CHECK YOUR DIFFS...

[the8rotor]

3 minutes ago, Kerry Pulaski said:

She was level on jack stands. Let it drip out to a pan till it stopped.  Merely a table spoon dripped out, then capped tight.

As the spec. does say to -0- at fill hole, that is max fill level value.

I even had the Qt's of 75w-90 in hot sink water for 15 min. to make it easy to flow. If cold and stiff, then could force an overfill before capping the fill plug.

I work on industrial machines for over 43 years. These use precision planetary gearboxes. Oil viscosity and levels are critical.

I expected the same care and precision with my GMC dealer........I hate teaching a supplier of high tech product.

 

Completely ridiculous these dealerships don't even bother checking even when you tipped them off to check. 

[Kerry Pulaski]

On 12/13/2023 at 8:34 PM, BuckWallace said:

Took my truck to the dealer today for my oil free change and asked them to top off the diff fluid as well. They confirmed it was low, filled it up, and got it all documented. I don't suspect this will cause any long-term issues, but at least I have the paperwork.

Must document a paper trail for any product warranty issue. Learned that long ago on machinery and parts I sell.

Those that heavy tow, and did not catch this low diff. fluid in a timely manner, I would document & save any metal filings if the fill plug has a magnetic insert, and save the fluid for analysis, if questionable.

 

My '24 Duramax 6.6 at 2500 mi. the oil on the dipstick was very very black. Perhaps due to break-in oil ?  At 4500 mi. did first oil change and had them save the GM filter with captured oil in it. Have it a sealed Tupperware container to send out for analysis, after reading about some recent Duramax issues, should they arise.

[Rick_]

My rear axle was at 1 1/4" low at 5500 miles.  Good thing I towed with it right out of the gate. 

I pulled the cover off, cleaned it up, put it back together and filled it with 4qts Amsoil Severe Service 75w-90.

If you drop the spare, there is a ton of room to use a bendy funnel tube to add fluid.

With what little foreign matter was in there, I'm not worried about longevity. 

[dal1980]

My 2024 2500HD Silverado Gasser took about 2/3 of a quart, checked at 150 miles.

My brothers 2024 Denali HD (2500) Dmax with max tow, 3500 rear axle took over a quart.  

My neighbors were looking at me like I was nuts crawling under a 3 day old truck with bottles of gear oil and a grease gun.

[64BAwagon]

The spec is .4 inches or 10 mm below fill hole. I posted it on here a few months ago. 

[Pryme]

10 hours ago, dal1980 said:

My 2024 2500HD Silverado Gasser took about 2/3 of a quart, checked at 150 miles.

My brothers 2024 Denali HD (2500) Dmax with max tow, 3500 rear axle took over a quart.  

My neighbors were looking at me like I was nuts crawling under a 3 day old truck with bottles of gear oil and a grease gun.

Mine too I was under mine when it had less than 100 miles to “look around” ha

 

non car/truck guys wouldn’t understand 

[64BAwagon]

Nothing like spending North of 60K on a truck only to crawl around under it in the first couple of weeks. 

Mine got almost a qt of diff fluid in the rear and 3 pumps of grease in all the fittings plus almost 2 gallons of Fluid film in every conceivable dark place. 

 

GM was made aware of the diffs being low. I dont know if any action was taken. This is controlled by American axle and GM does not add or check the fluid during or after assembly of the truck. I was told that AA fills by "weight" and not by volume which really makes no sense since many here have reported lower levels than the GM spec. 

My front diff was at the correct level and I havent heard anyone report that their front was low. 

 

Scott

Edited December 28, 2023 by 64BAwagon

[gemarsh]

24 minutes ago, 64BAwagon said:

...

My front diff was at the correct level and I havent heard anyone report that their front was low. 

 

Scott

 

 

The OP's first post on this thread, said his front axle was a half a quart low.

[ssgballistics]

Changed my rear diff fluid this morning (7200 miles on truck). Rear diff was about a qt low (couldn’t even reach the fluid with my pinky) when I had checked it at around 1000 miles. I added a full quart to bring it to the correct level (still not running out, approximately 1/8” below plug). This morning took the cover off, cleaned everything up, and added 4 qts to bring the fluid to level with the plug. The specified capacity of 3.15-3.17 qts seems insufficient. 

[64BAwagon]

1 hour ago, gemarsh said:

 

 

The OP's first post on this thread, said his front axle was a half a quart low.

You got me, long thread, short memory LOL Does it help if I tell folks no one asks me for proof if I order a senior coffee at Mc D's ? 

Edited December 28, 2023 by 64BAwagon

[SoCal Angler]

Great threads never die!

 

My '23 does not have a drain plug.

I'll be checking the level in the next few days.  

 

A few questions that I do not believe were addressed....

 

1.  If low, is adding the AC Delco 75W-90 the preferred oil to bring fill level to within 0"-.4", so as not to mix oils...assuming GM used the same oil that it sells at retail?  Since 0" is within the specs, is adding oil until it flows out of fill hole an acceptable level?

 

2.  Is the '23 3500 GAS 4x4 HD axle a LS rear axle or something else?  My window sticker says, "auto locking rear differential." If this means that it is not a LS axle...would the added modifiers be a concern when using Amsoil?  I see Amsoil makes a Long LiFe 100% Synthetic Gear oil 75W-90 without modifiers...is this one preferred?

 

3. What are the model #s for the ('23 3500HD Gas models, 4x4) rear axle, front axle, and transfer case?  Are model #s stamped onto axles and transfer case, if so where?  I can only find ON GMC website that it is an 11.5" ring gear axle.

 

4.  Since owner's manual does not provide any gear oil specs (type/qty) for front/rear/transfer case, where can official info be located?

