Impact protection where the factory left a soft spot, plus extra fluid capacity on many designs. A holed cover ends a trip fast — gear oil leaves quickly, and the gearset eats itself if you keep driving. The honest tradeoff: a thick cover adds weight low on the axle and does nothing for weak internals. Cheap insurance for rocky terrain; optional for graded roads.

After — always. Welding burns coatings off both the part and the housing, so paint applied early is paint applied twice. The working order is fit, weld, grind, degrease, prime, topcoat, including the seams and edges where moisture likes to start. Plan on the truck being down long enough for coatings to cure properly, because rushed paint over hot steel doesn't last.

If you have to ask, split the job. These parts carry real loads, and a cracked bead on an axle truss is worse than no truss, because you'll trust it. The sensible middle path: do the teardown, prep, fit-up, and paint yourself, then pay a professional welder for the structural passes. You keep most of the savings without gambling the housing on your practice hours.

Axle tube diameter, first and always — reinforcement is contoured to specific tube sizes, and identical-looking trucks can hide different axles. Confirm the axle model from tags or casting numbers, note prior modifications like relocated brackets, and eyeball where the new part lands relative to control arms, sway bar mounts, and brake lines. Five minutes with calipers prevents the classic wrong-radius return.

Usually not on day one — trusses and gussets matter most with big tires, lockers, and repeated hard hits. But loaded overlanding has its own failure mode: gear weight plus a few thousand miles of washboard fatigues brackets and factory welds in slow motion. If you run heavy on corrugated roads, reinforcing your platform's documented weak points is reasonable insurance. Fix known failure points; skip the rest.