How do I know if I have 28 or 31 spline axles?
The quickest way to know is to count the splines on the axle shaft that engages the differential: 28 splines means a 28-spline axle, 31 splines means a 31-spline axle. If you can’t see the shaft directly, check stamped codes on the axle housing or consult your vehicle’s service manual or parts catalog to confirm the spline count.
Understanding why spline count matters
Axle spline count determines how the axle shaft interfaces with the differential, as well as which lockers, carriers, and ring-and-pinion gear sets will fit. Using the wrong spline count can lead to improper fit, reduced strength, or part incompatibility. Because different axle families used by manufacturers can vary over time, it’s important to verify the exact count for your specific axle once you know the family you’re dealing with.
To determine the spline count on the axle you have, follow these steps:
- Safely lift and support the vehicle, remove the wheel and any components needed to access the end of the axle shaft, and then count the number of ridges (splines) around the circumference of the shaft where it engages the differential.
- If the end of the shaft is difficult to see, carefully rotate the shaft or remove the axle shaft assembly to expose the spline area and count the ridges accurately. Use a bright light or a loupe to avoid miscounting small teeth.
- Count the entire set of splines around the circumference; a complete 28-spline shaft will have 28 ridges, while a complete 31-spline shaft will have 31 ridges. Do not confuse partial or damaged splines with the full count.
- Record the count for both sides if applicable and compare with manufacturer charts or your vehicle’s parts catalog to confirm the exact spline count for your axle family.
Conclusion: Once you have counted the splines, you can verify against official diagrams or documentation to confirm whether you have a 28-spline or 31-spline axle.
Alternative ways to verify without counting every spline
If you can’t access the shaft easily, you can still verify via documentation, stamping, or service literature. These methods can save time and reduce the need for disassembly.
- Look for stamped markings on the axle housing or differential cover end that indicate spline count, part number, or a code mapped to a spline specification. Some manufacturers stamp a number or letter code near the end of the axle that corresponds to spline count.
- Consult the vehicle’s factory service manual, parts catalog, or the axle’s vendor documentation using the exact model year, trim level, and VIN if needed. These sources often list the spline count for that axle family.
- Check the VIN-specific build sheet or online parts databases. Entering the vehicle’s VIN or axle code can reveal the correct spline count and compatible replacement parts.
- Ask a dealership, independent mechanic, or specialty axle shop to look up the correct spline count using your exact vehicle configuration. They can confirm compatibility and recommended replacements.
Practical notes by axle family
General guidance
Many common 28- and 31-spline axles belong to well-known families (for example, certain Ford, GM, and aftermarket axles). Within a given family, there may be multiple spline variants across different years or market-specific models. Always verify with an authoritative source for your specific vehicle, as part numbers and diagrams can change over time.
What to do next
Once you’ve established the spline count, use that information to source the correct carrier, locker, ring-and-pinion, or axle shaft replacements. If you’re unsure, bring the axle or a clear photo of the end of the shaft to a parts counter or a specialty shop; they can confirm the spline count and compatibility.
Summary
In summary, the simplest method is to count the end splines on the axle shaft itself, with 28 and 31 being the two most common counts you’re likely to encounter. If counting isn’t practical, rely on stamped codes, vehicle manuals, or parts catalogs to verify the spline count. Getting the count right ensures proper fit and reliable performance when replacing or upgrading axles.
