HOW-TO: Drain and Refill Your Transfer Case

[misterp]

The NVG-149 transfer case contains just under 2 quarts of light-weight lubricating oil, and this fluid must be changed at regular intervals. Normal service is listed as 50,000 miles, but it is not unusual to find an SS with a noisy transfer case (even with as little as 10,000 miles) and quiet its operation dramatically by draining and replacing the fluid. Most conservative mechanics will recommend fluid inspection and or replacement at 40,000-miles, or even sooner in severe-duty or dedicated towing applications.

 

The transfer case comes from the factory filled with Dexron-III ATF, however a much better lubricant recommended for use in the NVG-149 transfer case is a pale-blue synthetic lubricant sold by General Motors under the name AutoTrack II, it is readily available at any GM parts counter for $9-11 per quart. Regardless of your choice of fluids you will need two quarts.

 

If you choose to continue using Dexron-III ATF in the transfer case: expect to change it more frequently as it will not give as long a service life as AutoTrack II; in my own experience I have found that changing the ATF in the transfer case at the same time as servicing the transmission to be a very good rule of thumb, and to do this every 12-months or 20,000 miles, whichever comes first. Your needs may vary depending on your torque converter (high-stall converters produce more sheer force and heat), monthly mileage, and extra towing/hauling duties.

 

Servicing your transfer case is a very easy and straightforward chore, no prior automotive training is necessary - if you can turn a wrench, you can competently change your transfer case fluid with the help of this how-to guide.

 

You will need 2-quarts of GM AutoTrack II fluid, a small drain bucket or catch can, a pour tube, and an 18mm wrench (or socket/ratchet). Optionally you might also want a shop rag, solvent or carb cleaner, and a tarp/board/creeper to lay on.

 

 

To begin, park your truck on a level surface and crawl underneath the driver's side (below the gas tank), look forward, and spot the transfer case fill and drain plugs:

 

 

 

Once you have located both the fill and drain plugs, place your drain pan under the transfer case, remove the upper (fill) plug, then the lower (drain) plug to relieve the old fluid from the housing.

 

A word here about hardware and metallurgy - the housing of the NVG-149 transfer case is NOT aluminum but rather magnesium; this is critical to know because one cannot use just any hardware with magnesium. Incompatible metals will (over time) corrode each other, the result here will be the eating away of the threads in the magnesium housing - this phenomenon is called galvanic corrosion. YOU MUST USE THE COMPATIBLE OEM PROVIDED HARDWARE. So if you fumble and drop your fill or drain plug into your catch pan, go fishing for it and clean it off with your shop rag, because you need it - no substituting here.

 

After the housing has completely drained, replace the lower (drain) plug and tighten until it is snug; you do not have to "cinch" down the plug, you only need to tighten enough to prevent a leak and that typically only takes "hand tight plus an additional quarter-turn" to accomplish.

 

Leave the drain pan in place and refill the transfer case using your pour tube or gear lube pump. Pour the AutoTrack II fluid into the top (fill) hole until it begins to overflow and the excess run out the hole, then cap off the upper hole with the fill plug. Again tighten with your wrench "hand-tight plus an additional quarter turn".

 

Thoroughly clean the back of the transfer case; you want it spic-and-span to be able to spot leaks later. Use your shop rag with a dab of solvent (any paint thinner) or a shot of spray carburator/brake cleaner to remove all trace of fluid and dirt. If you discover that either your fill or drain plug 'weeps' go ahead and tighten the offending plug with your wrench just enough to arrest the leak.

 

Job Done - remove yourself and your tools from under your truck. Take your truck on a quick errand to fetch your favorite cold beverage from the quick-mart. Park the truck, crawl back underneath and remove the top plug to check the fluid level; if it has dropped top-off the transfer case with AutoTrack II fluid. Replace the fill plug and enjoy your fresh cold beverage.

 

At 7500-mile intervals (every other oil change) remove the upper fill plug and re-check the fluid level in the transfer case; if it has fallen go ahead and top-off with more AutoTrack II fluid. It is also recommended to check fluid levels in the front and rear differentials at the same time.

 

Mr. P.

Edited August 18, 2008 by Mr. P. (see edit history)

[Ron's SS]

Another great How-To, thanks Mr. P

[jchitwo]

Sweet got me another weekend project!

[yeary03SS]

Is it ok for what's left of the residual tranny fluid to mix with auto track II fluid or does it need to drain for a while to get as much as possible out?

[misterp]

Is it ok for what's left of the residual tranny fluid to mix with auto track II fluid or does it need to drain for a while to get as much as possible out?

Just let it drain a few minutes until it stops dripping; it'll be fine from there.

 

Mr. P.

[Loeryder]

I believe the transfer case in the SS is the viscous clutch type, which calls for Dex II ATF, not AutoTrakII.

 

The electronic switchable 4x4/Auto4x4 transfer cases, like that in a Z71 call for ATII.

When I had my Z71 I went around and round with the dealer, and Amsoil trying to find a suitable synthetic. Finally broke down and just ran the GM stuff.

 

In the SS I am running Mobil1 ATF with no problems.

[CoolBlueSS]

I've heard that the Auto-Trak II fluid will quiet a noisy t-case, and will be a smoother operating unit.

[Woffski]

Nice info.....

[CoolBlueSS]

I did it last weekend. It does seem to be quieter.

[FuelSlut]

when i went through my case and replaced the guts... (from the factory) atf poured out of it... and on general motors service information website it reccommended atf... what gives?

[misterp]

when i went through my case and replaced the guts... (from the factory) atf poured out of it... and on general motors service information website it reccommended atf... what gives? 

I've ****-footed around this but will just blurt it out - GM fills the transfer case with ATF at the factory - you can refil with ATF. But AutoTrac II is MUCH better, worth every penny.

 

Mr. P.

[FuelSlut]

exactly what i wanted to hear... thanks a lot mr. P your the man

[kaotik1]

bump

[cerbomark]

Misterp, Thanks for the great info... I did, front, rear and t-case all yesterday. Alot of metalic particles in front diff.. T - case probably had ATF as it was red and the Auto trac II was blue. Still get the same noises though . I only put about 10 miles and maybe it will improve with time??? Just for information, I had 21K miles and the rear fluid looked fine but changed it anyway.

[BenKey]

Synthetic ATF is an acceptable fluid in the transfer case also.