How can I tell what rear axle I have in my F-150?

The quickest way is to read the axle ratio printed on the driver’s door jamb sticker or on the rear differential tag. You can also confirm by decoding your Vehicle Identification Number (VIN) or by checking the original window sticker or build sheet.

In practical terms, most F-150 owners can identify their rear axle by (1) inspecting the door sticker for an “AXLE” line or ratio, (2) inspecting the differential housing or tag for a stamped or labeled ratio or housing size (such as 8.8" or 9.75"), or (3) using the VIN to pull drivetrain details from Ford’s official resources or a dealer. The exact location and labeling can vary by model year and trim, so it’s useful to check multiple sources if one is unavailable.

Where to look on the vehicle

Below are the most reliable, hands-on methods for identifying your F-150’s rear axle without needing specialized tools.

• Door jamb sticker: Look on the driver’s side door frame for a line labeled AXLE or Axle ratio. Common values are numbers like 3.55, 3.73, or 4.10. If the sticker lists an axle code rather than a numeric ratio, you may still be able to decode it using Ford’s codes for your year and trim.


• Differential housing tag or stamp: On many F-150s, a tag or stamped marking on the rear differential (the cover or the axle housing) indicates the axle size (for example 8.8" or 9.75") and sometimes the gear ratio (3.55, 3.73, etc.).


• Rear axle/tire area markings: Some models include a small placard or stamped numbers near the brake line or on the axle tube itself that identify the axle size or ratio. These can be easy to read with a flashlight and a clean surface.


• Original window sticker or build sheet: If you have access to the vehicle’s original Monroney sticker or the build sheet, the axle specification is listed there along with the drivetrain and options.


• Dealer or service records: If you’ve bought the vehicle recently or have access to the dealer’s records, the axle ratio is often included in the service history or the vehicle’s spec sheet.

Knowing where to look helps you confirm the rear axle without disassembling anything, and it can be particularly important when ordering parts or planning upgrades.

Interpreting the numbers

The numbers you see refer to either the axle housing size (8.8-inch, 9.75-inch, etc.) or the gear ratio (for example 3.55, 3.73, 4.10). The left-to-right relationship matters: the axle size tells you the physical housing, while the ratio tells you how many times the driveshaft turns for each wheel revolution. If you see a code rather than a numeric ratio on the door tag, you’ll need a reference for that year and trim to translate the code into a ratio or axle type.

Using the VIN and documentation

If you can’t read the axle from the sticker or the differential, decoding the VIN or pulling the build data from official sources will give you a definitive answer.

1. Locate the VIN: It’s stamped on the dashboard near the windshield on the driver’s side, and also on the driver’s door jamb label. Note the full 17-character sequence.


2. Use Ford’s official VIN decoder or your dealer’s system: Enter the VIN to retrieve drivetrain details, including the axle ratio or axle code associated with that vehicle.


3. Look for drivetrain or axle entries: The decoder should display fields such as “Axle,” “Axle Ratio,” or “Drivetrain.” If the exact ratio isn’t shown, note the axle type (for example, 8.8" or 9.75") and confirm the ratio with a dealer if needed.


4. Cross-check with other documents: Compare the VIN-derived data with the door sticker, window sticker, or build sheet for consistency.


5. When in doubt, call the dealer: Provide the VIN and request the original equipment list or the build sheet, which will include the axle specification.

VIN-based verification is particularly reliable for confirming an axle when the physical labels are faded or missing, and it can be the easiest way to resolve discrepancies between different sources.

Tips for different model years

Ford has used a few different label formats over the years. If you’re looking at a pre-2015 F-150, the 8.8" or 9.75" rear axles were common, with the door sticker often including a straightforward axle ratio. In later models and higher-trim packages, the axle information might appear as an axle code rather than a number. In those cases, the VIN decode or a dealer lookup will be the most dependable path to an exact figure.

Summary

Identifying your F-150’s rear axle is typically straightforward: check the driver’s door jamb sticker for the AXLE/ratio, inspect the differential housing or tag for the size and ratio, or consult the original window sticker/build sheet. If those sources aren’t readable, use the VIN with Ford’s official decoder or contact a dealer to pull the drivetrain details. With the axle type and ratio known, you’ll be better prepared for maintenance, part matches, and any planned upgrades.

