The first generation Ford Bronco came with either a Dana 30 or Dana 44 front axle. The Dana 30 was used from 1966 to mid-year 1971. At this point in 1971, Ford made the switch to the beefier Dana 44 front end and continued this through 1977, the last year of the early Bronco. In 1976 and 1977, Ford equipped the Dana 44 with disc brakes. All early Broncos prior to 1976 came with factory drum brakes
The easiest way to identify which front end you have in your early Bronco is to look at the steering knuckles. The Dana 30 uses king pins which are held in with four bolts on the top and bottom. The Dana 44 uses ball joints which are held in with large castle nuts.
While rare, there were a certain number of Broncos delivered with "hybrid" axles that used Dana 30 outer components with king pins and a Dana 44 center section and gears. These were found primarily on '69 and '70 model Broncos and the only way to tell for sure what you have in those cases is to verify the front cover design. The Dana 30 has a concentric shape, and the Dana 44 had an offset shape.
Note: All of the parts in this illustration will not apply to all years. Identify your front end and then check the part description for proper application.
There are 3 different spindles that were used from 66-77. All Bronco Dana 30's and 71-72 1/2 Dana 44's use a spindle with the spindle/outer axle seal pressed into the back of it. These have 6 bolt holes. The 72 1/2-75's do not have the spindle/outer axle seal pressed into the back. It is located on the outer axle seal flange which is pressed onto the outer axle itself. These also have 6 bolt holes. The 76-77 disc brake spindle is easily identified by its 5 bolt holes. All new spindles come with spindle bearings.