Took the MINI out this morning and went to park it. All of the sudden the pressure on the brakes stiffened (best way to describe it) and the brake wouldn't depress fully. The car braked but barely. Took it for a spin in the parking lot and it did it twice. I couldn't fully brake, the pedal went about half way and stiffened. I know my back drivers side rotor is showing wear. Pads are fine on all 4. It also seems to be "stuttering" when fully braking.

Rotors? Calipers? Vacuum hose? I'm looking online and have seen a myriad of possible issues. Just wondering if anyone has experienced this and what to check for?

 

I'm thinking there is a possible vacuum issue here. I do know that signs of a faulty vacuum pump are things such as low brake booster vacuum, hard brake pedal, and brake fade during application when stopped.

 

Did you check the brake fluid level in the reservoir? Are any of your pads worn down to the metal backing plate? You can peek at the outer pads at least with a flashlight looking through the wheel spokes. Just takes a few seconds per wheel. I don't know what your specific symptoms mean though...

Edit: Just noticed you did check pads...