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Thank you dmaxalliTech......

Front Diff-- OEM fluid is 80-90 gearlube. It is acceptable to replace it with 75-90 synthetic fluid. Any quality fluid is acceptable as long as it meets GL-5 requirements. When going to any type of synthetic fluid, its advisable to change the vent cap on the front diff to the "white" cap. This cap is the replacement cap and the black cap is no longer offered. Part No. 12479296 for the cap. The refill capacity for the front diff is 2 quarts.

Rear diff- The 2500HD and 3500 trucks use an American Axle 11.5" rear end. Its available with the Eaton limited slip option (G80). The Diesel engine equiped trucks only come with a 3.73 gear. The 8.1 trucks have either a 3.73 or a 4.10 option. The OEM fluid is 75-90 synthetic lube, commonly referred to as "grape juice" for its smell. A synthtetic lube must be used in the rear axle and it must meet GL-5 requirements. I dont know the additive package of the aftermarket lubes but I would think that the quality lubes contain the necessary additives for the limited slip. It is not necessary to add any additive to the rear end when servicing. Capacity is 4 quarts. It is recommended by Eaton to service the rear axle after the first 500 miles of towing or 5000 miles of driving.

Transfer Case- First, lets discuss the options for the transfer case. If you are driving a 2500 HD or 3500 pickup, you have a NV-263 case(push button shift) or a NV-261 case ( floor manual shift) There is no automatic transfer case in these trucks. The 1/2 trucks and I believe the 2500 (non-HD) trucks will use the NV-241 (floor manual shift), the NV-243 ( push button shift) or the NV-246 case ( auto-trak, push button ) We will concentrate on the 2500HD and 3500 trucks here. The OEM fluid for these is Dex III or equiv. This means that any quality Dex III fluid or synthetic will work. There is no changes necessary to switch to synthetic. Capacity is 2 quarts.Edited by: Diesel Power
 

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changed my front diff fluid over to mobil 1 75-90 synthetic today, also upgraded the vent cap as recommended. was good to see the old gearlube come out, not dirty but some guk on the magnetic plug. now when it gets to 25 below up here, i will feel confident things are right..later, bc


ps, thanks for the indepth info here..worked out great
Edited by: bob camire
 

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Did the front and rear tonight - boy does that oil stink! I bought my truck used with ~40K miles on it - thought it best to change the fluids in case the previous owner didn't. Back end stuff looked real dark but the front was OK! How tight did you'll tighten the front white vent cap - with the nylon threads I had a tough time judging between tight and too tight. Thanks to everyone who posted on the various transfer case threads - it made the change much easier.
 

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I have the '04. It only has 2500 miles on it, but while under it, changing the oil, I checked the front diff, and I have the white vent cap! Does anyone else with the '04 have this? And does this mean I have Syn. in it. Will change both front and rear at about 7000 miles, and will go to syn. in the front. Thanks all.
 

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I think all 04s have the white cap, but I don't think any of them come with Syn in the front.
 

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Can you buy a magnetic drain plug for the rear end as one can for the oil pan? would you use one?
 

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My 03 came with standard length magnetic drain pugs from the factory. Front and rear diff.
 

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I finally got through to a Tech for Chevron/Texaco that had some answers


First contact was the Chevron/ Texaco


Lubricants bussiness Center


1-866-688-8890


This number forewarded me to 1-800-231-6950


Here I taked to a tech looking for the Texaco number 2276 or 2080.


Finally he came back and said the oil is made but it is only sold by GM.


His records show it is not avalible other than from the dealer. Telling him it is 30 dollars a qrt from the dealer I got a real big WHOOA!!


He siad that if I use another lube it way void the warrantee. I'll keep plugging away.
 

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Can someone tell me where this white or black vent cap is located on the front differential. Is it threaded into the differential or on a vent hose that goes up into the engine compartment. I found the vent hose in the engine compatment that comes up from the differential I think, with a black cap on it. Anyone clarify this for me. Also where can I get this part from? Is it dealer only or can I get it through GM Parts Direct? I am going to change fluids in the diffs in the near future, so any info on this would be great. Thanks...
 

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Chevyfreek


Look at the driver's side of the case above where the axle shaft enters the diff. and you will find a screw in black vent cap with a rubber hose attached. Remove the small rubber vent hose from the cap and use a socket wrench (can't remember what size of socket?) to unscrew the cap from the differential. The white cap is used if you are switching over to synthetic gear lube or stay with the black if you decide on the non synthetic lube. Edited by: TC Dmax
 

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OK. I must be a moron. Riddle me this, oh great GM techs:


What's the difference between the GM part no 12378261 synthetic lube @$29.02 / qt from myfriendly local GM stealer and the $8.18 / qt Mobil 1 75-90 synthetic lube at AutoZone? Is there iron-clad proof that if I use the $8 lube I'll void warranty or what? I'm approaching the 5k mile maintenance and would like to get to the bottom of this.


The only things I feel comfortable spending $25 or more / qt are aged in oak barrels for several years.
 

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I know that GM specifies the GM 75W-90 "Grape Juice" for the rear differentials of our trucks but I thought I had read that 75W-140 was to be used for heavy-duty towing applications.


When I checked my owners manual there is no mention of using 75W-140. in any situation. I have searched several fourms and still can not find any reference to any situation where 75W-140 is used. I am too young to be getting Alzheimers!!


Does anyone know of a reference where 75W-140 is specified for our truck and what the GM Specification is??
 

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Is this the right part from GM Parts Direct for the white vent cap on the front differential:



<TABLE cellSpacing=0 cellPadding=3 width=567>
<T>
<TR background="images/trans.gif">
<TD class=reg vAlign=bottom>GM PART # 12479296
CATEGORY: All
PACK QTY: 1</TD>
<TD class=reg vAlign=bottom>CORE CHARGE: $0.00
GM LIST: $20.56
OUR PRICE: $11.72</TD>
<TD align=right><!--< name="p12479296" ="text" value="1" size="2" maxlength="3">
< ="" name="parts" value="12479296">--></TD></TR>
<TR vAlign=top background="images/trans.gif">
<TD class=reg colSpan=3>DESCRIPTION: CONNECTOR
</TD></TR></T></TABLE>


If someone could verify this for me before I order it. Thanks....
 

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Haven't done transfer case yet. Seems straight forward....like the diff. Do I need to drop the skid plate? Haven't looked around for drain and fill on transfer case. Pics anyone?
 

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Is there a link with some pics of this fluid change or would someone (more mechanically and technologically advanced than me
) be willing to post the procedure and all the necessary parts, tools, etc. needed. Preferably a step by step thing with some pics (my simple mind works better with pictures
).


I already had to have my front vent replaced because it was leaking. Do I need to replace it again when I change to synthetics?


Schaeffer's all the way!!
 

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For those that have changed rear diff lube, did you remove the rear cover, or does the magnetic drain plug catch all of the break-in metal?


I know that in most vehicles, you still end up with a lot of slush in the bottom of the case, even with a magnet...
 
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