How do I know if my Ford 8.8 is limited-slip?

The quick answer is that you can tell by looking for a factory LSD label or by a simple wheel-spin test with the axle supported; if the wheels turn together under load, you likely have a limited-slip unit, while opposite or free-spinning wheels point to an open differential. If you’re unsure, check the axle code or factory documentation to confirm.

Understanding the question in more detail requires knowing that Ford’s 8.8-inch rear axle has been offered in several configurations over the years. Some 8.8s were open differentials, others used Ford’s clutch-type Trac-Lok limited-slip, and a few applications could feature lockers installed either at the factory or as aftermarket options. Because the presence of LSD depends on model, year, and trim, a reliable answer usually comes from one or a combination of visual cues, documentation, and a controlled manual test.

Ways to identify a limited-slip 8.8

Below are reliable, non-destructive methods to determine whether your 8.8 is limited-slip without pulling the cover.

• Visual labels or stamping: Look for a tag or engraving on the differential carrier or cover that says “Trac-Lok,” “LSD,” or “Limited Slip.” Some axles also carry small abbreviations like “TL” or “LSP” near the fill plug.


• Axle-code cross-reference: Find the axle code stamped on the axle tube or a build-tag and cross-reference it with Ford’s axle-code charts or reputable online databases to see if LSD is indicated.


• Cover markings and factory documentation: Some models show “LSD” or “TRAC-LOK” on the differential cover itself, and the original window sticker or build sheet can list the LSD option.


• Model/year context: Certain model-years and trims were more likely to have LSD as a factory option; consulting Ford service literature for your exact year can help confirm.

Using these cues will help you verify LSD status without disassembly. If you find a clear LSD designation, you’re dealing with a limited-slip unit; if you don’t, you may have an open diff or an aftermarket locker that isn’t labeled the same way.

Hands-on testing to confirm limited-slip

If you prefer a practical check, perform a controlled wheel-spin test with the vehicle safely supported. This can confirm LSD behavior without opening the differential.

1. Prepare the car: Park on a flat surface, set the parking brake, chock the wheels, and raise the rear axle on jack stands with the transmission in neutral and the engine off.


2. Test one wheel at a time: Grasp one rear wheel and rotate it by hand. Watch the opposite rear wheel:


3. If the other wheel turns in the same direction with noticeable resistance as you rotate the first wheel, you likely have a limited-slip (LSD) differential.


4. If the other wheel turns in the opposite direction or spins freely with little resistance, you likely have an open differential. Note that some LSDs require a small amount of initial torque to engage, so very light turns may not show full engagement.

Safety reminder: never work under a vehicle that isn’t securely supported, and keep hands and clothing clear of moving parts. If you’re unsure or uncomfortable, seek a professional inspection.

Interpreting axle codes and factory documentation

Beyond visual tags, your axle’s coded data can confirm LSD status. Here’s how to use it effectively:

• Locate the axle code: On many Fords, a stamped axle code can be found on the axle housing or near the differential. The code encodes the carrier type and sometimes the ratio; cross-reference with Ford’s charts or credible online resources.


• Check the build sheet or VIN: If you have access to the vehicle’s original build sheet or VIN-derived documentation, look for LSD or Trac-Lok listings. Dealers can pull up factory option codes from the VIN to confirm if LSD was installed.


• Match the ratio with likely LSD configurations: Some ratios were paired with LSD more often than others; while not definitive alone, a matching code/ratio pairing increases confidence in an LSD-equipped axle.

These steps help you confirm LSD status even if a physical tag isn’t obvious. If the code explicitly indicates Trac-Lok or LSD, you’re dealing with a limited-slip unit; otherwise, you may have an open differential or an aftermarket locker that requires closer inspection.

What to do if you still can’t tell

If the information isn’t clear from tags, codes, or a wheel test, consider these options:

• Remove and inspect the differential cover with caution or have a professional inspection done to observe the clutch packs or locker mechanism.


• Consult a Ford dealership or a trusted axle specialist with your VIN, build sheet, or axle code; they can confirm the original spec and whether LSD was included.


• Consider a controlled upgrade or replacement if you’re aiming for a specific traction setup, such as an aftermarket locker or a known LSD variant, especially if you’re optimizing for off-road or high-performance use.

Professional confirmation is especially helpful for older models where documentation may be incomplete or where aftermarket modifications obscure the original configuration.

