* Check the vehicle's documentation: The original window sticker, owner's manual, or service records *might* list the axle ratio. This is the most straightforward method if you have these documents.
* Look for a tag on the differential: Some differentials have a tag stamped with the gear ratio. This tag is usually located on the differential housing itself, but it can be hard to read or may be missing.
* Visually inspect the differential (requires some mechanical knowledge): With the rear wheels off the ground and the vehicle in neutral, you can rotate the driveshaft one full revolution and count how many times the driveshaft turns the axle. This is not always perfectly accurate, as it can be difficult to get an exact count, but it will provide an estimate. Caution: Take extreme caution when working under a vehicle. Use jack stands, never rely only on a jack.
* Check the RPO codes (if you know the VIN): The RPO codes (Regular Production Option codes) listed on the vehicle's identification plate (usually located on the driver's side dashboard) might contain information about the axle ratio. However, you'll need a decoding chart to interpret the RPO codes. There are several online resources that provide this, but you'll need the VIN.
The most reliable method is to check the vehicle's documentation, followed by looking for the tag on the differential. The visual inspection method is less accurate and should only be used as a last resort.
