Duramax Rear Differential 12,000 on fluid/25,000 total miles

wwillson

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This is a 50/50 mix of SuperTech 75w-90/75w-140 run for 12,000 miles mostly pulling the truck has a total of 25,000 miles.

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I'm not used to looking at UOA for Rear Differentials. But that FE seems really high to me? Am I wrong? Was the Lubricant very discolored? Its been 20,000 miles plus for my Duramax now. I was thinking next summer to get it done. Did you use OEM Lube or something else?
 
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Kestas

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The teeth of hypoid gears experience more sliding wear than many other gear designs. I would expect Fe content to be high.
 
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Originally Posted by wwillson
This is a 50/50 mix of SuperTech 75w-90/75w-140 run for 12,000 miles mostly pulling the truck has a total of 25,000 miles.
Are you staying with 12k OCI or extending further?
 
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I'm all in on the early drain and fill. What do you plan on for the next drain fill? Meaning mileage? I did my F150 at 25k and will do it again at 100k. Just wondering what you plan. I also did my Subaru at 30k and will do again at 100k. And then again at 200k and then never again til she is put down.
 

wwillson

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Biscut, I will probably go to 25,000 for the next interval. Does anyone know what GM recommends? I can't find it in my manuals.
 
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A quality 75W90 (we use Chevron Delo stuff) will easily go 500,000 miles in a AAM or Dana rear axle on a GM. We do it, and have had ZERO failures. We dump the factory oil at the first service (usually around 10k miles) it's usually kinda nasty, and put in the Chevron and forget about it.
 
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I was always recommended M1 75W90 in my gm's. I used RP Max-Gear 75W90 in my Express 2500HD van. That diff was smooth as butter along with being as quiet as a mouse. I realized the highest fuel economy with RP products also.
 
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Originally Posted by JohnnyJohnson
I'm not used to looking at UOA for Rear Differentials. But that FE seems really high to me? Am I wrong?
No, it is not high. My 2015 F250 had 339PPM of FE with only 8,600 miles on the first OC. The vast majority of axle wear occurs in the first 15,000 miles or so and despite longer and longer runs the wear metals will continue to drop.
 
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Originally Posted by wwillson
Biscut, I will probably go to 25,000 for the next interval. Does anyone know what GM recommends? I can't find it in my manuals.
You won't like this Dubya. From the 2018 Duramax Supplemental manual it does not suggest a differential oil change, at least not in the first 150,000 miles. Same for the 2020 Silverado manual. From my 2008 owners manual on my 3/4 ton Chev, it does not suggest differential fluid change as well. I did one at 100,000 miles using AC Delco 75W90 Synthetic and another at 175,000 miles using Motomaster 75w90 Synthetic. It runs perfectly with 180,000 miles on it. For the transfer case it suggests 50,000 miles but I do it every two years. It's as easy as an oil change. YRMV. smile
 
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4WD

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Same here … AAM builds the axle and there is nothing in my manuals … Just thinking 50k still works after an early change
 
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I find that GM under fills their differentials in my opinion. I like about 1.5 inches below the fill hole. I'm slowly switching everything to 80W140 Chevron & Petro-Canada.
 
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Originally Posted by userfriendly
I find that GM under fills their differentials in my opinion. I like about 1.5 inches below the fill hole. I'm slowly switching everything to 80W140 Chevron & Petro-Canada.
Spec is 17-21 mm (0.6-0.8 inches) below fill hole.

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wwillson

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Originally Posted by PiperOne
A quality 75W90 (we use Chevron Delo stuff) will easily go 500,000 miles in a AAM or Dana rear axle on a GM. We do it, and have had ZERO failures. We dump the factory oil at the first service (usually around 10k miles) it's usually kinda nasty, and put in the Chevron and forget about it.
Wow - I guess I'm over maintaining by a wide margin? Any chance you have a UOA in your fluid after 500,000 miles?
 
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No oil analysis on the rear ends. If they are quiet and don't clunk we leave them be. Gear oils have gotten sooo much better over the years as well as the metallurgy in the rear ends we just don't have issues. Class 8 highway trucks (semi) are all over 500,000 mile drains and warranty approved at that interval.
 

dnewton3

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The AAM 11.5 is very reliable and not picky about brand or grade. Needs a bit of FM for the clutch pack if G-80 equipped, which this one is. Diff fluids see far more Fe than others samples like engines. This one is perfectly fine. Nothing but expected normal wear here. As for the OCI, one or two drain/fill cycles are all that is needed and then 100k miles thereafter if using any decent syn GL-5. No need or benefit to overly frequent changes, as they won't alter the wear rates. Jim Allen told me in an off-line conversation that diff gear wear is about 99% attributed to gear/pinion set up. As long as that is good then it's fine and no amount of OCIs will affect the wear rate once the diff is broken in. Further, when I had my Dmax, he told me the AAM 11.5 runs fairly cool for a rear diff and that fluid overheating even when towing is essentially an overblown concern. He was clearly right because I added cooling fins to my diff cover and didn't see any appreciable changes in wear. Diff wear is what it is; it won't change a whole lot after break-in. Wayne you can run this next load WAY further. I would not OCI again until 100k. Just pull the fill plug every 25k and check the fluid level and only top off if needed. NOTE: for those whom are unaware, Jim Allen is a noted published automotive tech writer. He penned a book about differentials with Randy (of Randy's ring and pinion fame). Jim has forgotten more about diffs than most of us would ever know.
 
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Haha gone are the days when you could fill the case to the bottom of the hole and be confident that the level is right. I don't know why every little thing has to get more complicated when it has been working fine for decades.
 
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