NP246 Autotrak in a K1500 99 Suburban..... is this bad news, good news, or wha?

[redfishsc]

So I have this nice 99 Suburban with 230K miles on it. I got it basically for free from a friend, had to immediately swap the head gasket, PS pump, alternator, front U-joints, and also did the MFI upgrade.

This one has the "2Hi 4Lo 4Hi Auto4WD" pushbutton option. The buttons have already fried themselves once in the past few years, my friend had replaced them about a year ago. Light bulb heat?

Anyhow, here's a few questions for those of you who have helpful info. And yes I have done a search of the forum, just also mining around for more opinions/experiences.

1) Is the Autotrak 2 fluid (AC Delco original) the only fluid that works in these?

2) How often should I swap the fluid in this, if I seldom/rarely use the 4WD? (2Hi 99.99% of the time)?

3) Can this case be reasonably swapped with a lower-tech (more reliable) unit? If so , which do you recommend? I don't need the "auto4WD" option, it nearly never freezes where I live.

4) Does this NP246 make the 4L80e swap more difficult, if that day comes? Thankfully the trans behaves well and the fluid looks brand new.

 

[df2x4]

1.) Yes.

2.) I'm not sure about the factory recommended fluid change intervals, but I've seen a lot of people say every 50K miles or so. My Suburban has the NP243 and I'm pretty sure I just changed the T-case fluid for the first time in it's life at 150Kish miles. It was nasty, but everything is fine. I'm sure someone here knows the real GM recommended interval, though.

3.) No idea...

4.) Once again no idea, but I'm curious about that. A quick google search suggests that you can swap an 80E NP241 input shaft into an NP243, but I can't find anything about the NP246 regarding an 80E swap.

 

[Coveman]

I have the 246 in my burb. it takes Autotrac II (blue) and should be checked / topped off every 12 months according to the owners manual-- it doesn't offer a change frequency. Autotrac II has a friction modifier that the 246 requires.

the online manual notes the "transfer case" takes dextron 3, but it doesnt break out the different Autotrac requirement, could be why there is some confusion around the topic.

I swapped my fluid when i fixed the shaft seal around 75k, it was pretty clean looking to me. 2wd uses the fluid for lubrication as well, dont let her go dry or crusty.

 

[Dave Aley]

4) Does this NP246 make the 4L80e swap more difficult, if that day comes? Thankfully the trans behaves well and the fluid looks brand new.

The 4L60e has a 27-spline output, and the 4L80e has a 32-spline. You can buy a 32-spline input shaft for your NP246 for about $75. You may need to do some research to figure out the correct bearing to use with the input shaft. It means you have to tear into the transfer case to swap the shaft, which isn't terribly hard but takes some time. Lots of people have done the 4L80 swap with the NP246, and I haven't heard a lot of people complaining about it, so I'm guessing it behaves well.

Sounds like a screaming deal for a nice truck. Congrats!

 

[redfishsc]

Counting all the fluids, a handful of tools, and replacement parts I've put on it, I have about $1700 in it now. But I also have a nice truck with lots of new parts. In my area this truck would be on Craigslist for around $3k.


Unfortunately the 4wd doesn't work properly I found out this morning. Too early to diagnose, I started a separate thread about it.

 

[Supercharged111]

Autotrack t case has a clutch pack inside. We have autotrack in our 07 Envoy and I changed the fluid around 63k and it was time. My manual states 50k normal and 100k severe IIRC. It only takes 2 quarts and Napa had it in stock, I'll do mine again at 100k. If I were you, I would just tear into your existing case to rebuild it. T cases are easy.

 

[redfishsc]

Ok. I love easy lol. Autotrac has clutches, so there's a little complexity there but I'm not sure how much

 

[Supercharged111]

Dick all, it's just 1 pack. That's the only thing that makes it more complicated than a regular t-case.

 

[TexasT]

I did an over haul on the np246 when ours leaked all the fluid out due to the pump rub issue(and pretty much ate itself up inside).

I had bought another np246 out of a half ton. As mentioned above the half ton is a 27 spline while the 2500 with the 4l80e is 32 spline. These are interchangeable but will require the tc to be split. Not hard but does take some patience to get the internal snap ring behind the rubber plug out to get the halves apart. The real fun is putting it back together. Again not hard but it will try your patience.

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[TexasT]

Pix of the hole(fixed with some jb weld), the pieces that were in there, the special pump half with the "feet" to prevent the pump rub, and the big bearing with no ball separators they I guess melted out as there were just gone.

And not sure if you "need" the autotrack II fluid(smurf fluid as it is blue) but everywhere I read about it said you do so I figured why chance it over a few bux. and ordered a few quarts off the interwebz to have on hand.

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