Atlas II T-Case Swap Overview

The Atlas II from Advance Adapters is the gold-standard aftermarket transfer case for serious off-road builds. Gear-driven (not chain), twin-stick (independent front/rear engagement), and available in multiple low-range ratios.

Low range options:

• 3.0:1: mild, road-friendly
• 3.8:1: balanced, popular for trail rigs
• 4.3:1: deep crawler
• 5.0:1: extreme crawler, requires fast tires or it's unusable on the road

Why Atlas:

• Gear-driven means no chain stretch, more torque capacity, doesn't 'pop' under shock loads
• Twin sticks let you run front-only or rear-only — useful in tight corners or on slick rocks
• Cast aluminum or iron case, rebuildable in field
• Multiple input/output spline options for different transmissions
• Better ground clearance than NP231 at the same skid plate height

Cost: $3500-5500 for the case plus install kit, plus driveshaft adjustments. With install, $5000-8000 total. Not cheap.

When worth it: dedicated rock crawler, hardcore trail rig, build budget that already has the basics done. Doesn't make sense on a daily driver — too expensive for the marginal road benefit.

Alternatives in the same space: Klune-V add-on (see crawl box entry), JB Conversions Super Short SYE with a high-ratio kit, or a Rubicrawler. Atlas is the most premium.

Fitment: needs a custom crossmember or skid mod. Most fabrication shops have done Atlas installs and have templates.

Why it works

• gear-driven
• twin-stick
• deep low ratios
• rebuild-friendly

Trade-offs

• expensive
• custom install
• overkill for street

Tools required

• full shop
• welder
• trans jack
• alignment fixture

Parts

Sources

• Atlas II info

Related

• Crawl Box Add-On (Tera 4:1 / Klune-V)
• NP231 Overview (1:1 / 2.72:1)
• All Jeep Cherokee XJ guides & tools
• Browse the full DIY database

Written and maintained by an AZ wheeler and driveway wrencher. How we source guides. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.