I recently bought a Falcon Cyclone mountain bike from a popular auction website, just something to go out with my 9 year old son and it was pretty cheap for the spec'.
Anyway, we went out the other day and the front wheel jammed up, I ended up wheeling it home on the back wheel. I took the wheel off and found that the part the disc (rotor?) is mounted on, had unscrewed up to the point where it met the forks and jammed the wheel.
After screwing it back in tightly I noticed that the way the thread goes is such that when the brake is applied, it stops the rotor, but the wheel then effectively unscrews it again, which to my mind is wrong, but I've not had disc brakes before. Surely the thread should be in the direction where braking would tighten the rotor mounting, wouldn't it? or does it just need to be tightened up to a particular torque?
Just thought I'd update this thread as I've fixed the problem now. Basically it was due to whoever built the bike up, they'd put the forks on the wrong way around! I simply loosened the handle bar, turned the forks around 180 degrees and tightened the handle bar back up, all sorted.
You never know, someone else may have the same issue, there's a lot of incompetent people out there :-)