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Discussion Starter #1
I'm sure it is in here somewhere but I can't find it.
I think I've done it on a 1974 Chevy 4x4, long time ago though.
I would appreciate it if someone would refresh my memory for these new trucks.
I guess saying the last time i did it was on a 74 kinda tells my age. Damn good truck and it still runs. A little rusty though.

Thanks
Billy
 

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The drain plug is on the bottom of the rear diff, I think it's 3/8 square IIRC. The fill plug is on the rear diff cover, facing the rear of the truck. Just loosen the fill plug, remove the drain plug, drain, replace the drain plug and refill with your selected GL5 gear lube. Edited by: Hound
 

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Discussion Starter #3
Hound,
Thanks
I was hoping it would be pretty straight forward.
Just wanted to make sure I went about it the right way.

Thanks again,
Billy
 

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Fill it up with SAE 75W-90 Synthetic Axle Lubricant GM P/N 12378261 (grapejuice)



<TABLE width="100%" border=1>
<T>
<TR>
<TD vAlign=top align=left>
<UL =NONE>
<LI>Rear Drive Axle (8.6") </LI>[/list]</TD>
<TD vAlign=center align=middle>


2.03 liters</TD>
<TD vAlign=center align=middle>


2.15 quarts</TD></TR>
<TR>
<TD vAlign=top align=left>
<UL =NONE>
<LI>Rear Drive Axle (9.5") </LI>[/list]</TD>
<TD vAlign=center align=middle>


2.6 liters</TD>
<TD vAlign=center align=middle>


2.75 quarts</TD></TR>
<TR>
<TD vAlign=top align=left>
<UL =NONE>
<LI>Rear Drive Axle (9.75") </LI>[/list]</TD>
<TD vAlign=center align=middle>


2.84 liters</TD>
<TD vAlign=center align=middle>


3.00 quarts</TD></TR>
<TR>
<TD vAlign=top align=left>
<UL =NONE>
<LI>Rear Drive Axle (10.5") </LI>[/list]</TD>
<TD vAlign=center align=middle>


2.6 liters</TD>
<TD vAlign=center align=middle>


2.75 quarts</TD></TR>
<TR>
<TD vAlign=top align=left>
<UL =NONE>
<LI>Rear Drive Axle (11.5") </LI>[/list]</TD>
<TD vAlign=center align=middle>


3.62 liters</TD>
<TD vAlign=center align=middle>


3.83 quarts</TD></TR></T></TABLE>
 

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GMCSID..i HAVE A 2000 GMC 2500 4/4 4DREXTCAB AND I WOULD LIKE TO KNOW IF i CAN USE CASTROL SYN ALXE LUBE 75W-90 GL5 IN REAR DIFF OF MY TRUCK IS IT COMPATIABLE TO GM SYN AXLE LUBE GM PART NO 12378261..WITH THANKS
 

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Karl, GM want's you to use their lube and nothing else. If you search around here most people have changed brands with sucess. I found some comments about this subject.


<center>
Michael Asmussen said:
Note from Michael Asmussen, Torque Control Products Division of Eaton Corp.

We recommend the following lubrications for our locking differentials:

1)Texaco 2276; Synthetic 75 W90; GM Part # 9986115
2)Texaco 9622; Mineral based 80W90; GM Part # 9985290
3)Texaco 2080; Synthetic 75W140 (heavy duty applications); GM part # 9985991

Note - All of the above lubes are preblended with friction modifier. No additional modifiers are necessary or recommended. As far as other lubes are concerned, any standard GL 5 lube will work, but the units perform optimally with the three listed above.

[Comment from Castrol:] Thank you for contacting Castrol regarding Syntec 75W-90 GL-5 gear oil in your Eaton Automatic Lock. You may use SYNTEC gear oil with full confidence.

[Comment from Mobil:] Mobil 1 Synthetic Gear Lubricant meets the GL-3, GL-4 and GL-5 API ratings. If the manufacturer requires the use of a GL-4 rated lubricant ONLY, then you should not use Mobil 1 Synthetic Gear Lubricant.

Ralph Holmquist said:
From Mr. Ralph Holmquist of Eaton, the maker of the locking differential:
"The maintenance schedule for the rear axle was developed by American Axle &
Manufacturing and GM truck based on multiple tests. The Eaton locker does
not require additional maintenance nor does it add heat to the lube. The
lube will darken due to the carbon wear on the clutch surfaces, much the
same as a disc brake pad & rotor. This does not damage axle components such
as seals or bearings. However, a new axle can produce excessive
temperatures (plus 350 degrees F) due to the ring & pinion breaking in that
will break the lube additives down. Avoid high loads, trailer towing and
high speed extended driving during the initial break in of the vehicle.
After the break in period axle temps will level at a much lower figure.
Lube changes are a good idea because the additives are replenished and
contaminates such as casting sand are eliminated. The axle is filled at the
factory with a synthetic 75w90 GL5 rating made by Texaco under part # 2276.
The GM service # is 12378261. This is the only lube we have done extensive
testing with to insure locker compatibility. The only negative to using one
of these other lubes is an increased potential for clutch chatter. This
really doesn't hurt anything and can be corrected by changing the lube. I
noticed in the latest GM owners manual the term "or equivalent" when
referring to the lube specification. Look for a GL5 rating on the bottle to
make sure the ring & pinion, seals & bearings are protected. Limited slip
additive is not needed

</center>
 

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you might want to change it after driving for awhile to warm it up
 
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