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Chevrolet Silverado 1999-2006: How to Test Rear Differential

It's important to know what kind of rear differential you have so that you know how your truck will behave in different conditions. Learning how to test the rear differential is cost-effective and simple.

By Pizzaman711 - June 8, 2015

This article applies to the Chevrolet Silverado 1500 (1996-2006).

Just about every car or truck has at least one differential on it, and anyone with 4x4 truck has two. The rear differential for trucks is the one that always gets used when the truck is in motion since all trucks are rear-wheel drive. To put it simply, it consists of interlocking gears that work together to transition the rotational power from the driveshaft into the rear axles, thus causing the tires to turn. The gears inside control the ratio to how many driveshaft rotations equal one wheel rotation; the lower the gear ratio, the more power to the rear wheels coming from a stop.

Figure 1. Rear differential diagram.

Materials Needed

  • Jack
  • Jack stands

Difference Between Open and Limited-Slip Differentials

Open differentials are what you'll find in just about every base model truck because they're cheaper and lower maintenance. During normal driving conditions, both of these differentials operate pretty close to the same. They both take power from the driveshaft and turn it into power to rotate the wheels. The major difference between an open and a limited-slip differential is how they operate when driving conditions are less than ideal such as in snow or mud.

Open differentials always look to apply the most even amount of torque as possible to both of the rear wheels. This would be all you would ever need in a perfect world, but unfortunately in real-world scenarios, this provides a lot of drawbacks. If one wheel looses traction such as it being on ice or even off the ground, it takes very little torque to make that wheel spin. Since low torque is required to spin that wheel, that same amount of low torque gets applied to the wheel on the opposing side. Basically, one wheel will be turning very fast while the other will be turning barely any if at all. This leaves you in a pretty bad situation because unless you can give both wheels traction, you're most likely going nowhere.

Limited-slip differentials help to remedy that problem while still maintaining more street-able qualities than a locked differential. That's because during normal driving conditions, these function exactly the same as an open differential; it's only during low-traction situations that the difference become apparent. When traction becomes low on one wheel, clutch packs inside the differential wedge into the spider gears to transfer torque evenly. The majority of limited-slips are progressive clutch-based which means the more power applied, the more they lock the two axles together. This leads to both wheels spinning more or less at the same rate, so that one wheel with traction can hopefully pull you out.

Figure 2. Differential comparison.

Testing Differential Type

Step 1 – Check differential code

For the 96-06 Silverado's, the factory limited slip differential will have a code of G80. The RPO code should be listed inside the glove box. If you purchased the truck used or can't find the code, proceed to Step 2 for another form of testing.

Figure 3. G80 RPO code.

Step 2 – Test In low-traction situation

Depending on your current weather conditions, you can go test in a place where one wheel will have low traction. Limited-slip differentials usually require a 100-200 RPM difference between the wheels to engage, so you won't need to lay on the gas too hard to test. What you'll want to do is drive the truck so that one rear wheel is in a place with little traction such as on wet grass, in mud, or in snow. You want the other wheel to have traction, so being on pavement would be perfect.

  1. Make sure there is nothing in front of you that you can possibly hit. If you do have a limited-slip and it engages, the truck may launch a little bit from a dead stop so be prepared to hit the brakes as well.
  2. Slowly start accelerating while keeping an eye on both wheels.
  3. Once the wheel with no traction begins to spin fast enough, the limited-slip should engage. If it doesn't, you can try to accelerate a little bit more.

If the truck does not begin to move forward, you most likely have an open differential.

Figure 4. Truck stuck in mud.

Step 3 – Test in no-traction situation

Generally, a no-traction situation is when one wheel is off the ground. This is actually rather simple to test since all trucks come factory with a jack.

  1. Like in the previous step, make sure there is nothing in front of you that you can hit. DO NOT try this in your garage.
  2. Placing the jack under the axle tube on one side, raise the truck just high enough so that one wheel is off the ground and can spin without catching anything below it. You don't need to be more than .5-1" off the ground.
  3. Slowly start accelerating until the no-traction wheel begins to spin at a fast rate.

The goal here is for the limited-slip to kick in and for you to be able to easily drive off the jack. This is why you want to accelerate slowly and don't want the truck too high off the ground.

Figure 5. One wheel off the ground.

Step 4 – Open the differential

Unless you have done this before, it's recommended taking it to a qualified mechanic for this step. The differential is pretty complex inside and it's very easy to break or mis-align something that can destroy it. A qualified mechanic should be able to quickly tell what kind of differential it is.

Featured Video: How to Test Rear Differential

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