Lubrication

[fnny6770]

My 1980 GMC K3500 has a 454 with the standard 4-speed transmission, it came from the factory with the 400 engine and the th400 transmission, my question is what kind of lubricating fluid should be in the transfer case?
When my brother put the four-speed transmission in I'm guessing he had to put in the transfer case out of his truck along with the engine because automatics and standards don't necessarily line up or interchange?
But I noticed the rear seal on the transfer case is leaking a little now and it appears to be transmission fluid for an automatic transmission as far as I can tell, it is reddish in color and thin, I don't know for sure which transfer case it is I don't know how to tell the difference maybe someone can shed some light on this?

 

[idahovette]

Is the transfer case aluminum or iron?

 

[Terlingueno]

My 85 K20 has an NP208 T-case, ATF is what fills it

Finding out which T-case you have will help answer, look on the T-case there should be a round metal ID tag

 

[fnny6770]

I will have to look for the tag because I don't know which one it is, just for memory I think it looks like steel or cast not aluminum, the engine my brother took out of his 78 3/4 ton along with this manual transmission so I'm assuming he brought the transfer case with it but I will look and get back to you

 

[fnny6770]

I could not find around metal tag but I did take a few pictures and one of them has a number in it

 

[fnny6770]

These pictures here of the transfer case

 

[PrairieDrifter]

These pictures here of the transfer case

That's an np205. It takes 80-90 gear oil.

 

[PrairieDrifter]

The tag on those is on the front of the case under the shift rails.

 

[fnny6770]

I found the tag and it appears to be damaged a little but I believe 205 is legible

 

[Grit dog]

That's an np205. It takes 80-90 gear oil.

Yup. Except the mfgs recommendation for the 205 changed around 1980s to ATF.
It’s gear drive so I’d prefer the “cushion” of a higher viscosity oil however to my knowledge it would likely perform ok with any reasonable lube.
Not unlike many v drives and d drives in boats. Back in the day, gear oil was recommended, then went to ATF and many back to engine oil as lube. Our last boat was one of those that came factory filled with atf and then the recommendation changed to using 15-40.

 

[fnny6770]

I'm all for using gear oil too unless there's something that transfer case that requires a thinner viscosity to keep it in good working order?

 

[Grit dog]

No, dump some gear lube in it and carry on. It’s fine.

 

[fnny6770]

Thank you for everyone's help!

 

[Fat 454]

bananas and saw dust - worked for the "cabbies" every time ....

 

[idahovette]

Never tried the sawdust......but I did use the bananas............didn't seem to work?