I left work in the early hours of this morning, fired up the MINI, and released the handbrake. As I went to pull off, there was a "thunk" from the back end as though the handbrake had not released, and the movement of the wheel had to break the grip of the pads on the rotor. About half way on a 56 mile commute, I stopped for gas. Applied the handbrake while filling up, and had no "thunk" this time. Just about to go the garage, and see if it happens again. The car had been sitting for about 10 hours. Not freezing cold, raining constantly during my time at work. Car is a 2006 R50. I've not noticed any drag on the car when accelerating, or any loss of braking. Still stops on a dime. Given that I still have good brake function, and it only happens when the car has been standing, this would suggest that something is not releasing when I take off the handbrake? Thoughts, anyone? Okay, just reversed the MINI out of the garage, and same "thunk". Sounds like it is coming from the passenger side. Usual surface rust on rotor after sitting for about 8 hours.
Those cables frequently rust over time. If you disconnect each cable at the caliper end, you should be able to push and pull it through the housing easily with your fingers. If it feels very rough or you can't move it with your fingers, it's probably rusted. New cables are the fix, if that's the case.
do the rotors get warm over time (even when not braking hard)? When calipers drag, things get quite hot - I had that happen with an older car and the entire rim was hot after a 20 mile drive. If there is no drag, they should be as cool or colder than the front wheels when you stop.
The thunk was probably the rotors releasing from the pads. You mentioned that it was raining: the rotors will corrode very quickly in wet conditions and stick to the pads until the car moves. You can check to see if the calipers or cables are faulty by putting the rear of the car in the air and removing the rear wheels. Take a pair of pliers and grab the ebrake levers (that have the cable ends in the bracket) and twisting them as if the cable were pulling them. If the levers move freely (they are sprung, so it'll take some effort) they're probably ok. Then have an assistant pull the ebrake and observe whether both cables pull the levers. If they both move freely, your cables are ok. If one cable is bad, replace both, or you'll end up doing the job twice.
Eric, Thanks for the info. Will try that at the weekend (I'm not working this weekend). Brakes have not made the "thunk" noise recently, as we have had no rain for a couple of days. Would the brand/composition of brake pad used make a difference?
Update. Did not have time to do Eric's procedure this weekend (had to work anyway), but I should be off work at least on Easter Sunday. I've not noticed the "thunk" sound of the rear brake pads releasing from the rotors after getting wet, no rain for a few days. However, I did spray off the MINI at the local car wash on the way home from work last night/early morning. Lo and behold, I heard the familiar "thunk" when reversing out of the garage this morning. I don't have much time in a morning to check things out (I work second shift, and have Cardiac Rehab 3 mornings a week), so I'm hoping to do a full check this coming weekend.
Finally got a bloody weekend off!!!!! Justa in time for the good weather. Tried Eric's procedure, and the cables seem to be working just fine. Going to replace the cables anyhoo. Car is 10 years old, and winters in NW Ohio aren't too kind to anything underneath a car.