Do you ever hear a clunking noise coming from your differential? You will hear it when you either switch from park to drive or drive to reverse. That noise means it’s definitely time to change your differential fluid.
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.
| DOWNLOAD (.pdf format) |
| 2004-2006 Pontiac GTO REAR DRIVE AXLE Section of the Service Manual |
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.
| Note: If your differential was rebuilt and has the Eaton TrueTrac Limited Slip Posi differential, you do NOT need to use a friction modifier.
Taken directly from the Eaton website: What kind of oil should I use for my Detroit Truetrac? Can I use synthetic? Do I need friction additive/modifier?
Visit Eaton FAQ’s for more information here: EATON Detroit TrueTrac FAQ’s |
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.
| SPECIAL NOTE: I will warn you before pouring in the Torco RGO. Unfortunately, Torco RGO does not come with an easy pour spout on its bottles. The RGO is extremely thick and hard to pour. I recommend either finding a screw-on pour spout that fits these bottles or pouring the RGO into an empty differential fluid bottle that does have an easy pour spout. |
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!
Submitted on 11/11/22 at 7:52 am
Thank You for recommending the Torco Oil with Torco Friction modifier. Now my rear end is quiet. My car was purchased new in 2007 and has never had diff fluid changed. I had my Chevrolet dealer here in Scottsdale Arizona do the service with my Torco fluids. Wow, no more clunks or noises. What a product. Thank You for Your knowledge of these vehicles.