You ask we answer. Here's the latest in our "Ask A Mechanic" series.
Q. I've had my dirt bike for several years and kept up on all maintenance. I've noticed the brakes no longer work as effectively as they did when the bike was new. The brake power is just not there. I have bled them to no avail. Is this just normal wear and tear?
A. I would say it's more wear and tear related, but there could be a small amount of moisture in the brake system causing the spongy feel as well.
My first step would be to inspect the entire brake system including the line, caliper, and master cylinder. If no obvious issues present I would clean the pistons on the brake caliper and add new pads and pin. Pins and pads usually don't sell together so for new pins I typically recommend OEM but All Balls and Moose offer some solid aftermarket versions. If that doesn't improve the feel I would then add a steel braided brake line. A steel braided line is stiffer so it's less flexible. The reduced flex increases stopping power and reduces brake fade. If that fails, then I would rebuild the master cylinder and caliper.
Also, it could be the quality of the brake fluid that is being used. I recommend a high quality brake fluid like Maxima Racing Brake Fluid.
Lastly, try changing the type of brake pads. This article should help: Best Brake Pad Material for Dirt Bikes.