I have searched the owner's manual and cannot find any reference to the fluid change frequency. The only reference I have found is to the type of gear lube to use. Many posts on this great forum say I should have changed it a long time ago with any of a wide variety of fluids from "grape juice" to Mobil 1, to Amzoil. If there is an advantage to changing, such as making the axle last longer, I'd think that GM would want the same thing for warranty purposes. Please straighten me out on this, since I'm obviously confused. If it makes a difference, I have 25K on the clock and have towed an 11K trailer for about 8k of those.

2004 Silverado D/A 3500 DRW LT

Can't say I've found anything myself so I'm just going to do it every 2 years. I have 46k on it now and wish I'd have done it sooner but........ It is getting done this weekend. Have 6 quartz of Mobil 1 sitting in the garage that was picked up tonight. Going in both axles this weekend. Hope that helps.

To add to the confusion, I checked the Maintenance and Lubrication section of the Factory Service Manual set I bought from Helms. On page 0-58, there is a heading of DRIVE AXLE SERVICE. It says, "Change the axle fluid according to the maintenance schedule interfals. For the maintenance schedule refer to Scheduled Maintenance on page 0-51." By turning to page 0-51, you will find NO mention of the drive axle, nor will you find any mention of the drive axle on page 0-52. Why would they tell us to change according to a schedule and not tell us what the schedule is? More confused than ever, now! That info must be :secret:

"grape juice" to Mobil 1, to Amzoil

Is there something to look for in the oil grade like GL-5. Is the GL-5 the only thing to look for?

If you do a search on "grape", you will find a lot of members that are changing their diff fluids as early as 500 miles. You will also find a lot of discussion on what to use. Some say use only the OEM fluid (Grape Juice at over $20/qt) while others say use Mobil 1 or other brands 75-90 or 80-140 if towing. Mass confusion. That's why I went to the Owner's Manual and Factory Service Manual to clarify, not only fluid type but also required change intevals. Other than specifying the OEM fluid (no surprise there,) and the one short blurb in the FSM saying to change it according to the schedule they don't give:eek:, both are silent on the issue. I went to Eaton's site and found all kinds of info on the diff, including a neat little video showing how it works, but no info on fluid type or service interval. Still confused?

I don't think there are really any hard rules about when to change. The differential is pretty tough and I think you would have to work pretty hard to hurt it. That being said, I changed mine using Amsoil synthetic at 500 miles, then again at around 5000 or so. Haven't touched it (except to check level occasionally) since and I now have 35,000 miles.

Talked to the local dealer today. Service writer says they recommend a change at 30K. Waiting for a response from Eaton, also.

According to my dealer, up through 2004 they (GM) recomended changing the rear diff fluid at 500 miles if you were going to do any towing.
Starting with 2005 that recomendation was dropped by GM but the dealer knows of no reason why. His speculation (and it is speculation) is that GM dropped that requirement due to complaints about the cost of the fluid change at 500 miles. about $100 for fluid and labor. (most of it was the fluid).

They do lot's of diesel service and really know their stuff so I trust their judgement.

The dealer still recomend changing at between 500 and 2000 miles or so, then every xxK miles. (I don't remember the mileage) if you have the locking differential.

If that was a GM recommendation from that far back, I wonder why they didn'tn put it in the owners' manual? When I had mine in to the dealer for it's first oil change at about 5,000 miles, I asked if there was any other service needed. "Nope, your good to go until the DIC says come back! Just follow the schedule in the owners manual for the rest." I think there must be a lot of confusion all around.

I know it is written somewhere by factory that it is recommended to change the rear differential fluid after 500 miles of towing.

I know it is written somewhere by factory that it is recommended to change the rear differential fluid after 500 miles of towing.

That recommendation was dropped in the 2003 owners manuals.

American Axle Manufacturing built the rear differential and it is their recommendation to change it after 500 towing miles. They set it up with tight tolerances which builds heat. I changed mine at 2400. It had a lot of small shavings and a lot of dust particles from the clutch discs. I changed it again at around 30K. It looked like I just put it in. Later! Frank

I did my first change at 1,400 miles with Mobil 1 75w-90. Did my second change 9 months later with Mobil 1 75w-90 at 24,000. Mine sure didn't look like it was new. I will change mine every 20,000.

Daily stop and go and highway driving. Occasional 10,000 pound trailer towing.

I changed by rear diff yesterday after reading the info on these forums. I've got a 2002 Dually and tow. The fluid was a full quart low and was black. The magnetic drain plug had a lot of metal sludge on it and one large (half the diameter of a dime) sized piece of shaved metal.

Replaced fluid with Valvoline 75W90 Extreme synthetic fluid (on sale yesterday at NAPA for $6.99/qt.) Used 4 qts to refill. Plan to run this fluid for a few thousand miles then drain and refill with Amsoil 80W140 Severe Gear Oil - synthetic of course.

Will be changing the front diff today after I replace the black vacuum plug with the new white nylon one - used for synthetic fluids.

I changed my rear end fluid at 26k miles (Bought used). Black and stinky. Not much shavings however. Will replace again in 10k to insure everything is clean.

Front was a different story - got a 1/2" long "worm" of shavings attached to the drain plug. Oil was tinted but not black. Definately don't forgot to do the front!