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Discussion Starter · #1 ·
Changed the fluid in the rear differential. The amount of fluid that I removed was ~2.25 quarts, and the fluid I put back in was ~3.25 quarts. I put fluid in until it ran out the fill plug. I wonder why the difference?

Used Mobil 1 75W-90 gear oil.
 

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Changed the fluid in the rear differential. The amount of fluid that I removed was ~2.25 quarts, and the fluid I put back in was ~3.25 quarts. I put fluid in until it ran out the fill plug. I wonder why the difference?

Used Mobil 1 75W-90 gear oil.
the 10.5 takes 3.25QT / 9.5 2.7QT .. now on filling with the vehicle LEVEL in warm weather fill to just below the fill hole. in cold weather fill to 1/2in below the fill hole. this fluid when hot expands.

since you drained out A QT less then you must have a leak. check the fluid every oil change for level and fluid color.
 

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since you drained out A QT less then you must have a leak. check the fluid every oil change for level and fluid color.

Could be as simple as the position of the asymmetrical center section...turn it one way and it will displace more volume than if its turned 90*. Depending on its position when it was last filled...

A leak on a differential should show up pretty readily. Even an ounce will make a complete mess underneath a truck; let alone a quart.
 

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Could be as simple as the position of the asymmetrical center section...turn it one way and it will displace more volume than if its turned 90*. Depending on its position when it was last filled...

A leak on a differential should show up pretty readily. Even an ounce will make a complete mess underneath a truck; let alone a quart.
there is a vent tube hose if it got very the fluid may have come out of it as another possible cause or maybe it was never filled to the proper level this can occur if the vehicle was not on level surface.
 

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I want to say mine was "low" by my standards when I brought it home...it was around a 1/2 inch (or more) below the fill hole. I'm thinking they probably fill them by volume (automated, so to speak), and not by level...I fill this one to where the fluid runs out the fill hole.
 

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Discussion Starter · #6 ·
the 10.5 takes 3.25QT / 9.5 2.7QT .. now on filling with the vehicle LEVEL in warm weather fill to just below the fill hole. in cold weather fill to 1/2in below the fill hole. this fluid when hot expands.

since you drained out A QT less then you must have a leak. check the fluid every oil change for level and fluid color.
My truck has the 8.6" ring gear. I have your standard 10 bolt G80 locking diff. There are no leaks on the axles, pinion or other areas. The truck is a 2013

After reading a BUNCH of posts on other forums I gather the capacity of that particular diff is ~2.5 quarts. Many have said that the proper fill level is 0.5" below the fill plug.

I filled the diff up until it came running out of the fill plug and waited for it to stop running out. Is this improper, I don't know, I've always filled gearboxes up until the fluid came running out of the fill plug.
 

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I have a 10.5", and I want to remember the 10.5" is "level with the fill hole"; but I do know it depends on the differential.
 

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Discussion Starter · #8 ·
I have a 10.5", and I want to remember the 10.5" is "level with the fill hole"; but I do know it depends on the differential.
You must have a 2500 Silverado.

I was under the impression that the 2500 and 3500 rear differentials were made by Dana while the 1500 diffs were made by Eaton.
 

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You must have a 2500 Silverado.

I was under the impression that the 2500 and 3500 rear differentials were made by Dana while the 1500 diffs were made by Eaton.

The only Dana I know that GM used in a rear application was the Dana 60 in some of the 3/4 ton vans a while back. Until they switched to IFS, they used the D44 (later replaced by the Corp 10-bolt) and D60 for the front axle.

This 10.5 is what i know as a "Corporate 14-bolt", and its design has been in use by GM since the late 60s/early 70s.
 

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Discussion Starter · #10 ·
Before this thread gets too far off topic:

I would like the opinion of some of the forum members as do they think that filling G80 8.6" differential on a 2013 SIlverado up to the fill plug is bad, good, does not matter?

Thanks.
 

