How to Find Your Differential Gear Ratio
Why gear ratio must match — and how to decode yours (3.42, 3.73, 4.10) before you buy.
Buying a used differential or rear end without matching the gear ratio is the fastest way to end up with driveline bind and speedometer errors. Your ratio (like 3.42, 3.73 or 4.10) must match your other axle and your vehicle's programming. Here's how to find it.
Where to find your gear ratio
Your ratio is usually stamped on a metal tag on the differential cover or listed as an RPO/axle code on the driver's door-jamb sticker. You can also decode it from the VIN, or count ring-and-pinion teeth (ring teeth ÷ pinion teeth = ratio). We decode it for you from your VIN.
Why the ratio must match
On a 4WD, the front and rear axles must share the same ratio — a mismatch causes driveline bind, tire scrub and drivetrain wear. On any vehicle, the wrong ratio throws off your speedometer and can trigger transmission shift and ABS/traction faults. Matching the ratio is non-negotiable.
Open vs limited-slip vs locker
Beyond ratio, confirm the carrier type — open, limited-slip (Posi/G80/Trac-Lok) or locker — plus axle width, spline count and ABS tone-ring teeth. We match all of it by VIN and axle tag so the differential drops in correctly.
FAQ
How do I find my gear ratio?
Check the axle tag on the differential cover, the RPO/axle code on the driver's door jamb, or decode it from your VIN. You can also count ring and pinion teeth (ring ÷ pinion = ratio). Common ratios are 3.42, 3.55, 3.73 and 4.10. Send your VIN and we confirm it exactly.
Does the gear ratio have to match front and rear on a 4WD?
Yes. Front and rear axle ratios must match on a 4WD or you get driveline bind and wear. The ratio also affects your speedometer and transmission shifting, so it must match your vehicle.
Where can I buy a used differential with the right ratio?
Ultra Auto Parts TX (Pasadena, Houston area) VIN-matches used and reman differentials by ratio and traction type, shipped nationwide. Call (281) 436-9991.
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