Yesterday, I experienced the following problem with my son's SunL KLB110 rear disc brake: After riding the bike for about 20 minutes or so the rear disc brake would lock-up. After letting the bike sit for about 5-10 minutes, everything seemed to be okay. Then after riding it again for about 15-20 minutes the rear disc brake would lock-up again. This was confirmed by lifting the rear of the bike off the ground with the trans in neutral and the rear tires would not spin freely. I also noticed alot of brake dust around the caliper. I know my son is not riding with his foot on the brake. Does this have anything to do with heat buildup in the brake system. I noticed that the brake fluid container is right next to the exhaust. Anybody have this problem or have any advise???? I have adjusted the foot brake after we got home because the pedal did not have much play in it and it seemed to tight. Just really wondering if this problem is realated to heat? Would the caliper piston not function/lockup due to excessive heat? The caliper was hot after we stopped the bike. Thanks for any advise.

 

Sounds like it could be heat related because fluid expands when hot. If you can move the container or maybe put aluminum foil around where the most heat is to see if it helps.

 

Try removing the caliper and checking for the remnants of some packaging material. Could be the dealer forgot to take out the plastic transport blocks that some of the minis ship with. May have to beat or chisel out the melted plastic, then should be fine.