How to Identify Your Axle and Gear Ratio

You can identify most axles in about ten minutes by reading the axle tag, checking your vehicle's factory codes, or counting the ring-gear and pinion teeth. If you are still unsure, send us your VIN and photos, and we can confirm most axles before you order.

What you'll need

Write down your vehicle's year, make, model, engine, 2WD or 4WD, and whether the unit is front or rear. Then gather:

  • A flashlight, a wire brush and a rag
  • Chalk or a paint marker
  • A tape measure
  • A drain pan and basic hand tools, only if you plan to open the axle for a tooth count

Support the vehicle on jack stands or drive-on ramps and chock the wheels. Never get under a vehicle held up by a jack alone.

Method 1: Read the axle tag or ID code

Start here, because it is the fastest check. Clean the axle housing and cover with a wire brush, then look for a metal tag, a sticker or stamped numbers.

  • Metal tags are often held on by one of the cover bolts.
  • Codes may be stamped into the axle tube or housing near the cover.
  • Some tags show the gear ratio directly. Others show a code that has to be looked up.

Take a clear photo of anything you find and send it to us, and we will decode it. Tags go missing, get painted over, or belong to an axle that a previous owner swapped or re-geared, so treat a tag as a strong clue and confirm it with a second method.

Method 2: Count the ring-gear and pinion teeth

Gear ratio is the number of ring-gear teeth divided by the number of pinion teeth. A ring gear with 41 teeth and a pinion with 11 teeth gives 41 ÷ 11 = 3.73. The same ring gear with a 10-tooth pinion gives 4.10, and with a 12-tooth pinion gives 3.42.

  1. Support the vehicle level on jack stands and set a drain pan under the axle.
  2. Remove the cover bolts, let the fluid drain, and take off the cover.
  3. Mark one ring-gear tooth with chalk, then count every tooth around the large gear.
  4. Count the teeth on the pinion, the small gear at the end of the driveshaft.
  5. Divide the ring-gear count by the pinion count.
  6. Reinstall the cover with a new gasket or sealant and refill the axle with fluid.

If your axle has no removable cover, or you would rather not open it, use the driveshaft spin test below.

Method 3: The driveshaft spin test

This gives you the ratio without opening the axle, and it is accurate enough to tell a 3.73 from a 4.10.

  1. Lift the axle so both wheels are off the ground and supported on jack stands. Put the transmission in neutral, put the transfer case in neutral if you have one, and release the parking brake.
  2. Mark the driveshaft with chalk or tape, and mark one tire at the top.
  3. With a helper, turn both tires together in the same direction for one full revolution while you count how many times the driveshaft turns. That count is your ratio. A count of about 3.7 turns points to a 3.73.
  4. Repeat the test a few times and average the results.

You can also hold one tire still and turn the other for one revolution, then double the driveshaft count. Limited slip and locking units can behave differently with one wheel held, so turning both tires together is the more reliable method. On AWD vehicles, contact us before relying on this test.

Method 4: VIN, build sheet and factory codes

Your VIN identifies the vehicle, but it does not always identify the axle. Factory codes and build records get you closer:

  • Ford: the safety certification label on the driver's door jamb includes an axle code.
  • GM: the Service Parts Identification sticker, often found in the glove box, lists option codes, including axle ratio and differential type.
  • Ram, Dodge and Jeep: a dealer can often pull a build sheet from the VIN.

These codes show what left the factory, not necessarily what is in the vehicle today. Send us the VIN and any codes you find, and we can match them to the right unit.

Method 5: Cover shape, bolt count and ring-gear size

Three physical checks narrow the field once the axle is cleaned up:

  • Cover shape: note whether the cover is round, oval or irregular, and whether it has a flat edge or a bulge.
  • Bolt count: count the cover bolts. Many different axles share a bolt count, so this narrows the choices but rarely settles them on its own.
  • Ring-gear size: the inch size in our product titles, such as 8.6-inch or 11.5-inch, is the diameter of the ring gear. With the cover off, measure across the ring gear and match it to the title.

If you only do one thing, photograph the cover and the tag straight on and send the photos to us through Contact Us.

Identify your axle by make

Our catalog lists each unit by ring-gear size, so once you know the size you can match it to the right listing. The table shows what we carry today. Many models appear with more than one axle in the same years, so confirm with the methods above and do not rely on the model name alone.

