All Mustang Parts
Not sure how to identify your rear-end ratio? See our guide on How to Find Your Rear End Gear Ratio.
Your Mustang's rear-end gear ratio affects how it pulls, cruises, and feels on the road. If you need to find rear end gear ratio after a swap, or you just want to find rear gear ratio on a stock car, the steps below will help. Start with the easy checks first, then move to the deeper ones only if needed.
Whether you want to identify factory gears, verify a past gear swap, or pick new gears, it helps to know the real ratio before you buy parts or make changes.Here are the most common ways to find gear ratio in your vehicle:
Looking for Mustang-specific axle codes? See our Mustang Gear Ratios & Axle Code Chart.
Start with the small metal tag on the diff housing. It can show the axle type, gear ratio, and whether the diff is limited-slip. If the ratio is listed on the tag, this is often the fastest way to find it.
Keep in mind that the tag shows the car's original setup. If the gears or the whole rear end were swapped, the tag may not match what is in the car now.
Example Of A Full Tag Code : WFCR-3D183L0875S271D
This is broken down as follows:
Most vehicles have a factory axle code on the vehicle ID label, often on the driver-side door jamb. This code points to the rear axle that was installed at the factory.
Once you have the code, you can use the maker's docs or axle-code charts to find the matching gear ratio and diff type.
The VIN can help with the car's original setup, but it does not always show the gear ratio directly. You can use the VIN to look up build data, such as the original axle assembly or option package.
This is helpful when the axle tag is missing or the car has not been changed.
Another way to estimate the ratio is to count how many times the driveshaft turns compared with the rear wheel. If the driveshaft turns about 3.73 times for one full wheel turn, the rear end likely has 3.73:1 gears.
Make sure the car is safely supported before you do this test. The result can change based on the diff type.
Know what type of diff you have before you use the wheel-turn test. With an open diff, one wheel can turn on its own, which can give a false reading if only one wheel is moved. Turn both wheels the same direction, or hold one wheel still and multiply the driveshaft turns by two.
A limited-slip diff helps share power between both wheels. That usually makes the rotation test more steady, even though the exact steps can still change by model. The clearest check is that if the other wheel spins the same direction when you turn one, it’s a limited-slip; if it spins the opposite way, it’s open. For limited-slip both wheels turn together, so the driveshaft count is the actual ratio. A worn clutch-type unit can behave like an open diff, so the wheel-direction check is worth checking.
If the tag, axle code, or rotation test does not give a clear answer, remove the diff cover and inspect the gears. The ring gear and pinion may have stamped marks or numbers that point to the original gear set.
You can also count the teeth on each gear and divide the ring-gear teeth by the pinion teeth. For example, 41 ring-gear teeth and 11 pinion teeth equal a 3.73:1 ratio.
If you need to find gear ratio after a swap, this is the most direct check.
Question: What is the easiest way to identify a Mustang's rear-end gear ratio?
Short answer: The easiest method is usually the rear-end tag, if it is still there. It may list the ratio, axle type, ring-gear size, build data, and whether the car had Traction-Lok. Just remember that it shows the original setup.
Question: Why might the axle tag or factory axle code be wrong for the current gear ratio?
Short answer: The tag and code show how the car was built. If a past owner swapped gears, changed the axle assembly, or replaced the diff, the old tag may not match what is in the car now.
Question: Can the VIN always tell you the rear-end gear ratio?
Short answer: No. The VIN may help you find build data, but the gear ratio is not always coded into it. It works best when the car is still close to stock and the axle tag is missing.
Question: Why does open vs. limited-slip matter when counting turns?
Short answer: An open diff lets one wheel turn on its own, which can skew a wheel-turn test if only one wheel is moved. A limited-slip diff usually makes the test more steady because it helps both wheels work together.
Question: How can the gear ratio be confirmed if tags, codes, and rotation tests do not help?
Short answer: Remove the diff cover and inspect the ring gear and pinion. Marks on the gears may identify the ratio. You can also count the teeth and divide the ring-gear count by the pinion count; 41 divided by 11 equals 3.73:1.
