I'm looking for some advice here please. A couple of months ago, every now and then, my rear wheel would lock when I shift down into first gear (even had a fall once when it happened in a turn). The problem seems to get worse since lately, when I put it into first from neutral (like at a traffic light), the rear wheel feels like it has the break on. When I pull away, it suddenly snaps into gear and jerks almost into a wheelie sometimes. Would the problem be at the clutch or the gears? Only the first gear that gives me this problem.