I had a 1962 AMC Rambler. It had borg warner overdrive that worked really well. I could run 75 mph highway speeds with no problems. Does anyone have any experience with theses things? I'm wondering why this can't be done to my 3 speed manual 1973 bronco.

You'd have to "squeeze" it between the trans & the t-case, or make your Bronco rear wheel drive.

4R70W automatic with OD or a ZF5 manual with OD seem to be best way to get an OD into a Bronco. You'll need to regear the axles or your highway RPM will be too low and lug down the motor.

Welcome to the club from Gunnison! Good to see some more western slope folks. I know there are a lot of Broncos out here. Post up some pics of your truck!

Yeah, on 2WD rigs, something like this is less complicated, but as Gunni said, sticking a box between the tranny and t-case opens a big can of worms in regards to mounts and driveshaft issues.

There were bolt on units made back in the day for Dana 20's, but I wouldn't recommend using one on a rig that is destined for off road use and big tires.

I have a rancho overdrive unit in storage. It bolts on in place of the rear output assembly on the d20.

I'm just figuring out how to navigate this site. Thanks for the replys. When I figure out how to include photos of this rig, I will. I do like the idea of the zf transmission except for having to put a body lift of 1.5-2 inches.

I'm installing a ZF & Atlas right now without a body lift. But I am cutting a lot, and haven't even dry fitted the Atlas. You'd need a body lift to do it without chopping it up. For a little money, and wiring you can do the 4R70W automatic without a body lift.

What gears, tire size are you running now?

The tires are 31x11.5
Not sure of the gearing. I've got to cut out some of the floor pan anyway since the areas where your feet would rest are rusted through. May as well cut a new hole for a new 5 speed tranny. Again, thanks for your reply. I'm not going to waste any more time thinking about the overdrive.