Trans/Transfercase fluid change

Hey yall, Ive decided to start saving some money by changing the fluids myself instead of getting overcharged, I'm not too sure how long its been since the last Trans fluid change Carfax says 187k and now at 203k but the fluid looks fairly brown. I Also dont know when the last time the Transfer Case fluid was changed aswell. So Before all the long drives over summer I plan on changing everything, So my questions are. Whats the Correct fluid for the Transfer case? Ive heard of ATF or using 5w-30 And would like to know what is the best in the long run. Another thing Should I bother changing the Trans fluid? its only 16k since last change and it seems to be smooth and shifts nicely. I recently changed out both of the diff fluids and it seems go be going well. Any other oil or fluid I need to worry about? Thanks.

4x4 or AWD transfer case? What's the year, make, and model of what you're working on? (Might put it in your signature so it's always there.)

Optionally, post a pic of your 4x4 switch, or of your RPO codes from the inside of the glovebox lid.

If it's the 2-speed AUTO 4wd system, the transfer case takes just under two quarts of Auto Trak II fluid (it's blue).

Fless said:

4x4 or AWD transfer case? What's the year, make, and model of what you're working on? (Might put it in your signature so it's always there.)

Optionally, post a pic of your 4x4 switch, or of your RPO codes from the inside of the glovebox lid.

If it's the 2-speed AUTO 4wd system, the transfer case takes just under two quarts of Auto Trak II fluid (it's blue).

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Will do tomorrow morning. A 2004 GMC Yukon XL 2500 with the 6.0 It has 4WD

If that trans fluid is not nice and red I'd change it. I'd want to see what's in the bottom of the pan too.

Definitely change the trans fluid if it’s brown.

You have the 4L80 / 4L85E trans I believe. It's a good setup with the 6.0L and can take quite a bit of abuse, but no need to find out how much. If the looks brown, DEFINITELY change it out like @tom3 and @Sam Harris stated. I'd drop the pan and replace the filter. If there's nothing sitting in there other than some fine particles and a little fuzz on the magnet, then button it back up, fill with fluid, and see what it looks like.

If the fluid still looks brown after a test drive and hot level check, then a flush is what I would recommend. After that, you'll be good for many miles of road trips.

The transfer case on that model takes regular ATF I believe. I don't recall an AUTO option for the 2500 trucks, but could be wrong. It's been a few years since crawling around one of those. If the truck is new to you and you don't have all the service history, I'd recommend just doing all fluids front to back for the driveline. It's cheap and easy insurance. I'd rather know it's new and clean, than speculate to save a couple bucks.

Be sure to check your owner's manual (available online at GMC) for the fluid requirements.

Do you have the AUTO transfer case? What are your RPO codes that begin with "N..."?

I’ll check when i get home from work, i’ll let you know what the codes were

Should be the NP246 transfer case. I "think" that may have been the only option for those models? I haven't seen a manual transfer case yet.

On the transmission, you can unhook the radiator cooler line and clamp a clear vinyl tubing into a bucket. Run the engine until the tubing starts spitting. That will remove most of the fluid from the torque converter. Drop the pan, change the filter and clean the magnet.

Reinstall pan and dump 5 quarts of Dex VI. Fire up the engine and dump another 5 quarts while running. Shift through the gears and add more ATF if necessary.

That's how I've done fluid changes on my 4L80e trucks. It kinda seems intimidating at first, but it's pretty easy.

Only drawback is you'll need more fluid than a drain/refill. I've been buying the O'Reilly's 5 gallon ATF since I have several of these trucks.