I want to change my transfer case fluid. I have an auto four wheel drive case. The book says to use a special fluid that apparently I can only get at the dealer. I want to use synthetic. Are there any products out there I can use? Also I read something about a white vent cap on the front diff when using a synthetic fluid. It was in a Dmax area but does it apply to all? Thanks for any info.

Mobil 1 synthetic ATF

Yup, GM just uses ATF. Pick your fave.

if it is an automatic t-case you should put the gm autotrack fluid in it ,it is blue it has something to do with the viscus clutch in the t-case

Are you talking about the full time 4wd systems? I don't think suburbans, or GM trucks ever had that option. Atleast I've never heard of GM using is viscous clutch in any of them. His should have and NP20X transfer case, not that dissimilair to earlier models.

The transfer case is a NVG246.

Ain't the internet great...I guess I was wrong....

NVG246

Type: Part-time, aluminum, chaindriven case

Low range: 2.72:1

Applications: ’98-present GM ½- and ¾-ton pickups, Tahoes, Suburbans, Yukons, Denalis, and Escalades

GM knows that sometimes you have more important things to do than pull levers and lock hubs, so it worked with New Venture Gear (same company as New Process; they just had to change the name) to come up with what it calls the Autotrac system. Autotrac allows you to select 2-Hi, 4-Hi, Neutral, and 4-Lo like before, but now you do it with buttons instead of a floor-mounted shifter. That in itself is nothing special, so in addition to the traditional transfer case positions, you get an automatic mode that will bias torque to the front or rear wheels as needed. This system works through a computer-controlled clutch pack mounted to the front output of the NVG246 and will send power to the front wheels if the rear wheels lose traction. Press the Autotrac button and you could go from cruising down Main Street to swamping through the local mud pit without taking your hands off the wheel. The major drawback of this “select it and forget it” system is that the front driveshaft is always spinning. That’s why most lift kits for these trucks require a new front driveshaft to cure vibration problems.

Chain driven? Does that mean that there's a chain in the T-case involved in driving the gears, like a timing chain? How durable would that be?

My owners manual says that optionally there could be buttons to select between 2h/4h/4l and shifting would occur automatically once possible, but that doesn't seem to be like the Autotrack system. Maybe that's a different T-case prior to '98. Is that is also a chain driven one?

Texas Diesel Guy

Thanks for additional info. Now one more question, when I'm in 2H is my front driveshaft still supposed to turn? I went to synthetic in front and rear diffs and now I have a slight leak from the input shaft seal and the oil is being slung around that area. I thought when not in 4wd the frontdrive shaft is not supposed to turn. Does it turn because of the clutches or do I have a transfer case problem?

That article I found for you contains everything I know about your transfer case, its all new to me! sorry.