# 2500HD diff fluid replacement



## ChevKid03 (Dec 23, 2007)

Quick question.... I have an 03 Silverado 2500HD with the G80 Locker and would like to change both front and rear diff fluid as well as transfer case. (just did tranny last month). My question is, what type of fluid is supposed to be used in the differentials? I know that gear fluid is needed, but not sure if I need something different due to the fact that it has the G80 and possibly limited slip? 

I know that the transfer case will have to come from GM (blue stuff since it's push button), but any help on the diffs would be GREATLY APPRECIATED!!!


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## 70monte (Feb 5, 2008)

If you have the owner's manual it will tell you what kind and weight fluid you need. It will probably be a 80W-90 in weight and the fluid might have to be partially synthetic on the newer trucks. I seem to remember something about people were having trouble finding diff fluid that met the specs GM required at places other than the dealer. I know on the OBS trucks with the G80 posi, it doesn't require anything special for the posi. Just regular 80W-90 fluid.

Wayne


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## Spitz (Feb 28, 2008)

Pretty sure the rear needs a synthetic lube (75w90 i believe).. And i believe the front can be filled with just a regular 80w90.. The transfer case im unsure about, but 95% of the trucks i've come across run their atf in the transfer case as all the fluids now are a synthetic..


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## B&B (Nov 4, 2006)

Front diff:

80W-90 or any GL5 rated gear oil. Upgrading to full synthetic isn't a bad idea if you dont mind the extra expense.

Rear diff:

75W-90 synthetic No additives necessary, G80 or not.

Transfer case:

Dexron III ATF is the factory called fluid. A better alternative is Royal Purples Syncro Max MTL fluid. Solves the problem that these T-cases have with vaporizing the ATF and expelling it from the vent hose.

_*DO NOT PUT THE BLUE GM "AUTO TRAC" FLUID IN THIS T-CASE!! *_

Just because a truck is equipped with push button 4X4 doesn't make it "auto" equipped. The AutoTrac fluid is for the 1/2 tons equipped with the actual on demand AutoTrac T-cases.


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## ChevKid03 (Dec 23, 2007)

B&B;530232 said:


> Front diff:
> 
> 80W-90 or any GL5 rated gear oil. Upgrading to full synthetic isn't a bad idea if you dont mind the extra expense.
> 
> ...


Not to seem dumb, but can I ask what GL5 stands for? I'm going to hit up the local parts store today to buy some supplies and get this done this week.

Also, I'm just curious as to why so many limited slips diffs need an additive and mine does not? Sorry to be so quick to respond, but I am just curious because I need this truck lasting a few more years for me and am pretty anal about things... If i don't know how it works, I try to figure out everything I can about it before touching it.

And about the GM BLUE fluid.... thanks alot for that tip! I guess it makes sence since the last truck I used that in was a 2000 S10 ZR2... Not as heavy duty...


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## B&B (Nov 4, 2006)

Not a dumb question at all CK...

The term GL5 is the API rating of the oil... just like engine oil. GL5 was the most current designation for gear oil at the time our truck was produced. GL6 is now the highest rating. So you can use any oil meeting the GL5 or GL6 rated specs. It'll have the GL rating right on the bottle if you look at the label.

GM no longer recommends additives in the HD trucks after they began using synthetic oil in the rear ends along with changing the clutch material to carbon fiber in the G80 Gov-Loc's. SO no additive should be necessary for your truck. But I have heard of several Gov-Loc's with the old style clutches finding their way into 01 and newer trucks...so if by chance after changing the rear fluid you find that the Gov-Loc "chatters" or severly binds up during a tight turn, yours may have the old style clutches. If you find thats the case, simply drain a little fluid out and add the additive, it wont hurt a thing if you run it without the additive though.


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## ChevKid03 (Dec 23, 2007)

B&B;530466 said:


> Not a dumb question at all CK...
> 
> The term GL5 is the API rating of the oil... just like engine oil. GL5 was the most current designation for gear oil at the time our truck was produced. GL6 is now the highest rating. So you can use any oil meeting the GL5 or GL6 rated specs. It'll have the GL rating right on the bottle if you look at the label.
> 
> GM no longer recommends additives in the HD trucks after they began using synthetic oil in the rear ends along with changing the clutch material to carbon fiber in the G80 Gov-Loc's. SO no additive should be necessary for your truck. But I have heard of several Gov-Loc's with the old style clutches finding their way into 01 and newer trucks...so if by chance after changing the rear fluid you find that the Gov-Loc "chatters" or severly binds up during a tight turn, yours may have the old style clutches. If you find thats the case, simply drain a little fluid out and add the additive, it wont hurt a thing if you run it without the additive though.


Thanks Alot B&B! I'll let you guys know how it goes...


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## tuney443 (Jun 25, 2006)

B&B;530232 said:


> Front diff:
> 
> 80W-90 or any GL5 rated gear oil. Upgrading to full synthetic isn't a bad idea if you dont mind the extra expense.
> 
> ...


EXACTLY----another alternative for the lube for the TC is 5-30 engine oil and to add an extra quart through the speed sensor plug which is above the regular fill plug.So now you will have 3 qts.This comes right from the TC manufacturer---GM dealerships don't have this info.


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## B&B (Nov 4, 2006)

tuney443;531448 said:


> EXACTLY----another alternative for the lube for the TC is 5-30 engine oil and to add an extra quart through the speed sensor plug which is above the regular fill plug.So now you will have 3 qts.This comes right from the TC manufacturer---GM dealerships don't have this info.


Yep, I'm totally aware of it as well tuney.. many guys are running the 246's on 5-30 and a qt. overfull with good success. I still prefer using the RP Syncromax instead though, been running them this way since '02 with excellent results..ie: no burned up T-cases to date.


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## ticki2 (Jan 10, 2006)

B&B;530232 said:


> Front diff:
> 
> 80W-90 or any GL5 rated gear oil. Upgrading to full synthetic isn't a bad idea if you dont mind the extra expense.
> 
> If you go with synthetic in the front , which I recommend, make sure it has the white vent cap , not black on the diff. If it is black you can get the white one from the dealer.


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## lilweeds (Aug 3, 2007)

If you run motor oil it should be NON Detergent in the transfer. The detergents aren't good for the gears.


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## dlcs (Sep 2, 2004)

B&B;530232 said:


> Just because a truck is equipped with push button 4X4 doesn't make it "auto" equipped. The AutoTrac fluid is for the 1/2 tons equipped with the actual on demand AutoTrac T-cases.


Not just for 1/2 tons. My '99 newer body style 2500 had the "auto trac" transfer case and used the blue fluid.


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## B&B (Nov 4, 2006)

dlcs;532113 said:


> Not just for 1/2 tons. My '99 newer body style 2500 had the "auto trac" transfer case and used the blue fluid.


Sorry, MOST were 1/2 tons..

'99-2000 Silverado body style 2500's (2000 Suburbans included) did also have the Auto Trac T-case.


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## scottL (Dec 7, 2002)

ticki2;531902 said:


> B&B;530232 said:
> 
> 
> > Front diff:
> ...


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## tuney443 (Jun 25, 2006)

rsvees;531915 said:


> If you run motor oil it should be NON Detergent in the transfer. The detergents aren't good for the gears.


Not true at all.Why would you think detergents are bad for gears?I run Mobil 5/30 synthetic in mine--no issues.I remember reading the article from New Venture stating to use engine oil in their boxes--either dino or synthetic--nothing about non--detergency.


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## ticki2 (Jan 10, 2006)

scottL;533228 said:


> ticki2;531902 said:
> 
> 
> > What's with the color cap? Why one over the other???
> ...


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