Transfer case fluid - 1991 GMC K1500

Too thick of fluid will not circulate and will burn up your transfer case. you definitly need to use the manufacturer recommended fluid.

If the transmission is automatic then transfer case takes automatic Dexron fluid. If it is a manual transmission then transfer case takes engine oil.

Transfer Case
NVG 236 and 246 Auto-Trak II Fluid Gm P/N 12378508 NVG 261 and 263 Manual Transmission Fluid GM P/N 88861800

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.

The two units do not share or mix fluids. The transmission needs automatic transmission fluid and the transfer case uses ONLY Auto-Trak II fluid (only available at GM dealer). Do not put any other fluid in either.

Transfer case fluid is different from the trans fluid, transfer case takes a Blue fluid made by G.M. can't think of the name of it, and trans takes Dex III or IIII read manual, if it is getting to transfer case then you deal between the trans and transfer case is bad causing it to **** the fluid out of trans, need to change the seals this time. Car Quest sells a 1 piece seal that seals both units instead of 2 different seals. Good Luck

Transfer case fluid is a GM AutoTrak II fluid, use only this in the transfer case. For front and rear differential use a good quality gear lube 75W-95.

if it is an electric shift t-case gm has there own oil not found at auto part stores

They run on the same fluid but have different fill ports. The transfer case has a fill hole on the back of the case. The fill plug is a big looking nut. Fill the case from there on a level ground until the fluid starts to come out, then it's full.

On the backside of the transfer case,as it sits in the vehicle.The plugs will be facing the rear differential.The one down low is the drain,while the top one is fill,of course.The fluid recommended is automatic transmission fluid,Dexron,and the transfer case is full when the fluid is at the bottom of the fill hole.