How to Identify Your Truck Axle — Dana, Meritor & GM Guide

Before you can order the right differential parts, you need to know exactly which axle you're working on. A wrong identification leads to wrong parts — and in heavy-duty trucking, wrong parts mean wasted money, wasted time, and trucks sitting idle.

The problem is that axle identification isn't always straightforward. Tags corrode, stampings fade, and Dana, Meritor, and GM all use completely different numbering systems. This guide covers everything you need: why correct identification matters, where to find the information, how to read it, which models you're most likely dealing with, what to do when the tag is missing, and the most common mistakes to avoid.

Why Axle Identification Matters

Axle parts are not interchangeable across models — even within the same manufacturer. A carrier assembly that fits an RT40-145 will not fit an RS23-160, even though both are Meritor rear axles. A ring and pinion set for a Dana S130 won't bolt into an S150 housing.

Beyond model compatibility, the axle tag also tells you the gear ratio, differential type (standard, limited-slip, or locking), and the original Bill of Materials — all of which determine which specific replacement components you need. A 3.73 ring and pinion for a Dana 44 is a completely different part than a 3.73 for a Dana 60, even though the ratio is identical.

Getting the identification right at the start eliminates returns, avoids downtime, and ensures the correct parts ship the first time. A wrong ID doesn't just waste money on shipping — it means your truck stays off the road while you wait for the right part to arrive.

Where to Find Axle Information

Every axle leaves the factory with identification markings, but each manufacturer puts them in a different place. Knowing where to look is the first step.

Dana / Spicer

Dana axles use a Bill of Material (BOM) number as their primary identifier. It functions like a VIN for the axle — encoding the model, gear ratio, differential type, and all factory components. You'll find it in two locations:

• Metal tag on the differential cover. A stamped metal tag attached to the differential cover by two of the cover bolts. This is the easiest place to check — but tags are often removed and not reinstalled during diff cover gasket replacements.
• Stamping on the axle tube. The BOM is also stamped directly into the long axle tube (right-hand or left-hand, depending on model). These stampings are faint and often covered in grime, but they're permanent — they can't be lost during service.

The axle model number (e.g., "60" for a Dana 60, or "S130" for an HD model) is also cast into the housing on the center section web or nose of the carrier housing.

Meritor

Every Meritor axle ships with a stamped identification plate attached to the carrier or axle housing. The plate is typically located on the carrier housing, visible when looking at the axle from the front of the vehicle (toward the driveshaft side).

The Meritor ID plate contains the axle model number, serial number, gear ratio, customer part number (the OEM's spec number), and the carrier part number — everything you need to source the correct replacement components.

GM (RPO Codes)

General Motors uses a unique system: RPO codes (Regular Production Option). These three-character codes are printed on a factory sticker inside the vehicle and describe every option the truck was built with — including axle type, gear ratio, and differential configuration.

Important: RPO codes tell you the factory-original configuration. If the axle or gear ratio has been swapped since the truck left the factory, the RPO sticker will no longer be accurate.

How to Read an Axle Tag

Finding the tag is step one. Understanding what the numbers mean is step two. Each manufacturer uses a different coding system.

Reading a Dana BOM Number

Traditional Dana BOM numbers are six digits followed by a dash number, starting with 60 or 61.

Critical detail: on many tags, the leading two digits are dropped. If your tag reads 5661-1, the full BOM is actually 605661-1. You need the full 6-digit number to look up parts correctly.

Decoding a Meritor Model Number

Reading GM RPO Codes for Axle Info

On the GM RPO sticker, look for three-character codes starting with G, F, or H.

Common Axle Models

Dana / Spicer — Common Models

Meritor — Common Models

GM — Common Axle Housings

What If the Tag Is Missing?

Method 1: Visual Identification

• Differential cover shape and bolt count. This is the fastest visual check. A Dana 60 has a 10-bolt cover with a slightly rounded profile. A GM 14-bolt has a distinctive square-bottomed cover. Compare against known reference photos to narrow the field.
• Integral vs. dropout carrier. Some axles use a removable carrier (dropout design), while others have the carrier cast as part of the housing (integral). Dana 44 and 60 are dropout; GM 10-bolt and 12-bolt are integral.
• Axle tube diameter. Measuring the tube OD with calipers helps differentiate between similar-looking models in the same brand family.

Method 2: Ring Gear Measurement

Measuring the ring gear diameter and counting the number of ring gear bolts is usually enough for a definitive ID.

Method 3: VIN and Build Sheet Lookup

• Commercial Class 6–8 trucks: Contact the OEM dealer with the VIN. They can look up the original axle manufacturer, model, and gear ratio from their build records.
• GM light-duty trucks: Use an online VIN decoder to pull the full RPO code list. GM dealerships can also pull the complete RPO sheet from their system using the VIN.

Method 4: Rotation Count

1. Safely jack up both rear wheels off the ground.
2. Mark one rear wheel and the driveshaft with a reference point (chalk or tape).
3. Slowly rotate the driveshaft by hand while counting how many full turns it takes for the marked wheel to complete one full revolution.
4. That number is your gear ratio.

Method 5: Send Us Photos

Mistakes to Avoid

• Dropping the BOM prefix on Dana axles. If your Dana tag reads 5661-1, the leading "60" has been dropped. You need the full 6-digit BOM (605661-1) to look up the correct parts.
• Confusing Meritor carrier series. The 140, 141, 143, 144, and 145 series all differ internally despite similar numbering. Always match the full model number.
• Trusting RPO codes on modified vehicles. If a GM truck has had aftermarket gears, a locker install, or an axle swap, the glovebox sticker is no longer reliable. Always verify against the physical tag on the axle housing itself.
• Ordering by gear ratio without confirming the axle model. A 3.73 ring and pinion for a Dana 44 is a completely different part than a 3.73 for a Dana 60. Always confirm both the axle model and the ratio before ordering.
• Assuming the diff cover shape alone is enough. Different axle models can have similar-looking covers. Always cross-reference with bolt count, tag data, or ring gear size.
• Not cleaning the tag before reading it. Years of road grime make tags look unreadable when they're actually just dirty. A minute with brake cleaner and a wire brush often reveals a perfectly legible number.