I think this is Drivetrain related?

I hit the brakes hard about a week ago - didn't lockup or skid but stopped really fast for a yellow about to go red at about 35mph - yeah she stops quick for sure. Heard a clunk during that stop and after that the brake pedal was a little lower than usual and sometimes if I kept pressure on it while stopped it would go further down to the floor almost before getting hard and stopping. Yet sometimes it feels normal with light pressure. Fluid is full and clear as the day I bought it and I don't brake much so I may have just freed up a stuck rear shoe? anyway before something bad happens anyone else think that I may have a master cylinder problem starting? 33.9K miles on the odo. 2006 manual tranny original shoes and pads and not much wear on them.

 

Brake booster. You fubared something inside of it.

 

Brakes still seem ok but I have not hit them really hard again - there is a few odd things that happen if I pump them quickly when stopped on an up hill - like the pedal gets a little stiff and slow to move - maybe some vacuum reduction issues in the booster. When the weather cools off a little more and I get into a garage I will pull the rear drums off and check the automatic adjusters to make sure they are moving properly.

 

It is either your brake booster or master cylinder. Either one they need to be looked at.