1977 NP203 info

[codyC10kid]

I,v been doing alot of Reading about the NP203 transfercase.The parts guy told me to use gear oil,so that's whats in it now (i guise i need motor oil???)i only put about 100 miles under 45 mph so i don't think i did any damage (i hope)...I'm coming to YOU guys,I'm going to replace all the fluid when i put my new motor in. So lets start at the Front diff...

GM 10 bolt what fluid...(gear oil?)
GM 12 bolt what fluid...(gear oil?)
TH350 tranny what fluid...(Dex/Mec 3?)
NP203 Transfercase what fluid...(...)it is a full time 4x4,also is it a gear to gear OR is it chain...
OH almost forgot...The Differentials Should i use Synthetic oil or no
I hope some body can set me straight on the right path,besides that parts guy behind the counter 

[werewolfx13]

the 203 is a heavy duty chain drive transfer case that uses 10w40 motor oil. TH350 should be dex/merc 3 or equivalent.

[codyC10kid]

the 203 is a heavy duty chain drive transfer case that uses 10w40 motor oil. TH350 should be dex/merc 3 or equivalent.

thanks for the info helps me alot

[Blazin]

As far as synthetic in any of your driveline its up to you. It is more expensive, it does make things run a little cooler. Good for hot climates like south west. It is also doesn't get quite so thick in the extreme cold after sitting for several hours. Parts life is extended with it no doubt.
Front and rear diffs you could use 80/90 gear oil, or 75/140 synthetic gear oil.
TH 350 Should be dex / merc III.
NP 203 either motor oil, or synthetic motor oil, 10/40, or 10/30. Have also seen 80/90 gear oil, and  75/140 synthetic gear oil used in them with no problems.

[codyC10kid]

thanks for the info,ill be chainging the fluid soon