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Before this thread gets too far off topic:

I would like the opinion of some of the forum members as do they think that filling G80 8.6" differential on a 2013 SIlverado up to the fill plug is bad, good, does not matter?

Thanks.

The only thing I could see happening is if it was overfull it would aerate and foam...

However, the way a differential lubrication system works is that the ring gear slings the lubricant up into the front of the housing to flood the pinion bearings. So if its a little over filled, its not going to know the difference (think about running on a side hill, up or down a steep hill, etc...the level is always changing anyway.
 

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Before this thread gets too far off topic:

I would like the opinion of some of the forum members as do they think that filling G80 8.6" differential on a 2013 SIlverado up to the fill plug is bad, good, does not matter?

Thanks.
I never seen a diff go bad from too much fluid. some say the seals could get damaged from pressure build up.

I know that if the vehicle is not level you can put 4.5 QTS in it . or put in 1 qt too little. if the front end is high you can overfill very easy.
 

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Discussion Starter · #13 ·
I never seen a diff go bad from too much fluid. some say the seals could get damaged from pressure build up.

I know that if the vehicle is not level you can put 4.5 QTS in it . or put in 1 qt too little. if the front end is high you can overfill very easy.
I was under the impression that differentials have some kind of venting system on them so too much pressure cannot happen.
 

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Yes, the venting would prevent pressure buildup.

FWIW, I ran the 11.50AAM in my Dodge (same thing under a Duramax) with an ORU cover that placed the fill port 1.5 inches higher...I ran with the fluid that much high, in an 85w140 blend for 150k miles, then switched to a 75w140 for another 50k. I never had a dribble.

The AAMs are a very good axle...
 

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I was under the impression that differentials have some kind of venting system on them so too much pressure cannot happen.
the venting hose can over time get plugged up. when I had my frame crossmember replaced they crushed this hose / did not route it properly. I caught this the next day when I dropped the fuel tank and rustproofed the frame and the crossmembers. even with the diff being properly filled had I not caught this I would have had seal damage/leaks. this fluid expands alot when heating under use.

my front diff was factory filled too high and it was coming out the over flow .
 

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I allways fill them til they drip out, never had a prob. Also rear ends get pretty toasty and the vent tube is important. Ever notice a salt truck covered in slush but the pumpkin is bone dry?
 

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I have not been able to find the correct volume of fluid; however, the level should be between 1/2" below the hole, to the bottom of the hole (truck level).
In other words, if checking and the level is no lower than 1/2" below the hole, the level is good. If filling, or topping up, the fluid should be added until it drips out of the fill hole.
 

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I have not been able to find the correct volume of fluid; however, the level should be between 1/2" below the hole, to the bottom of the hole (truck level).
In other words, if checking and the level is no lower than 1/2" below the hole, the level is good. If filling, or topping up, the fluid should be added until it drips out of the fill hole.
From the 2012 OM:

To get an accurate reading, the
vehicle should be on a level
surface.

For all 4.3 L, 4.8 L and 5.3 L
1500 Series applications, the
proper level is 1.0mm to
19.0mm (0.04 in to 0.7 in)
below the bottom of the fill hole,
located on the rear axle.
Add only enough fluid to reach
the proper level.

For all 6.0 L and 6.2 L
1500 Series applications, the
proper level is from 15mm to
40mm (0.6 in to 1.6 in) below
the bottom of the fill plug hole,
located on the rear axle.
Add only enough fluid to reach
the proper level.

For all 6.0 L 2500HD Series
applications, the proper level is
from 0mm to 13mm (0 to 0.5 in)
below the bottom of the fill plug
hole, located on the rear axle.
Add only enough fluid to reach
the proper level.

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.


Interesting enough:

All axle assemblies are filled by
volume of fluid during production.
They are not filled to reach a certain
level. When checking the fluid level
on any axle, variations in the
readings can be caused by factory
fill differences between the minimum
and the maximum fluid volume.
 

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Discussion Starter · #19 ·
So all in all it sounds like just fill the diff until it comes running out the fill hole.
 
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