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I have approx 600 miles on my truck now,will be towing my fiver approx 1000 miles here in a few weeks. Manual states change the fluid at 500,do i need to stop and do this or wait till i get to my sunny destination. Where can i get it changed other than the dealer and what fluid do i use? Thanks in advance
 

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Coach,


I would wait until you get back from your trip. The recommendation is to change it after at least 500 miles of towing. As to fluid, a good synthetic 75-90 Gear Oil is what you want. AV Lubricants carries Mobil-1, my local Wal-Mart carried a Penzoil synthetic 75-90, which is what I went with. For very hot/heavy towing GM recommends a different weight oil, but I can't remember the weight. I am sure someone here will chime in soon.


It is easy to change, as there is a drain plug at the bottom of the differential, and an easy to reach fill plug at the top. Quantity, I believe, is about 3.5-4.0 quarts, but I may be mistaken on that. When I changed mine I also put a Mag-Hytec differential cover on. Gives 8 quart capacity to the diff, a magnetic dip-stick for collecting metal shavings, and then there is the cool factor, which can never be taken lightly!



Hope this helps.


John
 

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For heavy towing I believe the recommended gear oil is 75w-140.


Joe
 

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Ditto on the 75w-140, if you have a 4x4 and do the front diff, make sure you get the white cap from the dealer if you use synthetic lube. I was surprized at the amount of crud that came out of mine after just one winter, wish I had odne it sooner.


Mark
 

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Coach, notice your from MI, what part? I might of asked you already, sorry if I did. Anywho, you can change fluid yourself, drain pan and some parts from your local expert
and your on your way


Eric
 

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dmaxalliTech


I went to the local Chevy dealer and the parts guy had never heard of the white differential cap for my 4X4
. I would like to switch to a synthetic 75W90 for the front. Do you have a part number for the cap?


Also, gmparts.com has the 75W90 for half the cost my local dealer charges.


Thanks.
 

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Can't beat that. I want to do the front and rear so do you think a total of 10 quarts?
 

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Fish2Max. 6 Qts is all you need for the front and rear. 4 qts in the rear and 2 qts in the front. Dmaxallitech price is a real good one. My dealer wants $30.00 a qt for the grape juice alone.
 

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Mobile 1 for me also. Its great lube, and much cheaper than the grape juice. I know, I know.....its not GM specific..
....I don't care either. Its quality, GL-5 rated gear oil, and will work just fine, IMO.
 

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GMC-2002-Dmax said:
I used Valvoline Synthetic GL5 rated diff. fluid.


I have The G80 locker and have had no problems to date.


T
NY

Do you also need any of the GM Friction Modifier?
(I don't have a Helms for my '04 yet)

Thanks!

T.
 

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The G80 does not require a friction modifier.


Mark
 

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What is the differential cap you guys are talkin about ???? for the front or the autotrac 4x4 ? Also my rear end does not have a drain plug
I did change the fluids in the auto trac at 50k as well as the front diff. I need to change the rear fluid as I have just topped it off to this point. 56k. What kind of form a gasket is best used to re seal. I spend to much time in the woods so I have stayed away from the aluminum rear end covers. I have a 02 and it seems my manual is missing a few points like changeing the Allison spin on filter at 7500 miles
I did it at 50k and changed 8qts (pan drain). The filter had boo coo metal shaveings. I dented the filter at 55k so I did the same thing again and it had metal shaveings it still
NAPA has the spin on filters for $18. Has anyone changed the inside tranny filter ??? I see on the Allison site they only recommend changeing it at overhaul.
 

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I used Redline Synthetics from front to rear.75w-90 gear lube(4 rear, scoosh over 2 front.) 15W-40motor oil. Changed diffs at 750 miles and then again at 20K and then at 50K. No additives required. Works perfect. $6.95 a qt.



Edited by: Duramax Dually
 

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BlueMaxxxx,


The HDs don't come with the AutoTrak. Do you have a half ton?



There is a black vent cap on the top of the front diff that is incompatable with synthetics. If you run synthetic in the front, you need to change to the white cap Eric mentioned about. One thing I have noticed is that ALL of the synthetic gear lubes stink.
Redline, Grapejuice, Amsoil, it doesn't seem to matter who's. Maybe it's the additives to make them GL5?
 

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I have a 2500 HD ext cab SWB. I guess I gotta remove the skid plate and take another look at the front diff. When I drained it I just used the recommended conventional gear lube. The 4x4 unit which I though was a autotrac, maybee I'm confused though. It took a special blue fluid. GM part # 12378508 $6.96 qt. Do you have the shift on the fly ? Dave
 

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BlueMaxxxx,


The rear diff has a drain plug on the very bottom of the diff itself. Not on the pan. It should take a 3/8 ratchet drive. The plug on the pan is for checking the fluid level, and re-filling. Should tale 4 quarts.


Its obvious by your posts you have an auto transfer case. As chuntag95 stated, the HD's do not come with the "autotrak". They are two different animals. Your 4X4 buttons should have 2Hi, 4Hi, and 4Lo. Right ? Not a button that says "Auto". I am not sure if the auto transfer case takes a special fluid or not. The manual case just takes Dex III.
 

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BlueMaxxxx said:
I have a 2500 HD ext cab SWB. I guess I gotta remove the skid plate and take another look at the front diff. When I drained it I just used the recommended conventional gear lube. The 4x4 unit which I though was a autotrac, maybee I'm confused though. It took a special blue fluid. GM part # 12378508 $6.96 qt. Do you have the shift on the fly ? Dave

There is a pushbutton transfercase that will shift on the fly, but is NOT the auto track. It uses standard Dexron III transmission fluid. The differential uses 80-90W Gear lube, but most go with the 75-90W or the 75-140 depending on location, towing, etc. As I recall, the manual is confusing about who has the autotrac, but it is not offered in the 3/4 and 1 ton units.
 
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