brake chamber leaking from rear when brakes applied

Any air leak at the chamber is a failed chamber or failed service brake diaphragm seal. Crossed lines do not leak, just reversed brake behavior. If you are leaking air out the rear of the chamber you just installed, then the diaphragm, (rubber gasket) must have a split or hole in it somewhere. Getting the chamber, diaphragm and clamp all lined up is tricky. This is one of those jobs you need three hands for! It is easy to have everything lined up, then you look down to grab a wrench, and everything slides out of place when you aren't looking. So it is easy to get it mis-aligned and then leak afterwards.

 

My technical experience suggest replacing the diaphram which is not in new condition.

 

last truck I got was from Mankato Freightliner, they replaced the front part of the chambers, same thing,
in different shop the next day, said they wern"t lined up right before tighting down the ring

 

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adjust your brakes if you havent already .... over extending the diaphragm can tear or unseat it if your brakes are very worn and your sack adjusters are set very loose.