brake chamber leaking from rear when brakes applied

It's a failed or unseated diaphragm. I carry a spare diaphragm just for this reason (they are pretty cheap), as this has happened to me also.

To fix it, you have to open up the can, which means removing the ring clamp and separating the "end" piece. There are two ways you can do this... You SHOULD cage the spring, but if you are hardcore, you can simply make sure the can is charged up with air. Do NOT put your face ANYWHERE near the end of the can, no matter what method you use.

Unbolt the ring clamp, slip a new diaphragm in there, make sure it is seated properly, and securely tighten the ring clamp back around the can.

I would really suggest getting a mechanic to do this, as I can not be held liable if you hurt yourself, but it is not uncommon for diaphragms to go, and they are actually cheap and easy to replace, relatively speaking.

 

The spring will be compressed, whether you do it the hardcore way (by ENSURING adequate pressure is fed to the can, but more safely my manually caging the spring)...

Then the can can be pulled apart, and the diaphragm replaced. I guarantee you that is the problem.

A blown or unseated diaphragm will blow out half the tanks PSI in a few brake applications, and is definitely not really something you should drive around with.

 

Those springs improperly caged can hurt you... thats all you need to know in my opinion. Why chance getting put in the hospital or worse just to save a few minutes, but as the driver @fuller said, do it at your own risk.

 

Yea, but for anyone else DIY, safety issues need to be explicitly suggested.