As per this thread I see that my T-18 takes either straight 50w oil 80w-90 gear oil (which is it guys?) and my NP208 takes ATF (what kind, Type F or one of the thin GM crap?).

After wheelin' and turning my truck into a submarine I replaced all the fluid in the truck. I reaplced both differentials, the transfer case, and the tranny with 80w-90 gear oil. I assumed that was what it took. Some sort of oil came out of both the tranny and transfer case. It was thick and nastified (all green and water contaminated). Definitely was not ATF that came out of the NP208. Of course that does'nt mean some previous owner hadn't thought like me adn just run regular gear oil.

So, what fluids do the transmission and transfer case actually take and can any harm be done by running 80w-90 gear oil in them instead? I have beat on the truck pretty hard since then, both on adn off road.

 

80w-90 gear oil in the T18
dextron ATF in the np208 , and yes its the thin GM crap, that isn't any thinner than type F. there are no clutches in the 208 so no need for the friction additives.

gear oil will kill a np208 (and a BW1345/1356) real fast because it wont flow through the chain.

 

Okay, I will leave the 80w-90 in the T-18. Tomorrow I'll change the gear oil in the NP208 to ATF. What type of Dexron does it take? I believe there are 5 different versions of the GM ATF. Does it even matter what type of ATF I put in there?

Looks like I'll have some more oil to burn in my waste oil heater tomorrow. Should keep me warm while I change the fluid!

 

dex-I, dex-II, dex-III, they are all backwardly compatable

 

Just about everyone uses the GM "crap" these days. Tcase shifted to ATF fluid in about 1980 after tha energy crunch and they went from a HD 200 LB NP205 to a 80 lb aluminum one with low drag bearings and reduced clearances that the dextron works fine in. Also, You might use 75w90 dino oil in T18 as it will make fore a lot easier shifting in cold weather.

 

You mention the NP205 being changed in ~1980. Is it the same with the NP208 or maybe those transfer cases basically identical (my truck has an NP208)?

In any case, I'm gonna run out now and get some GM ATF to put in the NP208 and I think I'll pick up some 75w-90 gear oil as you suggest. The past few days since it's been real cold out it seems like what little is left of my synchros in the T-18 are either gone or not working. I gotta double clutch every shift and be dead-on or it won't go into gear. At least the synchros aren't letting it grind. heh heh

 

definitly get some at fin the 208, when i was 15 i put gear oil in the 208 in my 85 ford and it destroyed the insides of the t-case..i had no idea why it happened.

 

The 205 is different then the 208. The 205 has a cast iron case so the gear oil will be fine. The 208 had an aluminum or magnesium case therefore requiring the ATF. Theoretically the organic gear oil will have a reaction with the non ferrous case of the 208.