The engine makes power. That power is sent from the engine to the transmission. Then the power comes out of the transmission and goes to a transfer case that sends the power to the front or the back of the vehicle through the driveshafts to the axles. Inside the axles are another set of gears called a differential, that sends the power to the tires.

Toms Offroad Options:

Dana 44 - https://tomsoffroad.com/ford/66-77-bronco-dana-44-traction-devices

Ford 9 inch - https://tomsoffroad.com/ford/66-77-bronco-ford-9-traction-devices

Selectable Lockers:

Yukon Zip Locker - Air engage locker

ARB Air locker - Air engaged

OX locker - Air or Manual (cable) shift

Limited Slip:

Yukon Grizzly Locker

Dana 44 Power Lock

Open:

Open Carrier (but you probably already have one in your Bronco)