Getting under your rig to perform a gear swap or a locker install can be an exciting weekend project. However, nothing kills the momentum faster than realizing you ordered parts for a Dana 35 when you actually have a Dana 44. Knowing how to identify a dana axle is the first skill every off-roader and DIY mechanic should master.
You might think all differentials look the same when they are covered in trail mud and road grime. Fortunately, Dana Spicer axles follow a very specific logic that makes identification straightforward once you know where to look. This guide will help you pinpoint your axle model with absolute certainty using visual cues and serial numbers.
We will walk through the “Holy Grail” of identification—the Bill of Materials (BOM) number—and look at the physical characteristics of common housings. By the end of this article, you will be able to crawl under any Jeep, truck, or SUV and know exactly what drivetrain components you are working with.
The Importance of Accurate Axle Identification
Identifying your axle correctly is about more than just satisfying your curiosity as an owner. If you plan on upgrading to chromoly axle shafts or installing a selectable locker, the tolerances are incredibly tight. Even within the same model family, variations in spline count or carrier offset can make parts incompatible.
Safety is also a major factor when you are out on the trail or hauling a heavy load. Overloading a Dana 35 while thinking it is a Dana 44 can lead to a snapped shaft in a remote location. Knowing your equipment’s limits allows you to drive with confidence and technical awareness during difficult recoveries.
Finally, accurate identification saves you money by preventing “restocking fees” from online parts retailers. Most drivetrain components are heavy and expensive to ship back if you make a mistake. Learning how to identify a dana axle today ensures that your hard-earned money goes toward the right performance upgrades the first time.
Locating the Bill of Materials (BOM) Number
If you want 100% accuracy, you need to find the Bill of Materials number, commonly referred to as the BOM. This is a unique string of digits stamped directly into the metal of the axle tube by the manufacturer. It is the most reliable way to determine the original gear ratio and internal specifications.
To find the BOM, look at the long side of the axle tube, usually on the passenger side for most domestic vehicles. You may need a wire brush and some brake cleaner to reveal the stampings through the rust. The number usually starts with a “6” and is followed by several digits, such as “605491-2.”
Once you have this number, you can enter it into the Dana Spicer online catalog or a trusted drivetrain database. This will tell you the exact year, make, and model the axle was built for. It also reveals the ring gear diameter and the original spline count of the shafts.
Cleaning the Axle Tube Safely
When searching for the BOM, never use a heavy grinder or a flap disc, as you might accidentally “shave” the numbers off the tube. Use a hand-held wire brush or Scotch-Brite pad to gently remove surface scale. If the numbers are faint, try shining a flashlight at a shallow angle to create shadows in the stampings.
Always wear safety glasses when cleaning under a vehicle to prevent falling rust and debris from hitting your eyes. If the axle is particularly greasy, a degreaser like Simple Green or a dedicated parts cleaner will help. Once the metal is bare, you might also find the build date stamped near the BOM.
How to identify a dana axle by Cover Shape and Bolt Count
If the BOM is too rusted to read, you can often identify the axle family by looking at the differential cover. Dana axles have a very distinct “stop sign” or “oval” shape depending on the model. Most standard Dana units utilize a 10-bolt pattern to secure the cover to the housing.
A Dana 30, commonly found in the front of Jeep Wranglers, has a smaller, more oval-shaped cover. The Dana 44 features a more angular, hexagonal shape that looks like a flattened stop sign. If you see a massive, heavy-duty housing with a large 10-bolt cover, you are likely looking at a Dana 60 or Dana 70.
Keep in mind that some aftermarket covers can change the silhouette of the differential. Always look at the flange of the housing where the bolts go in rather than the outermost shape of the cover itself. This flange shape is the “DNA” of the axle and cannot be changed by bolt-on accessories.
Counting the Bolts
While 10 bolts are standard for the most popular Dana models, there are exceptions in the heavy-duty world. For example, the Dana 80, found in dually trucks, uses 10 bolts but is significantly larger in scale. Conversely, some non-Dana axles like the Corporate 14-bolt are easily distinguished by their higher bolt count.
If you count 12 bolts, you are likely looking at a GM or specialized heavy axle rather than a standard Dana unit. If you count 10 bolts but the cover is perfectly round, you might have a Chrysler 8.25. Learning how to identify a dana axle involves recognizing these subtle geometric differences in the casting.
Reading Casting Numbers on the Differential Web
Another “pro tip” for identification is looking at the casting numbers located on the “web” of the differential housing. The web is the reinforced triangular area where the axle tubes meet the center pumpkin. Manufacturers often cast the model number directly into this area for easy sorting at the factory.
Look for a large “30,” “44,” or “60” cast into the lower right or upper left corner of the housing. This isn’t as precise as a BOM number, but it confirms the axle family immediately. It is a great way to perform a quick visual inspection when you are at a junk yard or looking at a used rig for sale.
Be aware that some “Next Generation” Dana axles (like the AdvanTEK series) might have different casting locations. On newer JL Wranglers, the casting marks are often located on the top of the housing. Using a mechanic’s mirror can help you see these hidden numbers without dropping the entire axle.
Interpreting Other Casting Marks
You might also see letters like “HD” or “CF” near the model number. “HD” typically stands for Heavy Duty, indicating thicker axle tubes or larger bearings. “CF” often refers to the foundry location where the iron was poured, which is less important for part ordering but interesting for enthusiasts.
If you see “REV” or “R” cast into the housing, this may indicate a reverse rotation or high-pinion design. High-pinion axles are prized by off-roaders because the driveshaft connects higher up, keeping it away from rocks. Identifying these marks helps you understand the specific strength and clearance advantages of your setup.
