Posi, Limited-Slip, Locking Differential: Which Used Diff Do You Need?

Posi, Trac-Lok, Anti-Spin, Gov-Lok, e-Locker — every manufacturer brands their traction device differently, and parts catalogs use the terms interchangeably enough to confuse even experienced shop owners. The result is one of the most common ordering mistakes in the used differential market: a buyer asks for “a Posi” and gets shipped something that doesn’t match their truck’s original spec.

This guide cleans up the terminology, shows you exactly how to identify what you have on every major US truck platform, compares behavior across street, towing, snow, and off-road conditions, and lists used and new pricing by type. The goal is simple: when you call FirstChoice or any other supplier, you’ll know precisely which used differential you need and how to confirm the match.

Definitions for US Buyers — What Each Manufacturer Calls Their LSD

The confusion starts with brand names. Functionally these are all the same category of part — they’re either limited-slip or selectable lockers — but parts catalogs list them by their factory brand name, and getting that name right is what makes the order land correctly.

Side-by-Side Comparison: Open vs LSD vs Selectable Locker vs Auto-Locker

How to Tell What You Have — Manufacturer-by-Manufacturer Identification

GM — Chevy Silverado, GMC Sierra, Tahoe, Yukon, Suburban

Open the glove box and look at the RPO sticker (Regular Production Option). It is a white sticker with 3-character codes in columns. Look for these:

• G80 — Locking differential (Gov-Lok auto-locker on 2000-2014; Eaton helical LSD on 2015+)
• GT4 — 3.08 axle ratio (open standard, G80 available)
• GU4 — 3.42 axle ratio
• GU6 — 3.73 axle ratio
• GT5 — 3.42 HD ratio
• GU2 — 4.10 axle ratio

If your truck has G80 listed, you have an LSD or locker. If only an axle ratio code is listed without G80, you have an open differential.

Ford — F-150, F-250, F-350, Bronco, Expedition

Open the driver door and look at the certification label on the door jamb. Find the axle code — it is a two-character alphanumeric code in the bottom row labeled AX or AXLE. The code map:

• 19 = 3.55 open | L9 = 3.55 Trac-Lok
• B5 = 3.73 open | K5 or D5 = 3.73 Trac-Lok
• 26 = 4.10 open | L6 = 4.10 Trac-Lok
• X4 = 3.31 open (most common on EcoBoost F-150)

The ‘L’ prefix or ‘K/D’ substitution indicates Trac-Lok limited slip.

RAM — 1500, 2500, 3500

The SPID label (Service Parts Information) is on the radiator support, glove box, or trunk lid depending on year. Find the axle ratio code (DSA, DXA, etc.) and look up against the RAM service catalog.

• DSA = 3.92 Anti-Spin LSD
• DRA = 3.92 open
• DXA = 3.55 open
• DSB = 3.73 Anti-Spin

Toyota — Tacoma, Tundra, 4Runner

Toyota does not use a single sticker code — you have to check the trim level and confirm with the build VIN. TRD Off-Road and TRD Pro Tacomas and Tundras include either factory LSD or e-Locker. Check the dashboard for the locker switch (right of the steering wheel, near the traction control button). If the switch is present, you have an e-Locker.

Jeep — Wrangler, Grand Cherokee

Wrangler Rubicon trims have selectable Tru-Lok lockers front and rear (Dana 44). Sahara and Sport trims have either open (standard) or optional Trac-Lok LSD. Grand Cherokee trims are similar — check the build sheet or the dash for the locker switch.

Drivetrain Behavior Comparison — Street, Towing, Snow, Off-Road

Street Driving

Open and LSD differentials are indistinguishable at normal driving speeds and loads. Selectable lockers are open until engaged — same street behavior as a fully open diff. Auto-lockers (older GM Gov-Lok) occasionally chatter on tight low-speed turns when one wheel briefly loses grip — usually felt as a clunk on sharp parking lot turns.

Towing

LSD is the clear winner for trailering. Open differentials lose traction the moment one wheel breaks loose — common when pulling out of a wet ramp or a steep driveway with a loaded trailer. LSD biases torque before slip becomes a problem. Selectable lockers can be engaged briefly for boat ramps and grass starts, then disengaged for road towing.

Snow and Ice

LSD provides modestly better snow traction than open — enough to get moving from a stop in 2-3 inches without dramatic wheel spin. Lockers (engaged) are excellent in deep snow but unsafe on ice at speed — the locked rear axle wants to step out on corners. Best practice: engage locker for stuck recovery, disengage for normal winter driving.

Off-Road

Selectable lockers are the gold standard for serious off-road. Auto-lockers are second. LSD is adequate for forest service roads and light trail. Open is the worst — one wheel lifts and you’re stopped. The Jeep Rubicon’s front-and-rear Tru-Lok setup is the factory benchmark for crawl capability.

Cluster Guides

Cost Comparison — Used vs New by Type

Frequently Asked Questions