Debree shields behind rear disc brake rotor rotted out.

very likely an indication that your brake pads are completely worn out and you are damaging your brake rotor with every pedal push. Get to a brake mechanic immediately.

Rear disc brakes? My '04 KT2500 HD used similar "floating" rotors. Also, be sure to clean up or replace the metal guides the new pads ride on, mine have stuck and caused severe wear on the inside of the rotor, while the outside pad had minimal wear. I used a file to smooth up the notches on the pads and some steel wool to clean up the salvageable clip-on guides. Check the steel brake lines while you are down there for rust/corrosion, this is an issue for these trucks.

That is if you have the same braking system as the 2500, if not these guys have a series of great videos pertaining to your specific model.

http://www.youtube.com/watch?v=WH6wnmNkC0o

This is a big job for such a small part. I suggest you repair/replace rotors, pads, and anything else back there while you are at it. You will need to remove both wheels on both sides, as well as the axles (I think). See my earlier post on Rear Rotor removal to see how this is done.

You will need a large spindle nut to remove the axles.

DISASSEMBLY:
Once you have access to the parking brakes inside the rotor hat:
1. Lock out the parking brake w/a pair of Vise grips (on the parking brake cable under the cab)
2. Disengage teh park brake cable from behind the rotor assembly to allow easier disassembly of the parking brake shoes.
3. Disassemble the rear park brake shoes.

REASSEMBLY:
1. Reassemble the rear parking brake shoes. This is a typical, small brake drum configuration. Do one side at a time - so you can see how to reassemble each small part. Keep the springs and parts oriented the same: front to front and interior to interior, etc.
2. Release the parking brake cable
3. Install the disc brake rotor(s)
4. Install the disc brake caliper(s)
5. Install tire & wheel assembly
6. Lower the vehicle

didnt state what brake is causing problem and if it is constant or only under braking---if a disc brake than need to remove caliper and examine pads for proper seating and damage also piston is not seized or cocked slightly and need to check rotor -not warped as well as caliper bolt pins not bent or rusted --on a rear disk check parking brake behind at rear inside of rotor if binding can adjust brake cable------if rear drum check adjustment-retaining springs and drum for warp out of round

Removal & Installation CAUTION Dust and dirt accumulating on brake parts during normal use may contain asbestos fibers from production or aftermarket brake linings. Breathing excessive concentrations of asbestos fibers can cause serious bodily harm. Exercise care when servicing brake parts. Do not sand or grind brake lining unless equipment used is designed to contain the dust residue. Do not clean brake parts with compressed air or by dry brushing. Cleaning should be done by dampening the brake components with a fine mist of water, then wiping the brake components clean with a dampened cloth. Dispose of cloth and all residue containing asbestos fibers in an impermeable container with the appropriate label. Follow practices prescribed by the Occupational Safety and Health Administration (OSHA) and the Environmental Protection Agency (EPA) for the handling, processing, and disposing of dust or debris that may contain asbestos fibers.

The brake rotor can be removed without separating the caliper from the mounting bracket.

1. Release the parking brake.
   
2. Remove 2/3 of the brake fluid from the master cylinder.
   
3. Raise and support the vehicle.
   
4. Remove the tire and wheel assembly.
   
5. Remove the caliper and mounting bracket as an assembly.
   
6. Hang the caliper and mounting bracket assembly from the suspension using mechanics wire.
   
7. Remove the rotor. Slowly turn the rotor while pulling the rotor away from the axle. (15 series).
   
8. Remove the rotor. Slowly turn the rotor while pulling the rotor away from the axle. (25 series).
   NOTE If the rotor is stuck to the hub, try using a slide hammer to free it.
   
   

To install:
WARNING Whenever the brake rotor has been separated from the hub/axle flange, any rust or contaminants should be cleaned from the hub/axle flange and the brake rotor mating surfaces. Failure to do this may result in excessive assembled lateral run-out (LRO) of the brake rotor, which could lead to brake pulsation.

1. Thoroughly clean any rust or corrosion from the mating surface of the hub/axle flange.
   
2. Thoroughly clean any rust or corrosion from the mating surface and mounting surface of the brake rotor.
   
3. Inspect the mating surfaces of the hub/axle flange and the rotor to ensure that there are no foreign particles or debris remaining.
   
4. Install the rotor. Slowly turn the rotor while pushing the rotor towards the axle. (15 series).
   
5. Install the rotor. Slowly turn the rotor while pushing the rotor towards the axle. (25 series).
   
6. Install the caliper and the mounting bracket as an assembly.
   
7. Install the tire and wheel assembly.
   
8. Lower the vehicle.
   

on a 07 f450 and a f550 there is brake shoes in a rear drum behind the rotor the backing plate on one side has a slot on top the other side its on the bottom use a brake tool to adjust the star wheel

Your going to hate this answer. The wheel hub has to come off. This brake system was designed by Isuzu. Don't know what else to say, it's a lousy job.

spry some of bp blaster or WD-40 on the rotor then use ur hammer and it will work

REAR WHEEL BEARING/ HUB

Removal Procedure

1. Raise the vehicle. Refer to Vehicle Lifting in General Diagnosis.
2. Remove the wheel and the tire. Refer to Tire and Wheel Removal and Installation in Wheels, Tires and Alignment.
   1. Remove and support the brake caliper. Refer to Brake Caliper Replacement (Front) or Brake Caliper Replacement (Rear) in Brakes.
   2. Remove the brake rotor. Refer to Brake Rotor Replacement in Disc Brakes.
   3. Remove the ABS sensor wire connector.
   4. Remove the four bolts from the control arm.
   5. Remove the hub and bearing from the control arm.
   6. Remove the brake shield from the control arm.
   7. Clean the control arm face and the bore before installing the hub and the bearing.
   Installation Procedure
   
   Notice: Refer to Fastener Notice in Service Precautions.
   
   1. Install the brake shield and the hub and the bearing to the control arm with the four bolts. Be careful not to drop the hub and the bearing, as it could be damaged. Reconnect the ABS sensor. Tighten the hub and bearing bolts to 70 Nm (52 ft. lbs.).
   2. Install the brake rotor. Refer to Brake Rotor Replacement in Disc Brakes.
   3. Install the brake caliper. Refer to Brake Caliper Replacement (Front) or Brake Caliper Replacement (Rear) in Disc Brakes.
   4. Install the wheel and the tire. Refer to Tire and Wheel Removal and Installation in Wheels, Tires and Alignment. Tighten the wheel nuts to 140 Nm (100 ft. lbs.).
   5. Lower the vehicle.