NP203 question
 

I just found out my truck has an NP203 transfercase on it. From what I have read so far online this is a full-time 4wd setup. My truck has manual locking hubs on it, and it sounds like that isnt normal unless it has a part time conversion in it. The hubs that it has are superwinch and they look like they have been there a long time.

Would it be better with the part time kit or as full time?
What are the advantages of full time and part time 4wd?
Should I take off the manual hubs and replace them if it still has the full time setup?
Thanks

Re: NP203 question
 

Unless you are rock crawling or full time off road you do not need full time 4x4 unless you want to burn a lot of gas.

Re: NP203 question
 

If it has part time conversion and you put in full time "plugs" (can't think of term they aren't really hubs) you will destroy the transfer case or something else. I think if you turn the hubs free and do NOT have a full time kit all that happens is the front drive line turns and you do not move. If you have the hubs turned to lock and DO have a part time conversion you have been very lucky driving on pavement.

Re: NP203 question
 

As unpopular as the 203’s were (outside of 203/205 doublers) it would be very odd that an 1987 K20 would have a swapped in a TH350 and NP203. Are you sure it isn’t a NP208? Is the case aluminum or cast iron?

Re: NP203 question
 

I belive 1980 was the last year of the 203.

the 205 was used 1968/9 - 1991. I think the 208 was from 1981 - 1991.

the dates are aproximate, I am pulling this out of my head, not a reference.

Re: NP203 question
 

Oh, and the 203 does not like being in 2wd mode, even with the part time kit, it still will slowly destroy its self.

If you have a 203, I strongly sugjest you aqqire a 205 and do a doubler.

Re: NP203 question
 

1979 was the last year for the NP203... All 1980 GMs used the NP205

Re: NP203 question
 

Thats right, 80 was kind of a goofy year too for them, with the rounded fenders, but having the square headlights.

Re: NP203 question
 

I thought it said 203 on the transfercase and it looks exactly like a 203, not so much a 208 tho and not at all like a 205. What first got my attenion was how to drain it since it only has one plug in the middle. The plate on the floor says
Low Lock
Low
Neutral
High
High Lock

So I should just junk it and get a 205?
How do you do a doubler and whats the point of it?

Re: NP203 question
 

I'd pull the range box off and save it, as well as look for a 205. Doubler is easy, it just costs $$$.

Re: NP203 question
 

Money is a problem right now. Would it be easier and cheaper to just put in a 205? What is the range box?
Im new to transfer cases so I dont know to much. What does the doubler do?

Re: NP203 question
 

A doubler takes the gear box off of the 203, this box has a either direct 1:1 drive, or a 2:1 low range.

If you set it up as a doubler, it means that with the 1.96:1 low range of the NP205 you will have almost a 4:1 low range.

Re: NP203 question
 

Guess that 85K I put on mine over 15 years was waste of a good rebuild! Checked out the inside and its still good to go so it went back in. I've got a Doug Nash shaft kit that makes it a true in-out box.

Re: NP203 question
 

The 203 is fine for most everybody that doesn't crawl rocks and try to self destruct their trucks. Nothing wrong with that if you do, I'm just sayin...

The 203 with the part-time kit AND manual hubs will last 99% of users just as long as a 205 will.

Re: NP203 question
 

throw it in 4hi every fill up for a few miles and you would be fine with that old conversion. With the new conversion it allows the shaft to pump oil to the rear output bearing. It is a very strong case and can give you plenty of reliable service through the years and only requires simple motor oil for its lubrication. If it ever tanks then is time for a transfer case swap. But a running 203 is nothing to be ashamed of. The only time people break them is when they dont use 4hi every 500 miles to pump the oil, and even then it is normally the output bearings that blow.

Re: NP203 question
 

If the 203 isn't giving you any trouble I wouldn't replace unless you are spending a lot of time off road or putting a lot of torque through it. I think it is recommended that a 203 that has been converted to part time be put in 4wd every so often for lubrication purposes. Can someone confirm this?

Re: NP203 question
 

scooter122983,

I didn't see your reply until after I posted mine. I guess you confirmed what I had heard.

Re: NP203 question
 

Im not sure if it has the conversion kit in it. Im going to be draining it tomarow.

I should use motor oil? I already bought atf for it, thats what I was told by a few people to put in it. What is the best thing for it?

Is there any way to tell while I am draining it if it has the coversion or not?

This truck has been pieced together over the years so I have no idea what it has done to it and im trying to get a good idea as to whats in it.

Re: NP203 question
 

That is just not so....Converted NP203s can and will last for many years. I have personally installed many dozens of these kits and never had a failure.




Yes^^^

Re: NP203 question
 

Having experince with them you all probably know better than I do. My information is based off an article I read in four wheeler a few years back, the article stated that when setting up the 203 as a part time that the inner differential was prone to grenading because for what ever reason it did not like having the front shaft not spinning.

Or now that I think about it perhaps it was the reason you should not run locking hubs with out the adapter kit.

I cant remember.

I have had 3 of them, they all 3 came behind TH350's and when the TH350 grenaded, I yanked em and installed a SM465/NP205. Anyone who likes to play off road knows that it doesnt take much to roasty toasty a TH350.

Much of my bias comes from my bad experinces with chain driven transfer cases. I could build a road block with all the NP208's I have grenaded.

And such is why I am a fan of the 203/205 doubler, its all gear driven, no chain to mess with, and its a pretty stout setup.