I was just driving down the street and my rear brake locked on the passenger side. There was a loud popping sound from that side then the tires could be heard squealing which halted my car. I am pretty sure that it was just the tire on the passenger side. I know that that the brake caliper leaks on that side but my mechanic said it was minimal enough to ignore for a bit. I check my brake fluid regularly and it was full when this happened. After I checked everything and couldn't see anything obvious, I started my car and the brake released allowing me to drive home. Not sure what it is but I am not going to risk anything.

A little background info the car is a 1998 Mazda Protege with a manual transmission. The car has 210,000 miles on it. It sat for about 4 years before I got it last year. The driver side brake was locked when I got it but I had that fixed and I haven't had any problems with the brakes (except for the leaking caliper) ever since. I want to drive to my parents house tomorrow 170 miles away but I am not going to bother until I have this thing fixed. Also side note, When this occurred, the weather was about 45 degrees and raining so the brakes are wet. Any help would be awesome.