PDA

View Full Version : What kind of fluid do I fill the transfer case with?



Rox
11-20-2011, 08:24 PM
I have a 1982 K-5 Blazer with a NP 208 transfer case.
Do I fill it with normal transmission fluid or is there something else I should
use to fill it with?
Thanks for the help.

junkyard dog
11-20-2011, 08:50 PM
I believe its dextron 3

STIgary
11-20-2011, 09:24 PM
Regular motor oil.

shovelhead77
11-20-2011, 09:31 PM
Regular motor oil.

never heard of anyone useing motor oil in a transfer case

Biggs Chevys
11-20-2011, 09:33 PM
np203 uses 10-40w motor oil...

np205 uses wither atf or gear oil...

np208 uses atf...

shovelhead77
11-20-2011, 09:38 PM
np203 uses 10-40w motor oil...

np205 uses wither atf or gear oil...

np208 uses atf...

learn something every day.
thats why I didn't call him crazy for saying motor oil I didn't know for sure.

NightKrwlr
11-20-2011, 09:41 PM
Regular motor oil.

nope but good guess

STIgary
11-20-2011, 09:53 PM
I didn't realize the 205/208 used something other than what the 203 does. My b

sevenn07
11-21-2011, 03:08 AM
The use of the 205 kinda determines what you use in it from what I've read.
ATF moves around a lot easier but gets hot quicker.
Gear oil moves slower but doesn't heat up as bad.
You just have problems if the tranny atf and t-case gear oil mix.

heavyleft
11-21-2011, 03:20 AM
I have a NP 208 in my 87 and its ATF like Biggs is saying.

STIgary
11-21-2011, 03:26 AM
How would the two mix?

junkyard dog
11-21-2011, 03:32 AM
sometimes people put the wrong kind in....mixing them can cause things like seals to go bad or make it not shift right.... its not good to mix them.... you would have to drain the case flush with fresh fluid if alot was put in and then fill with the proper fluid

84_K5
11-21-2011, 03:45 AM
Mixing meaning there is a seal that separates the trans fluid in the trans and gear oil inside the NP205. If the seal goes bad.. the fluids mix back and forth… ask me how I know.

That is one good reason to put ATF inside of the NP205… if the seal fails and fluid mixes.. no big deal. But as stated before, the gear oil will be cooler and offer better protection. I run royal purple gear oil in my 205 now that the seal is fixed.

junkyard dog
11-21-2011, 03:50 AM
ok sorry ... been a long day

sevenn07
11-21-2011, 04:02 AM
Mixing meaning there is a seal that separates the trans fluid in the trans and gear oil inside the NP205. If the seal goes bad.. the fluids mix back and forth… ask me how I know.

That is one good reason to put ATF inside of the NP205… if the seal fails and fluid mixes.. no big deal. But as stated before, the gear oil will be cooler and offer better protection. I run royal purple gear oil in my 205 now that the seal is fixed.

He got it right on the money!

STIgary
11-21-2011, 05:27 AM
So, is the 203 not really capable of leaking? I ask because you really singled out the 205. You've got me questioning if I should drain my 203 and put in ATF.

trav0302
11-21-2011, 12:05 PM
It feels like dumb question time! YAAAAAHHHH

I have not done this or will i ever but in theroy could power steering fluid work?





Lets see if anyone remembers this.:music-smiley-006:
One of these things is not like the other. :icon_kidra:
One of these things just don't belong.
Can you tell which thing is not like the other.
By the time i finshish this song?:rockon_smiley345:

84_K5
11-21-2011, 02:42 PM
203 requires ATF. 205 - can take either ATF or Gear Oil..... if your seals are good in the 205 - use gear oil

Biggs Chevys
11-21-2011, 03:14 PM
203 requires ATF.


no, a np203 requires 10-40w motor oil....

84_K5
11-21-2011, 03:45 PM
my bad.. I ment the 208

Biggs Chevys
11-21-2011, 03:57 PM
So, is the 203 not really capable of leaking? I ask because you really singled out the 205. You've got me questioning if I should drain my 203 and put in ATF.

he singled out the 205 because that is what he has and what he has had experiences with....

yes the np203 can leak.... only run the 203 with 10-40w oil....

sevenn07
11-21-2011, 09:55 PM
The 205 is the only one that can run both ways. although I would suggest gear oil, ATF has worked for others.

70-K5
11-21-2011, 10:13 PM
And here I thought that the 205's only liked gear oil...
Anybody have the detailed explanation of why each case takes what it does?

sevenn07
11-21-2011, 10:17 PM
And here I thought that the 205's only liked gear oil...
Anybody have the detailed explanation of why each case takes what it does?

As for the 205s, I'd say they do prefer gear oil.
ATF has supposedly burned some up, but that's a I think that is what caused the problem.
Gear oil is recommended but if mixing occurs with the tranny, it causes problems.
So if you put ATF in and it mixes, not such a big deal.
I think that is the reason behind some running ATF in them.

As for 208s, they are chain driven which is very different.
That's why they use or were designed for ATF (as well as the 241)

203s, no clue at this point but I'll see what I can't find.

