Low Quantity (1 quart) in Differential

DIff oil doesn't "burn" off, so if it didn't leak out, it means it was never topped off. Just an FYI, anytime an axle is assembled, the oil won't reach the hubs (on a full float) until after several turns are made at speed. Oil is forced into the hubs only by gravity, which is why new trucks come low from the factory. If I pull an axle apart, I give it a full day for the oil to settle in before topping it off (note: you also can't drain all the oil out unless you pull the hubs... so a regular drain and fill doesn't require this).

Thanks for the replies. I have filled the diff till about 1/2 inch below the hole. I will buy another quart of fluid and monitor the level more closely. But getting under there and checking is a major hassle when your 67.
Thanks again
Bill

Have you changed the fluid in the diff before? The rear diff takes about 3.5 quarts for a fluid change.

Only use a GL5 grade synthetic fluid in the front and rear diff. Limited slip additive is not needed.


I changed mine after 600 miles of towing and when I added a PML diff cover.

All the GM diffs come from the factory "low" on level.

From my owners manual (was the same for my previous 2005 D/A).

For all 6.6 L Duramax Diesel 2500HD Series applications and all 3500 Series applications, the proper level is from 17mm to 21mm (0.6 in to 0.8 in) below the bottom of the fill plug hole, located on the rear axle. Add only enough fluid to reach the proper level.

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Liquids will expand and too much can lead to foaming, churning of the lube and pressure build up resulting in blown seals.

I have filled the rear diff until it starts to seep out of the fill plug and it did not create any problems. This would be over-filling per GMs standards.

first, no i don't think you hurt anything. Second our trucks are as smketter said are 1/2 below the hole. I am not sure how you are supposed to measure such a thing but i lay my last knuckle of my little finger in the hole and bend it down...it comes out about half covered in oil. others are filling level with the hole...which likely doesn't hurt anything either.

Either way make sure the stuck is sitting level. it will make more difference than you think.

How full is full? I thought GM fill was ~1/2" below the plug hole.