So my 6' foot husband drives a 2013 Beetle. Yeah, laugh, but it's been a great lil car with 30+ mpg. At least until now. We put new pads and rotors on, and it needed both rear calipers. All working fine but pedal was sinking mildly so we had a master cylinder installed (that was in Sept). We drove somewhere a couple weeks ago and it was 'acting funny ' and he said the trans had been slipping a little for a while. We decided to sell it at a local lot, the guy test drives it and comes back with all 4 wheels burning hot with the brakes locked up. We had our mechanic look at it, he drove it all over with no probs until it happened to him, but he isn't sure what the problem is. Then my husband drove it about 35 mile trip no prob. I finally drive it the next day, hit the brakes hard and they lock up and won't release, had to force it back home (just went down our road and back). Once it sits for a while they finally release. It seems to happen randomly after pressing the brakes. I'm assuming what felt like trans slipping was brakes sticking. No codes, no brake warning light or abs light. I did not jack it up to see for sure if all 4 wheels are affected but they all seem to get equally hot. Fluid is clean, level is good. Check valve to booster works properly. Booster passes tests (foot on pedal start engine it sinks a bit, foot on pedal turn off car it stays in place etc). Could this be a master cylinder issue? I'm wondering if the place that installed it screwed something up or it was just a bad one. They did forget to plug in the brake light switch which in this car is attached to the m.c., luckily we figured that out. When this happens the brake pedal is hard, the brake lights are on (taillights), and you can shift out of park because the brakes are applied even tho you aren't on the pedal. It feels like a mechanical issue to me, like maybe piston in m.c. isn't returning, but our guy thought it could be the abs system. That seems unlikely? We can't get it anywhere naturally, since there's no way to know when this might happen. So we figure we'll start tearing stuff down. Anyone have an idea where to start? You all are so great and helpful I had to ask here. Thank you and sorry for the book.