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Discussion Starter · #1 ·
I changed the gear oil in the rear diff today. When I opened the fill port, I discovered the lube level was 5/8 of an inch below the bottom of the fill port. This is a new truck with only 4000 miles on it so clearly wasn't filled properly from the factory. And no, I have no leaks.

I'm just hopeful that the pinion bearing or the wheel bearings didn't starve for oil with it that low.

If you have a newer truck, you may want to check all your fluids to make sure they are up to snuff. Also, if you haven't greased your grease points on the front end, they are dry from the factory too.
 

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I don't know whether 2020+ trucks have a different axle or require different fluid fill levels, but on 2019 and prior trucks, the rear differential is supposed to be filled below the fill port. The manual on my 2017 and 2009 both specify that the fluid should be 0.6 to 0.8 inches below the fill port.
 

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Discussion Starter · #3 · (Edited)
consumedbywater, I believe you are correct. FWIW, I wrote to AAM to see what they say. There is a good chance they won't respond, but we will see.

My service manual is mute on this topic.
 

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From my 2014 manual.

For all 6.6L Duramax Diesel 2500HD Series applications and all 3500 Series applications, the proper level is from 17 mm to 21 mm (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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Our 2016 was low in the rear end, below the recommended fill level and the tranny needed a full quart. Always good to check.
 

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2017, 2500HD, LTZ, front guard, Duraflap mudguards, Leer bed topper
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2017.. replaced the front and rear diff and transfer case lube.. low in each.. and front looked like chocolate milk..
 

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19 Denali L5P SOTF Tuned. PLUS lots more
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2017.. replaced the front and rear diff and transfer case lube.. low in each.. and front looked like chocolate milk..
How much do you use your 4wheel drive? Got me nervous wanting to check mine now. Did you have a glitter shard party on your magnet in the transfer case? I love me some chocolate milk. Just not in my trucks components.
 

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2017, 2500HD, LTZ, front guard, Duraflap mudguards, Leer bed topper
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How much do you use your 4wheel drive? Got me nervous wanting to check mine now. Did you have a glitter shard party on your magnet in the transfer case? I love me some chocolate milk. Just not in my trucks components.
I do NOT use the 4x4 .. very rarely. Once about 48K I left it in 4HI for about 200 miles.. but not over 65MPH. Should not cause any issue... At 50k I just decided to change. It all dumped into the same bucket and was last I pulled. There were only normal sludge type pieces on the case plug.

I checked it a few weeks ago by briefly removing the plug.. and it was clean as when I refilled and nothing on the magnet. Everyone I spoke to thinks it was maybe some water... and we had only driven through severly heavy rain a few times... never deep water ...
 

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2017.. replaced the front and rear diff and transfer case lube.. low in each.. and front looked like chocolate milk..
Most likely from condensation. If you rarely use 4wd, the fluid never gets hot enough to burn the moisture out. I wouldn’t be overly concerned if it was mine. Maybe try and put it in 4hi once a month and drive for a few miles, get the fluid hot. I try to remember to do that on all our 4wd vehicles.
 

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Most likely from condensation. If you rarely use 4wd, the fluid never gets hot enough to burn the moisture out. I wouldn’t be overly concerned if it was mine. Maybe try and put it in 4hi once a month and drive for a few miles, get the fluid hot. I try to remember to do that on all our 4wd vehicles.

Great explanation. I rarely use mine as well. I've drove my 19 steady and hard for 85k with 3k lbs in the bed. Holding up amazing. I meticulously maintain. I have a 16 model still with 37's and 115k miles. Use it for rough jobs and wetland jobs. Never been checked except for the engine oil. Rear pinion started leaking 110k and replaced. Oil looked great then. I admit to lots of negligence on it and I send it full blast through the mud to not get stuck. I feel as if I would let my gm constituents down for not testing her like a rock if I started checking fluids and babying her. She's ricocheted off a telephone, been part time employee drove also, and the air dam left the unit around 4k from being drug through the mud. Still going strong with original batteries
 

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I changed the gear oil in the rear diff today. When I opened the fill port, I discovered the lube level was 5/8 of an inch below the bottom of the fill port. This is a new truck with only 4000 miles on it so clearly wasn't filled properly from the factory. And no, I have no leaks.

I'm just hopeful that the pinion bearing or the wheel bearings didn't starve for oil with it that low.

If you have a newer truck, you may want to check all your fluids to make sure they are up to snuff. Also, if you haven't greased your grease points on the front end, they are dry from the factory too.
There is a lot more going on behind the cover than you think. The level and shape of cover control the fluid mechanics of lubrication and changing the level or the cover can really screw up the lubrication to the bearings etc. If you do a search on youtube about Banks Engineering testing diff covers you will be shocked. The so called performance aftermarket ones are junk and will ruin you diff in not time.
 

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The newer fords have assembly lube in their front diffs that make it look milky I wouldn't be surprised if gm does the same thing these days. I would change it also but thats just me I'm just saying it may be factory. Not sure yet haven't gotten many newer chevys at work yet
 

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The newer fords have assembly lube in their front diffs that make it look milky I wouldn't be surprised if gm does the same thing these days. I would change it also but thats just me I'm just saying it may be factory. Not sure yet haven't gotten many newer chevys at work yet
Never heard of assembly lube, normally they put the normal lube in. It goes through a high heat cycle the first 100-200 miles when the bearings are new and then it stabilizes for life.
 

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Google ford front diff fluid milky I had to I thought it was water but after some research I was learned lol I couldn't sell something to someone that they didn't need I know some shops would but I always thought it's better to know
 
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