84_K5
11-21-2011, 10:22 PM
GM did say to put ATF in the later NP205's toward the end of production - my understanding is this change was to help with fuel mileage....that's it. Not sure how much better your actual mileage could be though….

sevenn07
11-21-2011, 10:22 PM
203 needs thinner oil than gear oil due to the magnitude of individual roller bearings needing lubrication.

70-K5
11-21-2011, 11:32 PM
As for the 205s, I'd say they do prefer gear oil.
ATF has supposedly burned some up, but that's a I think that is what caused the problem.
Gear oil is recommended but if mixing occurs with the tranny, it causes problems.
So if you put ATF in and it mixes, not such a big deal.
I think that is the reason behind some running ATF in them.

As for 208s, they are chain driven which is very different.
That's why they use or were designed for ATF (as well as the 241)

203s, no clue at this point but I'll see what I can't find.

Ok, so you didn't get the question... The above has already been stated at least twice in the thread.

What is the reason gear oil was used in a NP205? Why is it okay to use ATF instead of gear oil? I'm wondering about the science behind how the gear oil works inside the transfer case.

Same thing on the NP203, stuff like the way the internals are designed so that 10-40 or SAE30 works to lubricate well.

Obviously the chain drive of the NP208's and NP241C's require a different lubricant but why...

Because now I'm thinking that if you can replace gear oil with ATF then why couldn't you run ATF in your differentials?

sevenn07
11-22-2011, 01:45 AM
I answered the 203. Can't run gear oil due to the numerous bearings needing lubrication but something more viscous than ATF for the higher lubricity.

The 205 is not really meant to run on ATF. Over the years GM went from gear oil, to motor oil, to ATF. It has gears which meet tooth on tooth which creates more friction needing a higher ability to lubricate the meeting surfaces.

208s and 241s are chain driven. Due to the chain, it spreads out the contacting surfaces to many contacting surfaces, thus you get less heat and less need for more viscous oil.

I'd say you can run ATF in you diffs but do you want to decrease there life? Same reason you try and keep your tranny cooler and increase it's life.
The way I see it, keep it as cool as you can with every part still getting the proper amount of lubrication.

muddyK5
11-22-2011, 07:19 AM
Gene, 7 is mostly right. Atf is thinner and seeps into the needle bearings. Lubes the chain, the friction clutches would be the key factor.
With the oil use. Oil takes shock loads better, clings better.
Now you can add zinc additives to the motor/gear oil to prolong life, wear and tear. From what I was told long ago.

I did use a zinc lithium grease in a dodge colt vista after finding the bungholes at the oil shop loosened it. I was there in wilsonvile getting pc stuff at Fry's. Came out to a pool of gear oil.
I drove that p.o.s. for a quite few years after that. Never could figure out how to get oil in it. I used the grease gun on the vent tube. Lol.

Biggs Chevys
11-22-2011, 04:06 PM
np 203 using oil i believe has to do with the carrier that makes it a full time 4wd...

np 205 went to atf for fuel economy.... never heard of a np 205 with motor oil....

atf in your diff.... are you nucking futs?
ever see how foamy atf can get? think about how much your axles "rattle" down the road.... foamy/aerated fluids will not lubricate your gears....

Tincan86
12-14-2011, 08:16 PM
How would I know what tc I have and how would I go about draining and refilling it? I am looking to replace all fluids in the truck since it sat so long

NightKrwlr
12-14-2011, 08:34 PM
How would I know what tc I have and how would I go about draining and refilling it? I am looking to replace all fluids in the truck since it sat so long

all of the transfer cases have a drain plug and a fill plug. if it is aluminum with a rear slip yoke it is a np208 or np241 (both of these take ATF). if cast iron it is an np203 or np205. np203s have a large aluminum tail-cone/ speedometer housing on the back of them and are full time 4wd and have a fixed rear yoke. np205s are identifyable by the round plate in the middle of the back side with 3 bolts in it, and can be either slip yoke or fixed yoke.


if the truck is stock (if you are sure) , you can tell us the year, and we will tell you what you have.
google search and compare the pictures on google to your transfer case.
or post a picture and we can ID it.

Tincan86
12-14-2011, 09:21 PM
It is an 86 I will try to get a pic tonight

70-K5
12-14-2011, 09:32 PM
i'd bet you have a NP208. And Brent, I don't think the NP203's have a drain plug.

http://i948.photobucket.com/albums/ad329/c-code71/np208flatcrossmember_rear2.jpg

NightKrwlr
12-14-2011, 10:00 PM
i'd bet you have a NP208. And Brent, I don't think the NP203's have a drain plug.


whatever theyre worthless anyway. lol. how do you drain them, then?

70-K5
12-14-2011, 10:21 PM
You just take them out and leave em on the side of the road!

sevenn07
12-14-2011, 11:13 PM
You just take them out and leave em on the side of the road!

lol i chuckled.

Tincan86
12-19-2011, 08:42 PM
70-K5 That is what mine looks like, however mine isnt that clean . Looks like I need to get a pump to pump fluid in it when I drain it

70-K5
12-19-2011, 08:56 PM
Yea, they aren't always that clean.

I got a cheap pump at an autoparts store for a few bucks. It screws onto the bottles of trans-fluid and is the only way I know of to get fluid in there. (except for cutting a hole in the floor.)