I just picked up a new trail rig to build for relatively cheap fun. It's a 1988 Ford Bronco II with a 2.9L engine and a five-speed with a Borg Warner 1350 transfer case. The goal is to swap in a Dana 30 with a locker and upgraded axleshafts as well as an 8.8-inch rear out of an Explorer. I’ll probably run 5.13 gears and 33s. Do you think the Dana 30 will live? Any information and suggestions would be appreciated.
The baby Broncos have a small but loyal following, and their compact size makes them a good choice for trail work. The engine isn’t exactly a powerhouse, but it gets the job done while being reliable. The FM145 transmissions and BW1350 transfer cases are adequate as long as you don’t go crazy on engine power or tire size.
For the front axle, we would look for a non-disconnect, reverse-cut Dana 30 out of a Cherokee, which should be plentiful and cheap in your local junkyards. We would steer clear of a disconnect Dana 30 from a YJ or early XJ unless someone just gave you one for free, as these have a two-piece passenger-side axleshaft that is weaker than a traditional one-piece design and the TJ applications had low-pinion center sections. The Cherokee axle will give you the right wheel bolt pattern and is pretty much spot-on in terms of width. There will be some fabrication involved in adapting the front axle to the radius arm suspension design, but it’s not too bad. James Duff (dufftuff.com) has cast axle wedges suitable for use with any donor axle, and the company can even help on the track bar as well. An early Bronco housing would also be a good option, but not the cheapest one. Bronco Dana 44s and even open-knuckle Dana 30s command pretty decent money these days, and the wheel bolt pattern is 5-on-5 1/2. Lockers and gears are plentiful for both Dana 30s and 44s.
For the rear axle, you can’t go wrong with a disc-brake 8.8 out of a Ford Explorer. We trip over a dozen or more of them every time we go to the junkyard, so you can afford to be picky and find one that is complete. Axle prices vary from region to region, but our local self-serve yards charge about $160 for a complete axle assembly. The 8.8 is the right width and wheel bolt pattern, making it a no-brainer.
Your transmission’s First gear is 3.72:1, and your transfer case has a low-range of 2.48:1. You didn’t mention what kind of terrain you’re planning on getting into, but this is on the lower end of ideal for technical rockcrawling with 33s. Your only real option with the stock stuff is to go as low as you can on the axle gears, so you’re limited to 5.13s with a Dana 30 frontend. Those gears will net you a respectable but unremarkable 47:1 crawl ratio. The Dana 30 should live just fine with 33s and the 2.9L engine, even with a locker. If you’re planning on being really hard on the Bronco, then chromoly shafts and heavy-duty axle joints are a wise choice.