told by a few people that loosening the nut at the top of the steering box and slightly tightening the bolt with a screwdriver would remedy the problem. This was true, I was able to accomplish this. The mistake I made was assuming this would be an easy job. What I thought wold be a 1 hour task turned into a 5 hour challenge. I ended up removing the master cylinder, moving the booster and the power steering reservoir and also removing the coolant expansion tank. After putting everything back together and bleeding the brakes I now can hear a hissing sound from inside the car when depressing the brake pedal. The brakes work well, and once the car has been running for 20 minutes, the hissing pretty much goes away.

Was there a seal or gasket that I missed? Was I supposed to use any type of gasket maker or sealer?

Thanks in advance for the advice!

Mike
 
There is an O-ring that goes between the mater cylinder and the booster, which is very easy to forget. Also, perhaps the vac line going from the intake manifold to the booster isn't clamped tight enough?
 
Thank you X_Atalas0. The vacuum hose going from the manifold to the booster is fine, I checked it and it is tightly clamped and in good shape I will give the O-ring a try next Tuesday.
Mike
 
So you can hear it inside the car? Have you listened outside the car, with someone else pressing the brakes, so you can directly identify the source? I ask because none of the braking components are directly inside the cabin. Actually, the only part that is even conected to that system that is relatively close to the cabin is the clutch master cylinder, which is connected to the braking system. However, you said the noise is connected to braking, rather than clutching, so I would guess that isn't it.

Have you bled the brakes?
 
Also, if a vacuum leak, you may be able to locate the hiss by spraying aerosol penetrant in close proximity to the booster seams and attaching points / around the booster.

Use the hose attachment, stay away from anything hot (exhaust on other side, so you should be okay), and you don't need much vapor. When your idle speeds up, you've found your leak.
 
CookeD said:
Also, if a vacuum leak, you may be able to locate the hiss by spraying aerosol penetrant in close proximity to the booster seams and attaching points / around the booster.
Click to expand...

An alternative to aerosol penetrant is to open the valve on your propane torch while you play its tip around the hose and booster. Again, the engine will speed up when the propane is sucked into the source of the leak. Even on the odd chance that the propane should ignite, you are no worse off than if the torch was intentionally lit.
 
Yes, each will work.

As an aside, and I doubt you'd ever get anything igniting when it comes to using propane for this, but on the off-chance that something weird happens, you don't want flames around the fuel lines and where the lines attach to the inline filter (which happen to run right behind the booster). With aerosols, it's on/off, and small shots.

Be safe, and keep up posted.
 
I was hoping to look for leaks this weekend; but unfortunately the rains have put a damper on my plans to work on my Coupe. Hopefully it will clear up by Sunday, I'll keep everyone posted, thanks for the great advice. Unfortunate, I'm not allowed to play with fire.
Mike
 
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