How do I tell what gear ratio my Chevy rear end has?

The quickest way is to read the axle tag or code on the differential, or to pull the build sheet or VIN data to confirm the ratio. If those aren’t available, you can determine it by counting ring-and-pear teeth or by comparing engine RPM to driveshaft RPM at a known speed.

For Chevy rear axles, the gear ratio is a key spec that affects acceleration, towing, and tire choice. Vehicles across generations—from older Chevys to modern trucks—use a few common methods to identify this number. Here’s how to find it, with practical steps you can follow at home or with a quick trip to a shop.

Where to look for the axle information

Chevy rear ends usually provide the ratio on a data tag or stamping on the differential housing. If the tag is unreadable or missing, other sources such as a build sheet or VIN-based decode can confirm the ratio. The exact location can vary by model and year, so check both the differential and the vehicle’s documentation.

Axle tag or stamping

Many GM axles carry a small tag on the differential cover or a stamped/embossed code on the housing that explicitly lists the gear ratio or an axle code that maps to a ratio. The tag may read “RATIO” or simply display the digits of the ratio (for example, 3.73, 4.10, etc.).

• Inspect the differential cover for a metal tag or engraved data that names the ratio.


• Look for stamped numbers on the housing near the fill plug that correspond to a GM axle code you can decode.


• Check the vehicle’s build sheet, window sticker, or glove-box data label for an axle/RPO code that references the exact ratio.

These cues are the fastest and most reliable when the data tag is legible and original to the vehicle. If you can’t read or find the tag, move on to other verification methods.

VIN/build sheet or documentation

If the tag isn’t accessible, use the vehicle’s VIN to pull the original axle configuration from GM’s databases or a reputable decoder. Build sheets or option labels (often found in the glove box or trunk) frequently list the axle ratio alongside other drivetrain options.

• Use a trusted online VIN decoder or contact a GM dealership to retrieve the axle option list from the VIN.


• Match the axle/RPO code to a published ratio in a decoder guide or GM service literature.

VIN-based or documented sources are generally precise, especially for vehicles with original equipment, but may require some cross-checking with the car’s paperwork or a dealer lookup.

How to determine the ratio by physical measurement

When tags and documentation aren’t available, you can determine the ratio by direct measurement. This approach involves either counting the teeth on the gears or using engine-to-shaft RPM comparisons. Both methods require care, a clean workspace, and reassembly with proper gaskets and fluid.

Counting teeth on the ring and pinion

This direct method yields an exact ratio by comparing the number of teeth on two gears inside the differential: the ring gear and the pinion gear.

• Drain the differential and remove the cover to expose the gears, cleaning them thoroughly so teeth are clearly visible.


• Count the teeth on the ring gear (the larger gear that meshes with the pinion).


• Count the teeth on the pinion gear (the smaller driving gear).


• Calculate the ratio by dividing the number of ring teeth by the number of pinion teeth. For example, 41 ring teeth divided by 12 pinion teeth equals 3.416, which you’d round to 3.42.

Note that aftermarket gears or shims can alter the count, so be sure you’re counting the actual gear teeth. Afterward, reseal the cover and refill the differential with the correct gear oil.

RPM method (engine RPM vs driveshaft RPM)

This method estimates the ratio by comparing engine speed to driveshaft speed at a known road speed. It works best when you know the trans gearing and avoid overdrive complications, since modern automatics can muddy the calculation.

• With the transmission in a 1:1 gear (common in certain gears or when overdrive is disengaged), drive at a steady speed (for example, 60 mph) and note engine RPM from the tachometer and driveshaft RPM with a separate measurement or tach.


• Compute the ratio as engine RPM ÷ driveshaft RPM. If the transmission is in 1:1 gear, this value approximates the final drive ratio. If you know the transmission’s gear ratio in that setting, adjust accordingly to obtain the final drive ratio.

This method is best as a cross-check rather than a primary measurement, particularly on vehicles with complex transmission gearing, torque converters, or aftermarket modifications.

Additional options and tips

• Consult the owner’s manual, build sheet, or window sticker for the axle option and ratio if the vehicle is stock.


• Ask a GM dealership or a certified shop to decode the VIN for the original axle configuration if you don’t find a tag.


• Be mindful of variations: different trims or factory options can result in different ratios even within the same model year.

When in doubt, cross-check multiple methods to confirm the ratio before planning mods that depend on the final drive, such as tire changes or gear swaps.

Summary

Finding your Chevy’s rear-end gear ratio is usually straightforward: read the axle tag or data code on the differential, or decode a build sheet or VIN. If that data isn’t accessible, you can determine the ratio by counting ring-and-pinion teeth or by a careful RPM comparison with the transmission in 1:1. Each method has caveats, especially with aftermarket gears or modern automatics, but used together they provide a reliable picture of your final drive ratio. Knowing the ratio helps you pick the right tires, plan gear swaps, and optimize performance and efficiency.

How to find gear ratio on Chevy rear end?

Identify your GMC or Chevrolet rear end gear ratio by the RPO Codes, usually located on the placard labeled “Service Parts Identification” inside the drivers door panel or glove box.

How do you tell if you have 3.73 or 4.10 gears?

You can tell if you have 3.73 or 4.10 gears by manually counting, checking the differential cover for a tag, or finding the ratio stamped on the ring gear. The most direct method is to lift the rear wheels, rotate one tire one full revolution, and count how many times the driveshaft turns; 3.75 turns indicates 3.73 gears, while slightly over 4 turns indicates 4.10 gears.
 
