Oil Type for 4X4 transfer case-78
 

I have a 3/4 ton 4X4 78 Chevy truck that has the original driveline, 400 small block, 400 tranny etc. I'm not sure what type transfer case it has, but it is a full time 4 wheel drive (no lockouts).
Reading the owner's manual it says 80w90 for part time and 10W30 or 10W40 for full time transfer case.
I'm confused and sure don't want to put the wrong weight oil in it. Any insight on this? Thanks, Lane.

Re: Oil Type for 4X4 transfer case-78
 

Does your shifter say Hi Loc, HI, N, Lo, Lo Loc? If so it is the full time 203 case.

If the shifter says 4H, 2H, N, 4Lo, it is the Np 205. I highly doubt it has the 205, as those were reserved for the true 1 tons and manual transmissions.

So 10w 40 is fine for the NP203.

If you want any more info, check near the front drive shaft somewhere, should be either a round tag or rectangle one saying "New Process Gear" with a model number.

Re: Oil Type for 4X4 transfer case-78
 

http://www.chuckschevytruckpages.com/drivetrains.html This might help for identification.

If you want to know the oil, try the "smell" test. If it's 90w in there now it will be like "bad" milk. You won't wonder about the smell, it will kinda smack you in the face, lol. (you'll definitely be able to tell the difference) From what you've posted, it "should" be 10w-30, or 40.

Re: Oil Type for 4X4 transfer case-78
 

I put straight non-detergent 30weight in mine just the other day.

Re: Oil Type for 4X4 transfer case-78
 

Thanks to the great advice on this thread (and the links provided), I discovered my transfer case is a full time NP 203 case. I added 10W40 motor oil. Appreciate the help. Lane.