wy058 is right about the steering box getting loose.
Even the older full size FoMoCo cars used that type of steering box (if not the SAME one).
Its easy enough to adjust the gear mesh to reduce the slack somewhat, but it usually doesn't help very much for the following reason.
ALMOST ALL wear to the gears happens in the range of mesh where the steering wheel is slightly off center to centered, (where the gears are positioned almost all the time) so you can't simply crank the adjuster down to eliminate play while the steering wheel is in that middle position, or you may not be able to turn the wheel out of that centered range.
And just shy of
that point you hit a range where you can steer ok, but the steering wheel doesn't want to return by itself. If you leave it THAT way, the bearings are overloaded and you'll cause damage to the box and accelerate wear to the power steering pump.
So, if you DO try it, a simple way to do the adjustment is in very small increments (1/8 turn) and drive around for a while, making left and right turns at slow speed, (preferably in a big parking lot) between adjustment, checking for steering wheel return with your hands loose on the wheel or better still off.
Here's a link to a write up of the full procedure if you want to do it the
BEST way.
Guys; Please post -Correct Way- to adjust the steering box ***** on Bronco
www.broncozone.com
Another thought.,
Once you do fix the current problem you might consider adding a steering stabilizer if you don't already have one. It would help some with wheel darting from tread catching on grooved or broken pavement or when crossing open grid steel bridges-if you have any of those).
(The last are even more fun on a
motorcycle with blocky tread, if you can't cross em at an angle)