This video demonstrates how to check your gear ratio by counting the driveshaft turns: 48sBent Motorsports OffroadYouTube · Sep 22, 2023
Method 1: Manual count (with the vehicle jacked up)

1. Jack up the vehicle: Safely lift the rear of your vehicle and secure it on jack stands. Ensure the wheels are off the ground. 
2. Mark the driveshaft and a tire: Place a mark on one of the rear tires and a corresponding mark on the driveshaft. 
3. Rotate the tire: Rotate the marked tire forward one full revolution. For an open differential, you may need to lift only one wheel and have someone hold the other stationary, or lift both wheels and rotate one tire twice while the other tire is on the ground. For a locked differential, lift both rear wheels and have one tire rotate once while the other rotates once in the opposite direction. 
4. Count the driveshaft turns: Count how many times the mark on the driveshaft has rotated. 
   • 3.73 gears: The driveshaft will turn approximately 3.753.753.75 times for one full tire revolution. 
   • 4.10 gears: The driveshaft will turn a little over 444 times for one full tire revolution. 

Method 2: Check the differential cover tag 

1. Locate the tag: Look for a small metal tag that is usually bolted to the differential cover. It may be on one of the bolts. 
2. Read the ratio: If the tag is still present, the gear ratio will be stamped on it. It will likely be a number like "3.73" or "4.10". 

You can watch this video to learn how to find the differential cover tag: 51sFlawed OffroadYouTube · Apr 18, 2022
Method 3: Read the ring gear stamps 

1. Locate the ring gear: This requires removing the differential cover to get a clear view of the ring gear.
2. Find the numbers: Look for two numbers stamped on the teeth of the ring gear, such as "41" and "11". 
3. Divide the numbers: Divide the larger number (teeth on the ring gear) by the smaller number (teeth on the pinion gear). 
   • 41÷11≈3.7341 divided by 11 is approximately equal to 3.7341÷11≈3.73 
   • 41÷10=4.1041 divided by 10 equals 4.1041÷10=4.10 

This video shows how to read the ring gear stamps to find the gear ratio: 46sJL LIFE OFFROADYouTube · Nov 18, 2022

How to figure out gear ratio without pulling cover?

You can figure out a gear ratio without opening the cover by marking a tire and the driveshaft, lifting the vehicle, and counting the driveshaft's rotations while you turn the tire one full revolution. The number of times the driveshaft rotates is your gear ratio. For an open differential, you may need to lift only one wheel and can multiply the driveshaft's rotation by two.
 
Method 1: One full tire rotation 
This is the most accurate method and works for all differentials. 
This video demonstrates the one full tire rotation method: 1mChris DukeYouTube · Nov 22, 2016

1. Lift the vehicle: Jack up the vehicle so the drive wheel(s) can spin freely. 
2. Mark the parts: Use a marker, chalk, or tape to mark a spot on the driveshaft and a corresponding spot on the tire. 
3. Turn the tire: Rotate the marked wheel one full revolution (360 degrees). 
4. Count driveshaft rotations: Count how many times the mark on the driveshaft rotates during the tire's single revolution. 
5. Determine the ratio: The number of times the driveshaft rotated is your gear ratio. For example, if it rotated 4.5 times, you have a 4.56 gear ratio. 

Method 2: Open differential method (two revolutions)
This method can be used on vehicles with an open differential and eliminates the need for multiplication. 

1. Lift one wheel: Jack up only one of the rear wheels, leaving the other on the ground. 
2. Mark the driveshaft: Mark a spot on the driveshaft. 
3. Turn the tire: Rotate the lifted wheel two full revolutions. 
4. Count driveshaft rotations: Count the number of times the mark on the driveshaft rotates. This number is your gear ratio. 

Method 3: Reading the tag (if available)

1. Look for a tag: Check the differential cover for a metal tag that may have the gear ratio stamped on it.
2. Check the VIN sticker: Look at the VIN sticker on the driver's side door jamb for an axle code. You can then look up this code online to find the factory gear ratio. 

Important considerations

• Accuracy: For a more accurate reading on Method 1, a gear ratio between common numbers like 3.55 and 3.73 will require you to estimate the fraction of a rotation. For example, a quarter turn is 0.250.250.25, a half turn is 0.500.500.50, and three-quarters is 0.750.750.75. 
• Vehicle type: Ensure the vehicle is in neutral with the parking brake disengaged before you begin. 
• Other methods: If these methods don't work, you may need to consult your vehicle's original window sticker (Monroney) or build sheet, which will often list the gear ratio. 

Does the VIN number tell you the gear ratio?

You may be able to tell the gear ratio from a vehicle's VIN by using an online VIN decoder, though not all manufacturers include this information in the VIN itself. If the gear ratio is included, it will likely be in the Vehicle Descriptor Section (VDS), which are the 4th through 8th digits of the VIN. For many vehicles, a sticker on the driver's side door jamb or on the vehicle's build sheet or owner's manual is a more reliable way to find the gear ratio. 
How to check the VIN

• Use an online VIN decoder: Enter the full VIN into a free online decoder. Some manufacturers have their own decoders, such as Mopar's decoder. 
• Look for the gear ratio code: Some VINs will have a code within the VDS that represents the gear ratio (e.g., "3731"). 
• Consult the manufacturer: If the VIN decoder doesn't provide the information, contact the vehicle manufacturer for assistance. 

Other methods to find the gear ratio

• Check the vehicle sticker: Look for a sticker on the driver's side door jamb or on the vehicle's build sheet. This sticker often contains detailed information about the vehicle's equipment, including the axle ratio. 
• Look at the differential: Some differentials have a metal tag with the gear ratio stamped on them, or there may be a sticker on the axle itself. 
• Consult your owner's manual: The owner's manual or other paperwork from the vehicle's purchase often lists the gear ratio.