I thought that the headset on my MTB was dead when I did the good old brake test and tried to wiggle the wheels back and forth. However, my dear cyclist hubby tested and he just found out that the headset's fine, it's the wheel that moves. Quite. So the front disc brake obviously doesn't lock the wheel properly? No. The brake locks the disc, yet when wiggling it the wheel moves a tenth of an inch or so back and forth by the rim. However, the movement is not even visible in by the hub. Weird? The brakes are firmly fixed to the fork, the wheel is properly mounted and the bearings in the hub are tight.

There seems to be some sort of adjustment that isn't right, but what adjustment could it be? We're noobs in the disc brake department, and we believe it has something to do with the brakes, mainly because they're the only component that we aren't fully familiar with...

Any ideas?