2002 Ford Explorer RIGHT REAR TIRE LOCKED UP WONT SPIN

If the wheel is locked up at all times then it is probably a fault on the parking brake system.

The vehicle is equipped with a vacuum-assisted power braking system. For additional information, refer to DISC.
An optional adjustable brake pedal (with or without memory), is available on the Explorer and Mountaineer. The driver can adjust the brake pedal and accelerator pedal position using the adjustable pedal switch located on the LH side of the instrument panel. For removal and installation of the adjustable brake pedal, refer to DISC.
The braking system is a front-to-rear split hydraulic system. For additional information, refer to DISC.
The front brakes utilize a dual-piston brake caliper and disc brake system. For additional information, refer to DISC.
The rear brakes utilize a single piston caliper and disc brake system. For additional information, refer to DISC.
The parking brake system is a shoe and drum system. For additional information, refer to DISC.
The anti-lock brake system (4WABS) utilizes either a 3-channel or 4-channel system. For ABS-equipped vehicles, a 3-channel system is used. For Advance Trac -equipped vehicles, the 4-channel system is used.