Changing Transfer Case Fluid Guide

[MountaineerTom]

Guide posted here for people to have access to until they get posted in the appropriate section here at GM-TC.

 

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Changing Transfer Case Fluid

 

Changing the transfer case fluid is a pretty straightforward job. If you have the manual transfer case (lever actuated), use DEXRON-III Automatic Transmission Fluid. If you have an automatic transfer case (push button actuated), you should use the fluid that GM recommends. Some owners’ manuals may say to use Automatic Transfer Case Fluid (GM Part No. 12378396), which is a reddish colored fluid. GM has a new Auto Trak II Transfer Case Fluid (GM Part No. 12378508), which has a bluish color to it. The newer fluid has better friction modifiers. While your doing the job, it’s a good idea to change the drain and fill plugs (GM Part No. 15032997) out too.

 

First thing you should do is remove the transfer case skid plate for easier access. Only four bolts to remove. (15mm)

 

After removing the skid plate, the drain and fill plugs (18mm) will be very easy to get to. Remove the plugs and let the old fluid drain out.

 

All that is needed to do now is reinstall the drain plug, torque to 15 ft. lbs., and refill the transfer case with fluid until the fluid level is even with the bottom of the fill hole. Basically, fill it up until the fluid runs out the fill hole. It takes almost 2 quarts to fill it up. To make the fill up easier, you may want to purchase a pump at a local auto parts store. These are very handy, don’t cost a lot, and will fit on gear oil bottles for when you go to change your differential fluids.

 

If you have an older model automatic transfer case, yours may have the older, reddish fluid in it, like mine did. If you change to the new Auto Trak II fluid, GM recommends draining the red fluid, refilling with the new blue fluid, drive a minimum of 5 miles, drain again, then refill again with the new blue fluid. My guess is that method is to help flush out all the older, red fluid. That is how I did my truck. I found a place here I could drive around and switch in and out of 2WD and 4WD a few times. I also reused my original drain and fill plugs after the first drain, but replaced them with new ones after the second drain. The blue transfer case fluid cost $6.11 per quart, and the plugs were $5.26 each at my dealer.

[Elwood 2000]

Why replace the plugs? Did you have thread problems?

 

Nice pics., thanks for your time on this issue.

[sgiangregorio]

Great info Tom, thanks for taking the time to post it. Did you put the truck on ramps or jackstands or anything? I'm just wondering how it affected the truck being "level" when you refilled it.

[MountaineerTom]

Your quite welcome. I enjoy taking the pics and doing the write-ups.

 

I didn't use ramps or anything, just crawled under while it was in the driveway. My driveway is not exactly level, so I filled it up until it ran out the fill hole, put the old fill plug in, moved it out on the street where it's level, and checked again. I don't remember for sure, but I think I didn't have to add any more even after moving out on the level streeet and checking it.

 

I decided to change the plugs because they were fairly cheap and they had them in stock. They come with some caulking type sealent already on the threads, but you could put some on the old ones or some teflon tape. I've had bad luck using teflon tape acouple times. It was my own fault though, I used too much on the threads and when I installed the bolt, caused the aluminum thremostat housing to crack on the old Beretta we used to have.

[SilveradoWV]

I probably have the red in mine, and was considering putting in some Synthetic Dexron III! Do you think there would be any harm or advantage to that over plain Dexron III??

 

Thanks for all the articles Tom!

[JayMan]

Anything with clutches in it (Like the Gov-Lok rear end or the AutoTrac transfer case) is picky about what type of fluid you can use. Use the wrong fluid at your peril as the clutches can slip, chatter, and glaze!

 

If you're familiar with wet clutches and wet brakes used in certain tractors, backhoes, skidders, etc, you'll know what I mean. Very, VERY expensive to fix!

 

Yeah, been there, done that.

[99pewterz71]

I had the transfer case seal replaced and noticed on the bill that the mechanic put Synthetic gear oil in it. I'm getting the fluid to replace it but was wondering how much damage would occur if left in too long. It was done on a wednes and today is friday. I won't get to it until tomorrow possibly.

[RyanbabZ71]

99 did you ever put it into 4wd?

[JayMan]

99:

 

Do you have the AutoTrac transfer case? If so, then ONLY use the approved AC Delco AutoTrak II fluid. This stuff is blue in color, like a Smurf. I'm not sure if it's a synthetic, I asked GM and they're very reluctant to answer questions like that. I could see them blurting out something like :

 

"Oh sure, we use Brand X synthetic fluid but branded to our AC Delco name. Why not buy Brand X fluid at one third the price?? Oops, I guess I shouldn't have said that!" Yeah, right!

 

If you have the floor-shift transfer case, it needs the regular Dexron III ATF, which is red in color. So you can use any regular or synthetic DexIII ATF.

 

IF you do have the AutoTrac and the mechanic put in "synthetic" fluid (Whatever that is, is it ATF?), drain and refill with the proper AC Delco fluid. Drive around for a week or so and drain and refill AGAIN.

 

If you don't, the regular 4WD HI and 4WD LO modes will still work, but the AUTO mode will stop working.

[MountaineerTom]

Yeah, I think I'd stick with the Auto-Trac fluid too (which I did). I think it says in the owners manual that it is synthetic, maybe not thought, can't remember. It was around $6 a bottle, but I only needed a little over 2. I bought 3 bottles.

[Highbeam]

It is also possible to have the 243 transfer case that is a push button controlled non-autotrac transfer case. This TC, as with the floor lever equipped version, takes dex3. I used mobile1 synthetic ATF about a year ago and everything is working nicely.

 

One missing point of your write up is that when you pull that lower drainplug the TC fluid will shoot out of the large hole a long ways. Be sure to place your drain pan with this in mind.

[MountaineerTom]

Good points. Thanks.

[JayMan]

It is also possible to have the 243 transfer case that is a push button controlled non-autotrac transfer case. This TC, as with the floor lever equipped version, takes dex3. I used mobile1 synthetic ATF about a year ago and everything is working nicely.

 

One missing point of your write up is that when you pull that lower drainplug the TC fluid will shoot out of the large hole a long ways. Be sure to place your drain pan with this in mind.

If the pushbutton row has a button labeled "AUTO 4WD" then you MUST use the AC Delco AutoTrak II fluid. Otherwise any regular or synthetic Dexron III ATF.

 

Ah, what the heck is the point of working on your own equipment if you don't have motor oil or transfer case oil or hydraulic oil gush all over you? It washes off ... eventually.

[papatitis]

www.gmpartsdirect.com has the autotrac II fluid for $3.51 per quart. just enter part # 12378508

Just a little FYI

[traxion]

How do you know if you have an auto trac TC or not? If I had like avis change the TC fluid could I trust that they would put the correct fluid back in?