* Visually Inspecting the Differential: This is the most definitive method, but requires access to the differential. Look for markings on the differential cover itself. Some manufacturers will stamp "limited slip," "posi," or a similar designation. However, this isn't always present. You'd also need to look *inside* the differential (requiring removal of the cover) to definitively see the limited-slip components. This is not recommended unless you have experience working on differentials.
* Jacking Up and Rotating the Wheels: This is a less certain but easier method. Jack up one rear wheel (if you suspect the rear differential is posi-traction), and then rotate it while observing the opposite wheel. If the opposite wheel rotates in the same direction (at the same speed, or nearly the same speed), it's a strong indication of a posi-traction or limited-slip differential. If the opposite wheel spins in the opposite direction or remains stationary, it's an open differential. Note that this test can be inconclusive in some cases, especially on newer vehicles with electronic traction control that may intervene.
* Check the Owner's Manual or Build Sheet (if available): The owner's manual or a factory build sheet (if you have one) should specify the type of differential. Look for terms like "limited slip," "posi-traction," "locking differential," or similar.
* Vehicle Identification Number (VIN) Decoder: Some online VIN decoders can provide information about the vehicle's options, including the type of differential. The accuracy of this varies by the VIN decoder and vehicle make/model.
* Look for a sticker on the vehicle: Some manufacturers place stickers in various locations (like the glove box, under the hood, or on the door jamb) that detail factory options and specifications.
Important Note: Many modern vehicles utilize electronic traction control systems that mimic the effect of a posi-traction differential. These systems engage electronically to send power to the wheel with the most traction. The jack-up test might not accurately distinguish between a true posi-traction and an electronic traction control system.
The jack-up test is the most readily available method for most people, but it's not foolproof. For certainty, consulting the owner's manual or a vehicle history report is recommended. If you still have doubts, a mechanic can perform a thorough inspection.