How do I identify my Ford rear differential?

To identify a Ford rear differential, look for a metal tag or adhesive label on the differential housing, which contains a code indicating the ring gear size and ratio. If the tag is missing, you can identify it by counting the cover bolts, measuring the ring gear diameter or housing width, or by performing a manual spin test on the wheels to check the differential type (open or limited-slip). 
This video shows how to decode a Ford axle tag: 50sBSK GarageYouTube · Oct 23, 2020
Using the identification tag or label 

• Location: Tags are typically bolted to a cover bolt, while modern labels are often found on the axle tube near the wheel. 
• Reading the code: The bottom line of the tag/label often contains the most crucial information, such as a gear ratio (e.g., "3.00" or "3L00" for a locking differential) and the ring gear size (e.g., "8.8" for an 8.8-inch axle). 
• Resources: You can use online resources like FORDification.com to decode the full axle code, which includes application and year information. 

This video shows how to identify the differential type by spinning the wheels: 55sAutorestomod Manic Mechanic Gasoline MediaYouTube · Sep 8, 2016
Identifying without a tag

• Counting cover bolts: The number of bolts holding the differential cover on can help narrow down the type (e.g., the Ford 9-inch has 10 cover bolts). 
• Measuring components:
  • Ring gear size: This is the diameter of the large gear inside the differential. A "9" indicates a Ford 9-inch, and "8.8" indicates an 8.8-inch. 
  • Housing width: Measure the distance between the axle flanges on each axle tube. Ford 9-inch differentials came in several widths, from 57-1/4" to 69-1/4". 
• Differential type (open vs. limited-slip/locking):
  • Lift the rear of the vehicle so both wheels are off the ground. 
  • Spin one rear wheel. 
  • Open differential: If the wheel spins freely in one direction, the other wheel will spin in the opposite direction. 
  • Limited-slip/locking differential: If the wheel spins freely, the other wheel will spin in the same direction. 

This video explains the visual difference between Ford 7.5 and 8.8 rear ends: 56sRegular Car ReviewsYouTube · Oct 30, 2015

How do I find out what rear axle I have?

It's worth noting that rear axles can sometimes be positively identified by a casting number and date stamped on the differential cover or axle tube.

How do you tell if you have a 7.5 or 8.5 rear end?

You can tell the difference between a 7.5 and 8.5 rear end by looking at the shape of the cover, the shape of the axle tubes, and the protrusions on the bottom of the housing. The 8.5 has a round cover with larger, rectangular protrusions at the bottom, while the 7.5 has a more squared or oval cover with smaller, crescent-shaped lugs at the bottom. Additionally, the axle tubes on an 8.5 are flared or stepped down as they enter the pumpkin, while the 7.5 has straight axle tubes.
 
This video shows how to visually identify a GM 10 bolt rear axle, including how to distinguish between a 7.5 and 8.5 rear end: 53sandhotrodshopYouTube · Dec 14, 2023
Visual differences

• Cover shape: An 8.5 has a round rear cover, whereas the 7.5 has a more squared-off or oval cover. 
• Axle tubes: The tubes on an 8.5 will appear to swell or flare out just before entering the differential housing. The 7.5 has straight axle tubes. 
• Bottom protrusions: The 8.5 has larger, rectangular "ears" or protrusions at the bottom of the housing (around the 5 and 7 o'clock positions). The 7.5's protrusions are smaller and more crescent-shaped. 

Other methods

• Measure the bolts: On some GM 10-bolt rears, the distance between the bottom center bolt and the nearest bolt on either side can be used for identification. 
  • 8.5: The distance is approximately 3.753.753.75 inches. 
  • 7.5: The distance is approximately 3.253.253.25 inches. 
• Check the vehicle's RPO codes: Look for a sticker in the driver's side doorjamb or glove box. The codes listed under "Axle" or "RPO" will specify the factory-installed rear end. This is the most accurate method if the rear end is original. 

How do I know if I have a 3.73 or 4.10 gear?

And since we live in the day and age of 2025. Uh if you're curious. You can easily. Google you know uh the number of teeth on a ring gear.