Identifying Axles via Metal Identification Tags
When these axles left the factory, they usually had a small metal tag bolted to the differential cover. This tag is a goldmine of information if it is still present. It typically lists the gear ratio and the BOM number in a stamped format that is easier to read than the axle tube.
For example, a tag might read “3 73,” which indicates a 3.73 gear ratio. If there is an “L” between the numbers, like “3 L 73,” it signifies a Limited Slip Differential (LSD). This tells you that you need to use a friction modifier in your gear oil when you perform maintenance.
Unfortunately, these tags are often discarded during the first fluid change or lost to corrosion over decades of use. If your tag is missing, don’t panic; you can still fall back on the BOM or physical measurements. If the tag is present, consider cleaning it with a wire brush and spraying it with clear coat to preserve it for the next owner.
Common Dana Models and Their Applications
Understanding where these axles are typically used can help you narrow down your search. Dana Spicer axles are the backbone of the American 4×4 industry, appearing in everything from compact SUVs to 1-ton work trucks. Each model is designed for a specific torque load and tire size.
The Dana 30 is the “entry-level” solid axle, found in the front of most Jeep Wranglers and Cherokees. It is lightweight and efficient but usually limited to 33-inch or 35-inch tires. If you are looking at a front axle in a light-duty SUV, it is very likely a Dana 30.
The Dana 44 is the “sweet spot” for many off-roaders, offering a balance of strength and weight. It appears in the rear of many Jeeps and the front of 3/4-ton trucks from the 70s and 80s. When learning how to identify a dana axle, the Dana 44 is the one you will encounter most frequently in the enthusiast community.
Heavy Duty: Dana 60, 70, and 80
When you move into the world of 1-ton trucks and extreme rock crawling, the Dana 60 takes center stage. It features a massive 9.75-inch ring gear and 35-spline shafts in many configurations. You can spot a Dana 60 by its massive knuckles and large 10-bolt cover that dwarfs the Dana 44.
The Dana 70 and 80 are strictly rear-axle affairs for heavy towing and dually applications. These housings are incredibly thick and designed to handle the massive torque output of modern diesel engines. If your truck has dual rear wheels, there is a high probability you are running a Dana 80 or a comparable heavy-duty unit.
Internal Identification: Spline Counts and Gear Ratios
Sometimes, the outside of the axle doesn’t tell the whole story, especially if a previous owner has performed upgrades. To be 100% sure of what you have, you may need to remove the differential cover. This allows you to inspect the ring gear and count the splines on the axle shafts.
The spline count refers to the number of “teeth” on the end of the axle shaft that slides into the side gears. A standard Dana 35 usually has 27 splines, while a Dana 44 can have 19, 30, or even 33 splines. Knowing the spline count is critical when ordering a new locker or replacement shafts.
While the cover is off, look at the edge of the ring gear. Manufacturers often stamp the tooth count directly into the steel. For example, if you see “41 11,” you divide 41 by 11 to get a 3.73 gear ratio. This is the only way to verify the ratio if the external tags are missing.
Checking for a Locker or LSD
While the gears are exposed, check the carrier (the part the ring gear bolts to). A standard “open” differential will have visible spider gears inside. A Limited Slip Differential will have a pack of clutches tucked behind the spider gears, often held in place by a “Z” or “S” shaped spring.
If you see a solid metal block or a complex mechanism with wires or air lines, you have an aftermarket locker. Identifying these internal components is just as important as identifying the housing. It ensures you use the correct gear oil and understand how your vehicle will handle on slippery surfaces.
Frequently Asked Questions About How to Identify a Dana Axle
How can I tell the difference between a Dana 35 and a Dana 44?
The easiest way is the cover shape. The Dana 35 is very oval and “egg-shaped,” whereas the Dana 44 has a more distinct hexagonal, stop-sign shape. Additionally, the Dana 35 usually has a rubber fill plug, while the Dana 44 typically uses a threaded metal plug.
Where is the BOM number located on a front axle?
On most front Dana axles, the BOM is stamped on the passenger side axle tube, facing forward or slightly upward. You may need to move steering stabilizers or brake lines out of the way to get a clear view of the stampings.
Can I identify my axle using the vehicle’s VIN?
The VIN can tell you what axle the vehicle was originally equipped with, but it won’t account for swaps. Many older 4x4s have had axle swaps over the years. Physical identification using the casting marks or BOM is always more reliable than a VIN search.
What does “High Pinion” mean in Dana identification?
High Pinion (HP) means the pinion gear enters the housing above the centerline of the axle shafts. This is common in Ford front axles and is highly desirable for better ground clearance and improved driveshaft angles in lifted vehicles.
Is a Dana 44 always better than a Dana 30?
Generally, yes. The Dana 44 has a larger ring gear, larger pinion shaft, and often thicker axle tubes. However, for a daily driver on 31-inch tires, a Dana 30 is perfectly adequate and slightly lighter, which can help with fuel economy and handling.
Final Thoughts on Axle Identification
Mastering how to identify a dana axle is a rite of passage for any serious automotive enthusiast. It moves you from being a “parts changer” to a knowledgeable mechanic who understands the mechanical soul of their machine. Whether you are hunting through a junkyard or preparing for a major build, these skills are invaluable.
Always remember to prioritize safety when working under your vehicle. Use high-quality jack stands, work on a level surface, and never rely solely on a hydraulic jack. Taking the time to clean your housing and read the numbers correctly will save you hours of frustration in the long run.
Now that you know what to look for, grab a wire brush and a flashlight and head out to your driveway. Identifying your gear ratio and axle model is the first step toward your next great off-road adventure. Stay safe and keep wrenching!
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