You may brake an axle, but it really depends on how you drive it. I used stock rear axles for quite a long time before they finally broke with 33x12.5" tires and a spool in the rear. With an open/unlocked rear end you will save a lot of wear and tear on the vehicle. in light trail and road use you will probably never break a thing. But each person is different so your mileage may vary.
One may s-curve the rear springs while performing climbs and on rocks, I actually ripped the spring pads off of the rear axle due to climbing up hills in 2wd when the front end wasn't working properly. Every now and then the rear tires would catch traction and I would pull the front end off the ground. Great fun. The installation of a traction bar will fix that issue.
There are quite a few ways to build a rig. You can go with Toyota axles, Ford 9" or Dana 44's, or just beef up the stock units. Only time and research will help you decide what is best for you. I recommend checking out the Readers Ride section and reading up on some of the builds in the Builds section to see what other people have done. Don't be afraid to ask questions, most of us are happy to put in our 2 cents.