Make Rear axles in our catalog Front axles in our catalog
Chevrolet and GMC 8.0 (Colorado), 8.5, 8.6, 9.5 and 11.5-inch 7.25, 8.25 and 9.25-inch
Ford 8.8, 9.75, 10.25, 10.5 and 11.5-inch (Dana 80), plus a 9-inch dropout with locker 8.8-inch and Dana 50
Dodge and Ram 8.25, 9.25, 10.5, 11.25, 11.5 (AAM) and 11.8-inch 8.25, 9.25 and 9.5-inch
Jeep Dana 35, Dana 44 (JK Rubicon) and 8.25-inch (Grand Cherokee) Dana 30 and Grand Cherokee WK
Toyota Tundra and Land Cruiser Tacoma, Tundra and T100

Watch for these when you match a listing:

  • Same truck, same years, different axle. A 1988–1998 Chevrolet 1500 appears with an 8.5-inch rear and with a 9.5-inch heavy half-ton 6-lug rear. Ford F-150s from 1997 to 2007 appear with 8.8-inch or 9.75-inch rears. A 2003–2004 Dodge Dakota appears with an 8.25-inch or 9.25-inch rear.
  • Drive type. Some listings split by 2WD, 4WD, AWD or dual rear wheels (DRW), so note these when you write down your vehicle.
  • Limited slip. Many sizes are listed both standard and with limited slip. If you are not sure which you have, or which type you need, read our guide to limited slip vs. locking differentials or contact us.
  • ABS. Some Jeep listings specify ABS, so check whether your vehicle has it.

Shop by make:

We also carry units for Cadillac, Lincoln, Mercury, Buick, Hummer and Nissan. The same steps apply.

Front or rear, and what to send us

Front and rear axles are separate units, so identify each one on its own. On 4WD and AWD vehicles the front and rear gear ratios should match, so check both before you order either.

When you contact us, send as much of this as you have:

  • Year, make, model, engine, and whether the vehicle is 2WD, 4WD or AWD
  • Front or rear
  • The VIN
  • The axle tag or stamped code, and any factory codes
  • Tooth counts or your spin-test result
  • Photos of the tag and the cover
  • Options such as limited slip, a locker, a towing package or dual rear wheels

Frequently asked questions

How do I tell what rear end I have?

Look for an axle tag or stamped code on the housing, then confirm the ring-gear size and gear ratio by counting teeth or doing the driveshaft spin test. Your VIN and factory codes help, but they only show what the vehicle had when it was built. Send us your VIN and photos, and we can confirm most axles.

How do I find my gear ratio without opening the axle?

Use the driveshaft spin test. With both wheels off the ground and the transmission in neutral, turn both tires together for one full revolution and count how many times the driveshaft turns. That number is your gear ratio. You can also read it from the axle tag or factory codes.

Can my VIN tell me what axle I have?

Not by itself. A VIN identifies the vehicle, but the same model and year can come with more than one axle. Use the VIN together with the axle tag, factory codes or a tooth count.

What if my axle tag is missing?

Count the ring-gear and pinion teeth, or do the spin test, to get the ratio. Then measure the ring gear and note the cover shape and bolt count to find the size. You can also send us photos of the cover and we will help narrow it down.

Do my front and rear gear ratios have to match?

On 4WD and AWD vehicles, yes, in most cases. If the front and rear ratios differ, the axles turn at different speeds, which strains the drivetrain and can cause damage. Check both ratios before you order.

What does "8.6-inch" or "10-bolt" mean?

The inch size is the diameter of the ring gear. The bolt count is the number of bolts holding the cover on. Many axles share a bolt count, so the ring-gear size is the more reliable way to tell them apart.

I changed my tire size. Does that change my gear ratio?

The ratio is set by the gears inside the axle, so tires do not change it. Larger tires do make the gearing effectively taller, which can dull acceleration and towing. If you have gone up in tire size, tell us the new size and we can help you choose a ratio.

Not sure? We can help you confirm

If the numbers do not add up or you cannot reach the axle, call 719-460-7267 or contact us with your VIN and photos and we can confirm most axles before you order. We ship nationwide from Pueblo, Colorado, and have been remanufacturing differentials and transfer cases for over 35 years. Every unit is rebuilt in-house.

Ready to shop? Browse all differentials or transfer cases.

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