2004-2006 Pontiac GTO Differential Service

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.

2004-2006 Pontiac GTO Rear Drive Axle Section Of The Service Manual
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 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?

Detroit Truetrac units perform best when using GL5 rated mineral / petroleum based gear oil. Synthetic lubes are discouraged. Do NOT use friction modifier additives or lubes formulated with friction modifiers. See the “Lubrication” section of the product manual for further details and specifications. 
 

Step 2:
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.

 

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

GTO 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.

 

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 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!

6 Comments

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  1. QQ: How many miles between differential changes ?

    Thank you,

    Rob

    1. Hi Rob and thanks for your question.

      Your question even had me searching for an answer. Doesn’t seem to be a recommended mileage in the service manual when to change the differential fluid. This is just in my opinion, you should probably change the fluid at the 50K thousand mile mark. Its not hard to do, and the rear ends on these cars are kind of touchy. I have seen posts on various blogs and forums where owners have destroyed the rear end in 20k thousand miles, and I have seen others who have never changed the fluid and still have zero issues of differential noise.

      The Torco RGO replacement differential fluid by far is better than the stock General Motors fluid. It will quiet up the rear end from gear noise. Any kind of rear end grinding or clunking noise from the differential is never a good thing. Unless of course you changed the gears to the 3:90 or 4:10 ring and pinion, in which case some gear noise is expected. But the noise made from these gears is more of a “whine” rather than a clunk or grind, which is perfectly normal.

      Thanks for the question and I hope this helps.

  2. Mark, my 2004 GTO has 157K miles (it’s my daily driver, purchased new). The car is mostly stock, equipped with the 4L60E automatic, which was rebuilt at 100,000 miles. I’ve changed the driveshaft center carrier bearings and both flex couplings. the differential oil was changed at 125K miles but I don’t know what type of fluid was used, and I know that a friction modifier was not added. I get the clunking noise; it appears after the car has been driven for about 10 minutes. I hear and feel it just before the car comes to a full stop, when the transmission is downshifting, and when I start accelerating slowly. Rapid acceleration produces no clunk, the transmission upshifts through the gears smoothly, and the car is stable at very high speeds (I.e 125 mph bursts on the highway). It seems to me that I need to do what you recommend with the Torco products. Agree? Any other thoughts. Thanks!

    1. Completely agree. I would just take a day to change out the differential fluid. You have a stock differential, so you will need some Friction Modifier. Here’s where I get mine.
      Torco RGO: RGO
      Torco Type F Friction Modifier: Friction Modifier

      You will be happier.

  3. Thanks Mark. I have ordered the products and will let you know how I made out.

    1. Wise choice my friend, LOL. I threw out the “FR Sports” links because they seem to have the best price, and they ship pretty fast as well. Never had a single problem ordering from there.

      Just be careful putting the gear oil in. Stuff is extremely thick! Use an old gear oil container that has a pour tip on it, or buy an adapter to screw on the top of the RGO oil, or you could try a handpump……which I have never heard anyone having any luck using a pump. Pump will break before you get half a quart in.

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