I've got an '86 9" housing that came out of a Bronco. I am going to build it and use TrueHi9 3rd and 35 spline axles. I know nothing about 9" axles, so I have some questions. Is this housing a big bearing one and what bearings do I need? What's the best brand for chromolly axle shafts in 35 spline variety? Any other advice on building this axle?

Stock carrier bearing sizes for the 9" are 2.893” or 3.062” and many of the spools, lockers etc that are 35 spline require 3.25" carrier bearings.

You need to be careful about saying "big bearing 9" axle" because people use theat to refer to the axle bearing size like the Torino style axle housing ends. So which bearings are you asking about, carrier or wheel? The 3rd case you are using will require a specific size carrier bearing which will in turn determine which diff you choose so the stock size carrier bearing is really a moot point.

As far as axles shafts go, Superior is hard to beat. Strange is another option.

If it is an 86 bronco housing then it is a big bearing, They use tapered roller bearings on the axles instead of sealed balls. Jesse is correct about the carrier bearing sizes. I bought a strange nodular pumpkin so I could run 3.250" bearings with my detroit

Or you could use Moser or Yukon axles, But why stop there. Go warn full floating axles

If you have a big (wheel) bearing housing it should measure about 3 1/2 inches at the very end (last inch) where the brake backing plate bolts are attached. If so Randy's Ring & Pinion and possibly others should have a 35 spline axle kit that comes with axles and bearings it fit right in for ya. Then, when you order a third member just order it for 35 spline axles and you'll be all set.

Hope that helps. :D

complete offroad sells a spool that will let you use 35 spline in a stock 9" third member.