1. The Build Sheet (Most Reliable): If you have the original window sticker or build sheet for the truck, it will specify the rear axle ratio and possibly the type (e.g., Dana 80, AAM 11.5). This is the most definitive method.
2. The Door Jamb Sticker (Potentially Helpful): The sticker on the driver's side doorjamb might list some information about the drivetrain, including the rear axle ratio (e.g., 3.55, 3.73, 3.92, 4.10). However, it likely won't specify the exact axle type.
3. The Differential Tag (Most Common Method): Locate the differential cover on the rear axle. There should be a tag riveted or bolted to it. This tag will usually have the axle ratio stamped on it (e.g., 3.55). Sometimes, you might find a partial axle code or other identifying information. The information might be incomplete to identify the exact model, but the ratio is crucial.
4. Visual Inspection (Least Reliable): While less reliable, a visual inspection of the rear differential can provide *some* clues. The size and overall design can offer hints, but this is highly subjective and unreliable for positive identification. You would need considerable experience to make a confident guess this way.
5. VIN Decoder (Potentially Helpful): You can use a VIN decoder (many are available online, some free, some paid) to get some drivetrain information. While not always perfectly accurate, it may provide clues about the rear axle. This is less reliable than the differential tag.
After finding the axle ratio (e.g., 3.92):
Once you've found the ratio, you can begin narrowing down the possibilities. Common rear axles for a 2003 Dodge Ram 1500 4x4 include:
* Dana 80: A very heavy-duty axle, typically found in higher-payload or heavier-duty trucks. Less common in the 1500 series.
* AAM 11.5: A common heavy-duty axle for this generation of trucks.
Without the differential tag or a build sheet, definitively identifying the *exact* axle model will be difficult. The axle ratio is the most critical piece of information for gear selection and other maintenance tasks.
Remember to jack up the rear end and support it securely before performing any inspection under the vehicle. Safety first!
