The brakes on standard scoots are decent at best. They work by expanding curved pads against the inside of the wheel drum to slow the wheel itself. While the system works well it can get a little inadequate when you are trying to stop a tuned bike from 80 MPH. The shortfalls of this system can be:

• Hubs becoming oval - This can be caused by excessive heat or by hitting something hard with the wheel and results in the brakes grabbing more in some areas of a complete wheel revolution.
• Oil leaks - This can happen around the rear oil seal and allow oil to lubricate your brake linings which is exactly where you don't want the oil!.
• Snapping cables - If they snap right when you need them it can be ugly.

The best solution is to go hydraulic but it requires a load of parts and some engineering knowledge. I'll try to show what I have learned on a couple of projects.