Hey demon, thanks for the reply, I'm hoping to troubleshoot this ahead of time so I can order any parts etc and give them specific instructions because I've already had it into this shop 3 times for the brakes and I'm getting fed up with it.

I do hear a hissing of sorts (like the sound of air leaking from a tire) when the engine is running coming from where the vacuum hose attaches to the booster (see photo I attached). If I put my finger over that little nipple you can feel the suction like when you put your hand over the end of a vacuum cleaner hose. That's not what you mean is it?

Also to answer you other question, it has discs in the front and drums in the rear. I don't think they adjusted anything on the brakes themselves when they replaced the master cylinder. And it does brake fine, you just really have to come on to it hard to make it stop.

 

Seems like you have a vacuum leak there. Plug that hole with a vacuum cap and your brake assist should return to normal. That line should be sealed, shouldn't hear any hissing.

 

Wow amazing that such a small thing could be causing that problem! I jury rigged it a wire screw on connector and a little duct tape and 'presto' suddenly I have power brakes again! Thanks a bundle man, you saved me a lot of hassle and probably money. Looks they sell kits of those caps on amazon with various sizes so I'll get one of those and do the job right, thanks again!

 

If you have an auto transmission, there should be a vacuum hose from that nipple to the transmission The transmission pressure is vacuum controlled from this line. With a manual transmission there should be a cap on that nipple.