http://www.supermotors.net/getfile/617247/fullsize/bronco2.jpg

You can see the " 6"-8" pieces of channel" here:
http://broncograveyard.com/images/catalog/7TALREGBRACKET.JPG

What stevesnaz is talking about is the Window Regulator Bracket (http://broncograveyard.com/bronco/i-34555_window_regulator_bracket__on_bottom_of_windo w_.htm), which is actually two pieces: the support bracket which is riveted to the glass, and the channel piece which acts as a guide for the regulator . If you have a lot of corrosion on the regulator bracket, simply lubing it may not do the trick. Mine was so corroded that the Regulator Roller (http://broncograveyard.com/bronco/i-24548_regulator_roller__tailgate__each.htm) was destroyed. I ended up replacing both the channel and the roller. I probably could have cleaned up the channel with a wire wheel but the bolt broke off when I removed the channel from the support bracket.

There is also a good chance that simply lubing up the channel will fix your problem, but you need to get in there and look at it. If you plan on un-bolting the glass make sure you soak the bolts for a while in PB first (if they are rusty), one of mine snapped off with very little torque. Thankfully I alread had the new one on hand so I simply bolted the new one in, replaced the Roller (its actually square and doesn't roll at all, it slides in the channel) and put it all back together.