converting from part to full time 4wd

GMC4x4

Junior Member
Location
new england
stupid question.. in order to convert from an np208 equipped part time 4wd system to either a 203 or 205 full time 4wd would you need to replace the entire front axle? i assume you would need more than just new hubs. as you can probably tell i'm pretty ignorant about differentials and gears and other such things.

Greg
 

MTCK

Senior Member
Location
Fairbanks AK
No stupid questions, just stupid answers, this may be one of them :) I can't answer your question specifically, but first I will say, the NP203 case is a full time one, and NP205 is a part time like your 208, but stronger and with not as low low-range. I assume that you want to run the truck in full time 4 wheel drive (since you're switching) so you might want to consider replacing your front hubs with the solid ones that the 203 trucks came standard with. Is your truck a half ton? 10 bolt front? If so, you should be able to use a drive shaft from a late 70's truck that came with the 203 and 10 bolt up front. I don't know if your stock shaft will work, but if not, this should. You're going to loose a bit of gas mileage going to this swap. Hope this helps..

MT
 
OP
G

GMC4x4

Junior Member
Location
new england
the 205 is part-time? i must be losing my mind.
i should have given more info, my truck is an 84 GMC 3/4 ton it has a dana 44 in the front with 8 lug hubs, it also has a 350 and granny 4-speed.
i figured solid hubs would be good idea, what i'm not so clear about is i'm pretty sure there is some type of differential up there (in the full-time models) so you can drive around on dry pavement, but i'm not sure if that can be added to my axle or if an entire swap would be required.

Greg
 

MTCK

Senior Member
Location
Fairbanks AK
The NP203 transfer case actually has a differential in it. Then the output from your transmission is actually split 3 times, at the t-case, and one at each axle. I'm not 100% positive, but I don't believe the 203 was ever offered with the 4-speed manual, maybe one of the members with an older pickup can help me with this one, so, some sort of adapter from the transmission to the transfer case may be necessary. Advanced Adapters may be able to help with that one. www.advanceadapters.com I think.

MT
 
OP
G

GMC4x4

Junior Member
Location
new england
thanks for all the help so far MT, but what I'm still not understanding is whether or not there is a differential needed in the front axle that my truck does not have. the way i understand it, the full-time trucks have a diff in the front axle that allows them to make turns on dry pavement without binding up. and the reason you shouldn't drive a truck like mine in 4wd on dry pavement is because it lacks that diff in the front axle, or maybe it has a different kind of differential, this is where i get lost. as far as the t-case itself i'm not too concerned what is in there because i would simply bolt a complete working case to my truck (perhaps w/the help of an adaptor kit). so all i'm really wondering about is whether i would need to add/replace a diff in the front axle or if the entire axle itself is different and would therefore need to be replaced.

Greg
 

plowjockey

PlowSite.com Sponsor
Location
Dayton, Ohio USA
Actually you do not have too much problem with the front diff locked on dry pavement, as long as you are NOT in 4wd. I frequently leave mine locked in inclement weather in case I need to go to 4wd quickly which means that I drive on dry roads some. It only seems to bind if I am in 4wd or if I turn extremely tight.

Bruce
 

MTCK

Senior Member
Location
Fairbanks AK
It is my understanding that the 203 equiped trucks had the same front end as the part time trucks. Your truck is already equiped with an open differential in the front end. Then binding up that you feel in 4 wheel drive when using a part time case comes from the inability of the transfer case to differentiate between the different speeds that the front and rear axle assemblys need to turn on a corner. I also looked, and they did make a 203 that hooked right up to a SM465 transmission, so you should be OK there. So in a nut shell, nope, you won't need a whole new front end. Just out of curiosity, why are you switching to a full time case? Good luck with the project

MT
 
OP
G

GMC4x4

Junior Member
Location
new england
Actually you do not have too much problem with the front diff locked on dry pavement, as long as you are NOT in 4wd.

I'm assuming this means the hubs are locked but the shift lever is still in 2wd, correct?

Then binding up that you feel in 4 wheel drive when using a part time case comes from the inability of the transfer case to differentiate between the different speeds that the front and rear axle assemblys need to turn on a corner.

now this is starting to clear things up, i thought the bind-up was from the difference between the front two wheels in a corner.
so it seems all i would really need to replace then is the hubs and the t-case itself.

Greg
 
OP
G

GMC4x4

Junior Member
Location
new england
Just out of curiosity, why are you switching to a full time case?

well, it's just a thought right now and i wanted to get an idea of what it might entail should i decide to go ahead with it. reason i'm even thinking about it is partly because i was thinking (mistakenly, it turns out) that the so-called bullet-proof 205 was a full time case. but also because my tranny will somewhat soon be in need of rebuilding and i've got fluid leaking out every place you could imagine from the tranny and t-case, so i figure the t-case could probably use a rebuild while everything is apart under there. then i figure, if i need to rebuild this t-case, why not replace it with the stronger one? also in the next year or two i'll be moving to Vermont where i'll likely be encountering just as much dirt road as paved, not to mention the snow, so it would simply be more convenient to be in 4wd mode all the time.

sorry for the long windedness , but thats the answer
Greg
 

reallyrusty

Member
Location
massachusetts
Just my two cents ----- Go with the part time case.
1. It is easier on the front driveline (wear)
2. It will give you better gas mileage.
3. The units are very easy to rebuild, reliable and proven.
and If you get stuck on a snow covered vermont road i would rather be in 2 wheel so i still have the hope of getting myself out
If you get stuck in 4 wheel --- your stuck.
Just an opinion.

I have the 203 converted to part time in my truck and the only thing better would be a 205
 

TLS

PlowSite.com Addict
GMC4x4

My advice...stick with what you have! Get some input and output seals for your particular 4sp/208 combo. If you physically have parts damage inside the transfercase, you may want to have a trans shop or your local GMC dealer rebuild it for you. Because, if you are confused with the workings of a fulltime VS parttime basic setup, your in for a real surprise doing the actual wrenching here! This IS rocket science!

I have a 203 and while P/T 4wd is nice (especially for plowing when its not too deep!) its not that good for milage and pulling out around a corner on dry pavement. You'll think the steering wheel is gonna break your arms!

If you want bullet proof, go with the 205. But like I said, you have a pretty stout setup right now with the 3/4 ton and a 4spd. Your going to be opening a can of worms with switching things around. Just keep it simple.



Get the drips stopped
 

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