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'78 owners manual says conventional 4wd takes 80w gear lube, and full time 4wd takes 10w30 or 10w40. That's whats confusing me. I agree with you Mike, gear lube seems like the obvious choice. I just don't want to put gear lube in and have it not get lubricated right. Will I hurt anything if I put in gear lube?
What?!! Who ever heard of motor oil in the x-fer case. Thats is definately news to me.. I cant see why though? np203 has a differential and is chain driven but thats the only difference that I know of.. nothing different than the inside of a rear end which uses gear oil.. now this has got me thinking.. I SHALL find an answer.
btw, fwiw, I know someone with a 1/2ton part-time 4x4 with a np205 case, factory. (its all got a manual gear box)
What year is his truck? They started using the 203 around 77, and with the 4 sp in front of it, I think most were 205 behind it. Most if not all auto's in 1/2 tons and ld 3/4 tons were the 203. The new t cases take dextron, and I have an 88 f-150 with the 5 sp and that is integral with the t case and they share auto tranny fluid as a lube.
If the manual says 10-30 in the 203 then thats what it needs I guess.
Mike, the chain is what makes the difference I assume, along with the internal differential. I think it was the differential clutches that need the lighter lube, not sure though. Putting 80w-90 in the NP 203 won't hurt it. I put it in mine when I converted it to part time. It did have 10w-40 in it before.
As far as
"btw, fwiw, I know someone with a 1/2ton part-time 4x4 with a np205 case, factory. (its all got a manual gear box)"
The 205 was used with all manual gear boxes. The NP 203 was used with all auto trans 1/2 & 3/4 ton trucks, including the HD 3/4 ton models. My 77, came with a 400 HD emiss. motor, TH 400, and the NP 203 in it. It's all on the RPO decal in the glove box, so I know it's original. It was the heaviest 3/4 ton you could get in 77, at 8,400 GWVR.
The NP 203 was first used in 1974 models. It was used until 1979. All 1980 trucks had the NP 205. In 1981, it was a transition year, and some had the NP 205, while some got the new NP 208 that came out officially in 82. From 82 - 87, all auto's had the NP 208, and 1/2 & 3/4 ton manuals had the NP 208 as well. Only the 1 ton models had the NP 205, behind the manual, and behind the TH 400.
Thanks for your help guys. I'm learning that I still have SO much to learn. My '78 K10 is my first 4wd and I've only had it a year. This is also going to be my 2nd year of plowing. To say that I have learned alot through reading these forums is an understatement. Don't want to get too far off the subject, just wanted to say thanks.