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 hole shot, 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.
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 other 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 Type F friction modifier.
Note: If your differential was rebuilt and has the Eaton TrueTrac Limited Slip Posi differential, you do NOT not need to use 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
Drive your vehicle for at least 10 minutes to get the differential fluid warm. You want as much as the fluid to come out as possible when you drain it.
Jack up the rear end of your vehicle and place on jack stands. And look at the differential.
* 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 fluid has completely drained, re-install drain plug (Number 2) and tighten to 20 ft/lbs (foot-pounds) using a Torque Wrench. Now completely remove the fill plug (Number 1) for the next step.
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 pour the RGO into an empty differential fluid bottle which does have an easy pour spout.|
Next, pour in the Torco RGO differential fluid into 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 the fill hole, the differential is full. Re-install the fill plug (Number 1) and tighten to 20 ft/lbs (foot-pounds) with a Torque Wrench. Take the car off the jack stands and take for a drive.
A quiet differential is a happy differential. Hope this service tip has helped. Thanks for reading!