I have no experience in this area but I would have thought that O-ring was just to keep the dust out and fluid leaks in.

Any vacuum in that area would suck any leaking fluid into the power booster.

I suspect the bushing that the vacuum line from the manifold plugs into was missing or faulty.

 

At the dealer when they pulled out the vacuum line off of the booster and plugged it with their thumb the hissing sound stopped so the leak was not on the line but was on the master cylinder/booster unit, the garden hose test that someone told me to try earlier in these posts, is a great tool to pinpoint the leak, I could certainly hear the hissing noise right around the O-ring area where the master cylinder sat on booster, I think the ORING keeps the vacuum up and also makes sure the booster stays clean of fluid or debris.

 

That just proves my point. If you plug an area and the hissing stops then that is the place where the leak is to be found.

 

Thanks for the low down, I have a mushy brake problem after storage, I figure the seal is still there as I have not had it apart any other thoughts.I have a case of o-rings one might fit. is it easy to pull apart.

Randy

 

Brakes do not use O-rings, O-rings are not reliable for this application.
There are special brake seals designed for this dynamic application.
Remember lives depend on these seals, so only the most suitable design are used.

 

Thanks for the quick response I was looking at the drawing and it says o ring, safety is paramount and they are not the most expensive part. Have you ever done any work on the issue of bas esp light coming on. The brakes have always seemed a bit mushy.

 

Sorry, I now see where you are talking about an O-ring.
please fully explain your problem.

 

The O-ring in my case was the o-ring behind the booster and it was just to hold the vacuum! There is an easy way to test and see if around that ring air is leaking, A) start the car, B) cut a 3 foot garden hose place one end against your ear and use the other end around the booster where the fluid reservoir is bolted to the booster and see if the hissing increases?
You can move the hose around and listen to all the connecting points for vacuum hoses, you will hear the hiss get louder if there are any leaks. I have attached the picture to this post and the o-ring in my case was #5

My original issue was due to bad master cylinder but when the Chrysler tech replaced it he forgot to use the o-ring, and that caused me to lose my power brakes, so once I got that repaired the power brakes worked fine.