Eaton's Recommendations on Locking Rear Diff Service

[DmaxMaverick]

Your level is OK. The later models had the service lube amount adjusted to reduce incidents of axle seal leakage. It was 3.8L, and is now about 3L, or about 3/4" below the fill hole. Anywhere between 1/2" and 1" is fine.

The goo you found (and hopefully cleaned) on the drain plug and the color is normal for a first/early service. It's all the fine wear-in metal particles.

[MacDR50]

Thanks DM. I will be looking at the front end, most likely before the winter.

[DmaxMaverick]

Good deal. The front end is often neglected (out of sight, out of mind). 2 qts. for that one. You can use the same lube as the rear, but any good synthetic GL-5 75-90 will do as well (for a LOT less $$).

[SoTxPollock]

How about an update, I now have 191,000 miles on the odometer, all on Mobil 1 differential oil full synthetic. The first 100,000 was 75-90, the last time I changed it I couldn't find enough of the 75-90 and had to mix in some 75-140 for the rear. I calculated the average based on the number of ounces of each and it averaged out to be 75-120. Just got back from towing very heavy, 15,500 5er, with truck weighting in at around 8,000lbs. Trip was 14,138 miles. Absolutely zero problems with the truck, except for the busted upper u-joint boots from those lousy Yukon washed out roads. I think I can safely say that Mobil 1 gear lube is a good as any, based on my driving. I'm still amazed that the rear gears could take the punishment of decending into Death Valley for so long a time geared down with all that weight pushing downhill. I wish I could have had a pyrometer on the rear differential to know just how hot it got. She's still rolling along as silent as ever. That being said, I just have to think that any full synthetic gear oil that meets GM specs would have done just as well. Yikes I just realized, I've run slightly over 100,000 miles already on the Mobil 1 Automatic Transmission fluid already. Time to go shopping for some fluids for Christmas and get some fresh fluids in the ole truck, we go a lot of miles to go yet and I'm looking forward to every one of them. Thank God for those evil Big Oil People who know how to make that stuff that good. Oh and by the way if you look around you no matter where you are, If its manufactured and you're looking at it. Thank Big Oil Corporations, that's where it all comes from, do the research, it will amaze you. I photographed a wall in a conference room at The Artic Caribou Inn in Prudhoe Bay and the list of items made from Oil and Natural Gas by those Evil Oil Corporations is so extensive it cover all 4 sides of the room which would seat about a hundred people, a fair size room the list runs from floor to celing all around the room and I could think of a lot more new items that wern't even around when they made that list. When I watch Our President attacking the Big Evil Oil Corporations like he has it just turns me off. How could so much ignorance rise to the top like that? It's difficult to understand. Everytime I fuel up I think about how we all just take it for granted that everything is just the way we want it to be for our trucks. How blessed we are that good people all over this planet have what it takes to explore, drill, accumulate, ship and produce everything we need, where ever we go. Sorry for the ..... No I'm not.......... it needed to be said and I said it. Travel on Diesel burners, we still have the most BTU's per gallon of affordable fuel available everywhere, and the outstanding lubricants that keep um rollin.

[More Power]

The early trucks were equipped with convention petroleum lube in the front axle. But, apparently some 4x4 trucks had problems with their front axle when driven in cold environments. This caused a change in lube recommendations for later trucks. And, GM produced a service bulletin for the older trucks, which allows them to use synthetic lube (once a specific part is swapped for one that is compatible with synthetic).

Bulletin No.: 03-04-19-001B, Date: September, 2004

Use Synthetic Axle Lubricant, P/N 12378261 or P/N 89021677 (Canadian P/N 10953455 or P/N 89021678). Each of these part numbers is the same axle lubricant, with differences in packaging only. Fill to a level between 6 and 9 mm (0.25 in to 0.375 in) below the bottom of the fill plug.

If the vent hose connector is black in color, it will need to be changed so that the 0-ring seal is compatible with the synthetic lubricant. Install vent connector, P/N 12479390. Follow the Front Drive Axle Vent Hose Connector Replacement procedure in the Service Manual.