Motorcycle Repair: rear wheel lock up why?

Question
What would make the rear wheel lock up....riding at 30 mph ,never touched the BRAKES,TRAVELED 100YARDS,..SKIDDED to a stop, NO BRAKE FLUID FRONT,,2t,,ENGINE OIL AND TRANNY OIL FULL,,FILLED BRAKE FLUID..2MINUTES BIKE NEUTAL START 5 KIICKS, ...WENT 100 YDS LOCKED UP AGAIN.....DROVE 5 BLOCKS LOCKED UP...TURNED IT OFF QUICK...HAD TOP END REBUILT 2 MONTHS AGO,,,SAME PROBLEM.....BRAKE PADS ARE 50% AND NO WHEEL OR ENGINE  NOISE.....ANY IDEAS,,THANK YOU FOR UR TIME.....

Answer
Cash, it would have been helpful to know what kind of engine/motorcycle you are riding and if the bike is chain drive, shaft drive or belt drive. Too many possibilities without more information. It sounds like the engine is seizing up, as my first guess. Even 4 cycle engines can seize if the oil pump fails to pump oil to the piston/top end or it overheats due to lean mixture or incorrect ignition timing. If you have to wait a few minutes for the engine to loosen and start up again, then the piston is seizing, most likely. If the chassis or transmission was at fault the engine would start up immediately.

If the piston is seizing, you should see some evidence on the spark plug... bits of metal or now more oil due to piston ring damage and cylinder bore damage. If the spark plug looks clean and the engine has correct compression with no signs of engine smoke out the muffler or breather tube system, then the next thing would be either something to do with the starter engagement system or the transmission has something broken inside. Drain the engine/transmission oil and look for burnt oil odors or pieces of metal in the oil.

The other thing that can grab a wheel is the brakes locking up. Hydraulic brakes can seize up from the caliper piston becoming stuck in the caliper due to contamination of the brake fluid causing the sealing ring to swell up and hold the caliper piston in place against the brake pads. This causes the pads to overheat and seize the brake rotor.

On the back, if it is a drum brake, a broken return spring inside the brakes can jam the brake shoes against the brake drum.

Bill Silver