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To adjust the ebrake on your 2003 Expedition, There is a rubber plug about an inch long behind the Brake rotor, Remove this plug. Through the hole stick a flat type screwdriver in and there is a star wheel adjuster. Turn the adjuster until the ebrake hols the vehicle
You are correct, They have rear disc brakes on your vehicle. The ebrake shoes are a drum set up and are located inside the rotor. If you remove the rotor yo will see the drum ebrake setup.
Here is a picture to help you better understand: Click on the picture
Kyle, there is no rubber plug to remove and adjust the parking brake, please advise, I just spent some time under the truck and there is nothing there like that.
There should be one behind the backing plate towards the bottom. You have to look behined the wheel on the backside were the axle goes into the rotor. The plug is on the backing plate not the rotor
I have also seen only a select few times, where Ford has forgot to stamp out the steel in the backing plate. So you may have to remove the rotor which is just 2 bolts to remove the caliper.