The 2004-2006 Pontiac GTO comes from the factory with a 3.46 gear ratio limited-slip differential. Limited slip means it is not a full true locked Posi rear end. Both rear tires are not always spinning at the same speed. They will both spin at the same time and same speed when enough torque is placed on the gears, such as pulling a holeshot or just stomping on the gas to squeal the tires.

You can download the “Rear Drive Axle” section of the service manual below. The differential is the same for all three years, 2004, 2005, and 2006 Pontiac GTO.

The rear ends on these cars are pretty sensitive to which fluid they have in them. I’m going to show which fluid works the best and how to change it.

Step 1:

Torco is by far the best differential fluid for these cars. I’ve tried stock and other synthetic brands, Torco RGO outperforms them all! If you use any brand other than Torco, I cannot guarantee your differential will not still clunk or make noises you don’t want it to. Only use Torco RGO 85w140!

And yes I realize Type F friction modifier is for Ford, Chrysler, and Toyota. But the Pontiac GTO rear end also uses a Type F friction modifier.

Step 2:
Drive your vehicle for at least 10 minutes to get the differential fluid warm. You want as much of the fluid to come out as possible when you drain it.

Step 3:
Jack up the rear end of your vehicle and place it on jack stands and look at the differential. Use the diagram  below:

• Number 1 – Differential Fluid Fill Plug
• Number 2 – Differential Fluid Drain Plug

Remove the drain plug bolt (Number 2) and drain the fluid. Be patient, let as much fluid as possible drain from the differential. You can loosen the Fill Plug (Number 1) bolt to let air into the differential for a faster drain if you wish. After the fluid has completely drained, reinstall the drain plug (Number 2) and tighten it to 20 ft/lbs (foot-pounds) using a Torque Wrench. Now completely remove the fill plug (Number 1) for the next step.

Step 4:
Using a funnel, pour no more than 2 ounces of Torco Type F Friction Modifier into the differential. Do this first.

Next, pour the Torco RGO differential fluid into the fill hole (Number 1). You will use just under 2 quarts. Fill the differential until it starts to drip out from the fill hole. When the fluid is coming out of the fill hole, the differential is full. Re-install the fill plug (Number 1) and tighten it to 20 ft/lbs (foot-pounds) with a Torque Wrench. Take the car off the jack stands and take it for a drive.

A quiet differential is a happy differential. Hope this service tip has helped. Thanks for reading!

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