 

5.  Unable to find a part number for the fill plug gasket.  Anyone have the part #?

 

NOTE:  I also found these discussions interesting...wonder if this is the same/similar axle and would it apply to our current axles?

 

Locking Diff Lubricants

 

Oil Level and Fill Plug gasket

 

 

Thanks!

Edited February 9 by SoCal Angler

[Pryme]

2 hours ago, SoCal Angler said:

Great threads never die!

 

My '23 does not have a drain plug.

I'll be checking the level in the next few days.  

 

A few questions that I do not believe were addressed....

 

1.  If low, is adding the AC Delco 75W-90 the preferred oil to bring fill level to within 0"-.4", so as not to mix oils...assuming GM used the same oil that it sells at retail?  Since 0" is within the specs, is adding oil until it flows out of fill hole an acceptable level?

 

2.  Is the '23 3500 GAS 4x4 HD axle a LS rear axle or something else?  My window sticker says, "auto locking rear differential." If this means that it is not a LS axle...would the added modifiers be a concern when using Amsoil?  I see Amsoil makes a Long LiFe 100% Synthetic Gear oil 75W-90 without modifiers...is this one preferred?

 

3. What are the model #s for the ('23 3500HD Gas models, 4x4) rear axle, front axle, and transfer case?  Are model #s stamped onto axles and transfer case, if so where?  I can only find ON GMC website that it is an 11.5" ring gear axle.

 

4.  Since owner's manual does not provide any gear oil specs (type/qty) for front/rear/transfer case, where can official info be located?

 

5.  Unable to find a part number for the fill plug gasket.  Anyone have the part #?

 

NOTE:  I also found these discussions interesting...wonder if this is the same/similar axle and would it apply to our current axles?

 

Locking Diff Lubricants

 

Oil Level and Fill Plug gasket

 

 

Thanks!

1. Yes

2. it’s a G80 mechanical locker that locks when wheel slip is sensed. Been using it for eons. Amsoil severe gear is what I used and many others. You don’t need to add any friction modifiers 

 

3. yes you have the American axle 11.5 if you have a 2500 except maybe some heavy tow package gets the 12” don’t recall the year that happened. 
 

4. I know that’s been posted here before by probably @newdude

 

5. You won’t need a new gasket to add new fluid 

[newdude]

18 hours ago, SoCal Angler said:

Great threads never die!

 

My '23 does not have a drain plug.

I'll be checking the level in the next few days.  

 

A few questions that I do not believe were addressed....

 

1.  If low, is adding the AC Delco 75W-90 the preferred oil to bring fill level to within 0"-.4", so as not to mix oils...assuming GM used the same oil that it sells at retail?  Since 0" is within the specs, is adding oil until it flows out of fill hole an acceptable level?

 

2.  Is the '23 3500 GAS 4x4 HD axle a LS rear axle or something else?  My window sticker says, "auto locking rear differential." If this means that it is not a LS axle...would the added modifiers be a concern when using Amsoil?  I see Amsoil makes a Long LiFe 100% Synthetic Gear oil 75W-90 without modifiers...is this one preferred?

 

3. What are the model #s for the ('23 3500HD Gas models, 4x4) rear axle, front axle, and transfer case?  Are model #s stamped onto axles and transfer case, if so where?  I can only find ON GMC website that it is an 11.5" ring gear axle.

 

4.  Since owner's manual does not provide any gear oil specs (type/qty) for front/rear/transfer case, where can official info be located?

 

5.  Unable to find a part number for the fill plug gasket.  Anyone have the part #?

 

NOTE:  I also found these discussions interesting...wonder if this is the same/similar axle and would it apply to our current axles?

 

Locking Diff Lubricants

 

Oil Level and Fill Plug gasket

 

 

Thanks!

 

 

1 - 88900401 is the GM gear lube 75w90.  Do NOT add any additives to that p/n.  If you filled it to where it ran out, let it come to a slow drip or no drip to get to the 0" range of the spec.

 

2 - All GM HD trucks are the Eaton G80 auto mechanical locker except the ZR2.  ZR2 has an electronic locking diff.  GM calls for no modifiers when using GM's oil.

 

3 - 11.5" on all gas.  

 

4 - Transfer case is spec'd out in the manual.  Page 390.  Dexron VI ATF.  Rear diff is 88900401 75w90, front diff is 19300457 75w85.  

 

5 - Fill plug gasket is re-usable unless damaged.  

Edited February 9 by newdude

[bruceb58]

For my 1st diff change, I am going to put a Banks pan on with a drain plug.

[SoCal Angler]

On 2/9/2024 at 8:36 AM, newdude said:

 

 

1 - 88900401 is the GM gear lube 75w90.  Do NOT add any additives to that p/n.  If you filled it to where it ran out, let it come to a slow drip or no drip to get to the 0" range of the spec.

 

2 - All GM HD trucks are the Eaton G80 auto mechanical locker except the ZR2.  ZR2 has an electronic locking diff.  GM calls for no modifiers when using GM's oil.

 

3 - 11.5" on all gas.  

 

4 - Transfer case is spec'd out in the manual.  Page 390.  Dexron VI ATF.  Rear diff is 88900401 75w90, front diff is 19300457 75w85.  

 

5 - Fill plug gasket is re-usable unless damaged.  

 

Thanks for the info.!!

 

Does this mean that it would be ill advised to use Amsoil Severe Gear oil as it does contain friction modifiers?

 

I know I can reuse the fill plug gasket, but I I wanted to know the part number as I am unable to find it on GM parts website or any other parts locater website. I want to have a spare on hand.

Edited February 11 by SoCal Angler