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I just got a 2008 gmc 2500 duramax and i wanna change the transfer case fluid. What fluid should i use and how much?


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The transfer cases in these years DMAX trucks are designed for Automatic Transmission Fluid...Dex III 1.6 - 2.0 quarts if I remember correctly. Do not use the Autotrac fluid as we don't have autotrac transfer cases in the HDs, only in the 1500s. There might be better suggestions on fluids out there but the owners manual suggests the above.
 

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Use the same fluid as your transmission or you can use 5W-30 synthetic engine oil. Search on here and you will find a lot of info.
 

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GoBlowSnow is right about Dex III in that our trucks don't use it in the transmission or the transfer case. It calls for DEX VI in both. It is best to use the exact same thing in both the transmission and transfer case because they often exchange fluids. If you use engine oil or gear oil there is a chance of it getting into the transmission which could turn a very good transmission into a rebuild job in short order.

If you have changed to another fluid in your Allison like Transend then you need to put that in the transfer case too. In normal use the transfer case isn't very picky about what you use in it. It really should match the transmission though.

You will need 1.5 liters or 1.6 quarts. Don't overfill it. All that gets is more heat and foam which can reduce life, not extend it.
 

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GoBlowSnow is right about Dex III in that our trucks don't use it in the transmission or the transfer case. It calls for DEX VI in both. It is best to use the exact same thing in both the transmission and transfer case because they often exchange fluids. If you use engine oil or gear oil there is a chance of it getting into the transmission which could turn a very good transmission into a rebuild job in short order.

If you have changed to another fluid in your Allison like Transend then you need to put that in the transfer case too. In normal use the transfer case isn't very picky about what you use in it. It really should match the transmission though.

You will need 1.5 liters or 1.6 quarts. Don't overfill it. All that gets is more heat and foam which can reduce life, not extend it.
Thank you for this info. I didn't realize that the transfer case fluid could get mixed in with the ATF and such.
 

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There are seals separating the two. There is always a double lip seal on the front of the transfer case and often a single lip seal on the rear of the transmission. The way you find out that the seals have failed is by having an excess of fluid in either the transfer case or transmission. If you are lucky there will be an oil leak between the two that will alert you first but not always.

It is an expensive way to learn if the fluids are incompatible. Since it is easy and cheap to fix this so that there isn't any chance of cross contamination, it is just a reasonable thing to do.

There are people who use non-compatible fluids. It is their choice of course. We just need to be aware of the potential consequences before doing something like this. If you understand whatyou are doing and chose to do something non-standard then that is your prerogative.
 

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My LLY has 300k + miles on it, and I service the T/X case about every 30k or so.

When running ATF, the fluid always had metal in it.

I switched to 0w/20 motor oil about 100k ago.... and now theres no more metal in the drain oil.

My LML is draining pretty clean, with Delvac 1 ATF in there. I'll stay with the ATF in the LML, for now.

YMMV
 
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