How do I identify my Ford rear axle?

In most Ford applications, the rear axle can be identified by reading the axle code tag on the differential, inspecting the housing for stamped markings, and cross-checking with the vehicle’s VIN/build data. The three most common Ford rear-axle sizes are 7.5", 8.8", and 9", and reliable identification rests on tags, measurements, and official data.

Quick identifiers you can check on the axle

These quick checks help you determine the axle family without disassembling the entire suspension. Start with any tag or stamped markings you can access safely.

• Locate and read the axle code tag or stamping on the differential. The tag typically lists the gear ratio and may be labeled as AXLE or show a numeric ratio such as 3.55, 3.73, or 4.10.


• Inspect the differential cover area for stamped numbers on the cover or housing. Some Ford differentials carry a code or ratio directly stamped where the cover meets the housing.


• Check the factory build data for your vehicle (VIN/build sticker in the door jamb or owner's manual). Decode any axle code listed there using Ford’s official catalogs or reputable online databases.

Using these tags and build data provides a reliable path to identify the axle family and its gearing without removing major components.

Visual and physical clues to distinguish common Ford axles

In addition to tags, certain visual cues help you tell whether you’re dealing with a 7.5", 8.8", or 9" Ford rear axle.

• 7.5" rear axles tend to be lighter and smaller overall, with a more compact differential housing typical of older passenger cars and light-duty trucks.


• 8.8" rear axles use a more robust, rounded differential housing and are widespread in late-1980s to present Ford cars and trucks. They often feature a larger ring-gear area and a thicker housing compared with the 7.5".


• 9" rear axles have a noticeably large center section and a removable third member that is secured with multiple bolts. They are heavier and are common in classic performance Mustangs and various Ford trucks from earlier decades.

These visual cues, when combined with tag data, give you a solid basis for identifying the axle family.

How to verify gear ratio and axle type using measurements

For projects requiring precise gearing, you can confirm the gear ratio and axle type through measurements and documentation.

• Remove the differential cover (safely) to look for stamped numbers on the ring gear or inside the carrier. The ratio may be stamped there or on a tag attached to the carrier; cross-check with Ford catalogs.


• Count the teeth on the ring gear and the pinion to calculate the ratio. If you can access both gears, the ratio is the ring-gear tooth count divided by the pinion tooth count; this can confirm whether you have 3.55, 3.73, 4.10, etc.


• Use the vehicle’s VIN/build data to confirm the factory-installed axle ratio. Enter the VIN into Ford’s official databases or trusted reference sites to retrieve the axle code and gearing.

Combining tag data, measured gear counts, and VIN-based information minimizes guesswork and ensures you’ve identified the exact axle and gearing for maintenance or upgrades.

Best practices for identifying a Ford rear axle

Always work safely: park on level ground, engage the parking brake, and use appropriate supports when lifting the vehicle. If you’re unsure about reading axle codes or removing the cover, consult the service manual for your year/model or seek a professional technician’s help.

Additionally, many Ford enthusiasts’ resources, online forums, and parts catalogs maintain up-to-date axle code lists and gear-ratio charts. These can be invaluable when you’re trying to identify an axle from photos or incomplete data.

Summary

To identify a Ford rear axle, start with the axle code tag on the differential and any stamping on the cover or housing, then corroborate with your vehicle’s VIN/build data. The three most common rear-axle sizes are 7.5", 8.8", and 9"; use tag information, physical traits, and gear-ratio markings to distinguish them. When in doubt, consult the factory service information or a qualified technician to confirm the exact axle type and gearing for your vehicle.

Additional notes for enthusiasts

If you’re planning upgrades or parts compatibility, capture clear photos of the differential area, tag, and any stamped codes. This documentation speeds up identification when contacting parts suppliers or a shop. Whether you’re restoring a classic Mustang or maintaining a modern Ford truck, precise axle identification helps ensure you choose the correct gears, bearings, and fittings.

Summary done. For readers wanting to dive deeper, consult Ford’s parts catalogs, official repair manuals, and trusted online databases to map axle codes to specific gear ratios and housing designs for your exact year and model.

How do I know what Ford rear axle I have?

Step 1: Locate the Axle Code

1. View the Safety Compliance Certification Label on the driver's side, front or rear door panel.
2. Find the word AXLE under the bar code.
3. Find the two-digit code under AXLE.