Summary

Determining whether a Ford 8.8 rear axle is limited-slip involves a mix of quick checks and methodical verification. Look for designation tags or clear LSD markings, cross-reference the axle code with official charts or build sheets, and perform a safe wheel-spin test with the axle supported. If you’re unsure after these checks, consult a dealer or axle specialist to confirm your axle’s configuration. Knowing whether you have an open diff, an LSD like Trac-Lok, or a locker helps you plan maintenance, repairs, and driving strategy more accurately.

How to read Ford 8.8 axle tag?

To read a Ford 8.8 axle tag, look for a two-part code: the ratio and limited-slip code and the production/build date code. The ratio code is typically on the bottom line and includes numbers for the gear ratio (e.g., 373) and often an "L" for limited-slip differentials. The build date code provides information on the axle's manufacturing plant, date, and other details.
 
How to read the tag

• Find the tag: The tag is usually a small metal tag held by one of the differential cover bolts, or it may be a sticker on the axle tube. 
• Decode the ratio/limited-slip code:
  • The first two digits usually represent the gear ratio, e.g., 373373373 for 3.733.733.73. 
  • If there is an "L" between the first two digits, it indicates the axle has a limited-slip differential, e.g., 3L733 cap L 733𝐿73. 
  • The last digits can identify the specific model or application of the axle. 
• Decode the production/build date code:
  • The first number often corresponds to the manufacturing plant. 
  • The subsequent numbers can indicate the year, month, and day of manufacture. 
• Other information on the tag: Some tags also contain information about the correct oil weight and viscosity, as well as any required additives. 

You can watch this video to learn how to identify Ford differential housing tags: 1mYukon Gear & AxleYouTube · Nov 24, 2015
Example tag breakdown
A tag that reads 3L73883 cap L 73883𝐿7388 would indicate: 

• Ratio: 3.733.733.73
• Limited-slip: Yes, due to the "L"
• Axle size: 8.88.88.8 (the "88" at the end)

What to do if the tag is missing
If the tag is missing, you may need to remove the third member to find the gear ratio and limited-slip information, or you can look up a vehicle's VIN to find the original factory-equipped axle ratio and type.

How do you tell the difference between limited-slip and non limited-slip axles?

A limited slip axle (LSD) allows both wheels on an axle to receive power, even if one wheel has less traction, by biasing torque to the wheel with more grip. A non-limited slip (or "open") axle sends all power to the wheel with the least traction, which causes that wheel to spin uselessly and leaves the other wheel without power. The main differences are performance and cost: limited slip axles improve traction and stability but are more expensive and complex, while open differentials are simpler, cheaper, and fine for normal driving.
 
This video explains the difference between an open differential and a limited slip differential: 1mdriving 4 answersYouTube · Apr 9, 2021
Limited slip axle (LSD)

• How it works: Uses clutches or gears to limit the speed difference between the two wheels, so if one wheel starts to slip, it sends more power to the other wheel. 
• Advantages:
  • Better traction in slippery conditions (snow, ice, rain). 
  • Reduces understeer when accelerating out of a corner. 
  • Improved handling and control during aggressive driving. 
• Disadvantages:
  • More complex and expensive than open differentials. 
  • Can wear out over time, especially the clutch packs in some designs. 

This video explains how a limited slip differential works: 1mAustin CoulsonYouTube · Feb 23, 2019
Non-limited slip axle (open differential) 

• How it works: Allows wheels to spin at different speeds, which is ideal for turning, but if one wheel loses traction, all power goes to that spinning wheel. 
• Advantages:
  • Simpler design and lower manufacturing cost. 
  • Smooth and predictable handling on dry roads. 
• Disadvantages:
  • Poor traction in low-grip situations. 
  • One wheel can spin while the other does nothing, leaving the vehicle stuck. 
  • Can lead to understeer. 

This video explains how to check if your car has an open differential: 55s1974chevrolet C10YouTube · Feb 21, 2021
How to tell which you have

• Check for a tag: Look for a tag on the differential that says "use only limited slip differential fluid," which indicates you have an LSD. 
• The wheel spin test:
  • Jack up both rear wheels so they are off the ground. 
  • Spin one wheel.
  • If the other wheel spins in the same direction, it's a limited slip. 
  • If the other wheel spins in the opposite direction, it's a standard (open) differential. 

How do I know if I have a Ford 8.8 differential?

The ID tag can be your friend. It will tell you the gear ratio, rearend style, and whether it has limited-slip. Also on the tag is an ID number, which, until 1985, included four to five letters, no numbers. Almost all 8.8s—and all post-1986 Ford rearends—have letters and numbers.

How do I know if my Ford has a limited slip differential?

You're probably looking at an open differential. Now this truck. You saw we had a limited slip.