While the Diff Is Open: Lockers & Upgrades

The work that's nearly free during a regear and painful later — lockers, shafts, seals, and the carrier question.

A regear pays the differential labor bill once. Everything on this page is priced by that fact: during the job, the carrier is on the bench and the axles are out — so the marginal labor for these items is close to zero. A month later, each one costs a full teardown again.

Lockers — the headline decision

Lunchbox locker (~$450/axle, parts): replaces the spider gears inside your existing carrier. Mechanical, always working, slightly uncivilized on pavement. During a regear it adds minutes, not hours.
Selectable locker (~$1,000–$1,300/axle installed during a regear): replaces the carrier entirely (which conveniently also answers the carrier-break question if your ratio crosses one). Air lockers need a compressor; e-lockers need wiring. Both are invisible until switched on.
Rear first if budget forces a choice: a locked rear does most trail work; the front matters most in rocks and off-camber climbs.

The inspection list

The diff being open is also a diagnostic opportunity. A good installer checks — and you should ask about — axle-shaft splines (twist shows before failure), unit bearings, pinion and axle seals (replace them; they're out), and the breather (clogged breathers push oil past brand-new seals once gears run hot).

Shafts: the honest rule

Stock shafts tolerate stock lockers on moderate tires. The combination that breaks shafts is selectable lockers + 37s + a heavy right foot on high-traction rock. If that's your build, chromoly shafts belong in the same conversation as the lockers — not after the first trail repair.

What to skip

Skip truss kits, diff covers with fins, and gear ratios bought for tires you don't own yet. The open diff rewards mechanical necessities, not catalog enthusiasm.

The Decision System carries this as a working checklist synced to your shopping list, so the locker decision and the parts order can't drift apart.