How to tell the difference between Ford 8.8 and 9.75 rear end?

You can tell the difference between a Ford 8.8 and 9.75 rear end by inspecting the differential cover and axle housing: the 9.75 has a larger, more prominent bulge on the driver's side of the cover and a more angular taper towards the passenger side, while the 8.8 has a smaller cover and a flatter housing profile. For a definitive identification, check the differential cover bolt count, which is typically 12 for the 9.75 and can be more or less for the 8.8 depending on the specific model.
 
This video explains the visual differences between the Ford 8.8 and 9.75 rear ends: 58sAxel Power's GarageYouTube · May 10, 2014
Visual inspection of the differential cover and housing 

• Differential Cover Shape: The 9.75 has a noticeable bulge on the driver's side and tapers more towards the passenger side. The 8.8 has a smaller, flatter cover without the large bulge. 
• Axle Housing: The 9.75 has a larger housing and thicker axle tubes. 

Other identification methods

• Axle Tag: The most accurate way to identify the rear end is by reading the tag on the differential. The tag will contain codes that specify the gear ratio and other information. 
• Differential Cover Bolts: Check the number of bolts holding the differential cover. The 9.75 axle has 12 cover bolts, while the 8.8 has a different number depending on the model year. 
• Ring Gear: If you can see the ring gear, the 9.75 will be larger than the 8.8. 
• Axle Spline Count: The 9.75 has 34 axle splines, while the 8.8 can have a different count depending on the model. 

What to do

• For identification: When identifying the rear end, visually inspect the differential cover and axle housing for the differences mentioned above. If that's not enough, you can also check the axle tag or count the cover bolts for a definitive answer.
• For maintenance: Correct identification is crucial for proper maintenance and to ensure you are using compatible parts. For example, selecting the wrong parts could lead to premature wear or failure. 

How do I tell if I have a Ford 9 inch rear end?

You can identify a Ford 9-inch rear end by checking for a round center section with two flat spots, using a socket to check the bottom two pinion nuts (a socket won't fit on a 9-inch), looking for a removable third member/dropout, and measuring the ring gear diameter if other methods are unclear. The 9-inch housing is known for being stronger than an 8-inch and features a different bolt pattern for axle retention, using a retainer plate with four bolts instead of the C-clip style found on other rearends.
 
This video demonstrates how to identify a Ford 9-inch rear end by checking the bottom nuts and comparing it to an 8-inch rear end: 58sAutorestomod Manic Mechanic Gasoline MediaYouTube · Sep 8, 2016
Visual and physical inspection

• Center section shape: A 9-inch housing has a more rounded, raised center section with two flat spots, while an 8-inch is generally round with two dimples at the bottom. 
• Bottom nuts (socket test): A simple and quick test is to see if a deep socket fits over the bottom two studs on the differential. On an 8-inch rear end, a socket will fit. On a 9-inch rear end, a socket will not fit, and you must use a wrench to remove the nuts. 
• Third member/dropout: The 9-inch has a removable center "third member" or "dropout" that can be serviced from the front and removed from the housing without taking the entire axle out of the car. 
• Axle retention: Look for a flat retainer plate with four bolts at the end of the axle tubes. This is how the axle shafts are secured in a 9-inch. This is a key difference from other rearends that use internal C-clips that require removing the back cover. 
• Housing characteristics: An older 9-inch may have "neck-down" tubes that taper toward the axle flanges, while newer ones maintain a consistent diameter. Some housings also have an outward swell or bump indicating a "big bearing" style, often found in trucks and larger cars. 

Other methods

• Marking tags: Look for a metal tag, often on one of the center section bolts, that contains codes including the gear ratio. The tag can also specify if the rearend is an 8-inch, 9-inch, or 9.5-inch. 
• Paint markings: Ford often used yellow or white paint to mark information on the back of the housing. 
• Ring gear measurement: If you can't access the housing, you can measure the diameter of the ring gear to confirm if it is 9 inches across. 
• Differential type: You can identify the type of differential by looking for a metal tag on one of the bolts that holds the center section to the housing, which has the gear ratio stamped on it. 

This video explains the differences in differential types between Ford 9-inch and 12-bolt differentials: 58sCurrie EnterprisesYouTube · Aug 25, 2020

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.