Climb under there and pull on the driveshafts, any movement and its a bad u joint.
If you can feel it in the pedal, chances are its not the rear drum cause the feeling wouldn't be transmitted via the brake lines. It wouldn't hurt to pull the rear drum off and investigate, the only thing that can be causing noise there would be if the springs got broken and you don't need to be a mechanic to see that. Is the parking brake operating normally?
It maybe a problem with the pedal. Look and see where it attaches to the master plunger and make sure you didn't have a pin fall out or anything. FYI the master plunger goes through the firewall to your brake pedal, so you'll be looking inside the jeep near you feet.
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2000 XJ Cherokee
1964 Ford Fairlane 500