NP203 Full Time to Part Time Conversion

[septantrionalis]

I own a 1974 Chevy K10.  My truck has a stock NP203 transfer case.  I had a question regarding the 4 wheel drive.  I assume the shift pattern is: LO(Loc), LO, N, HI, HI(Loc).   LO(Loc) and HI(Loc) engages all 4 wheels?  LO and HI is just two wheels?  Why do people say that its full time 4 wheel drive then?

I ended up having a shop add a set of locking hubs to the front wheels.  They also did a full time to part time transfer case conversion.  What exactly did this change?  I assume the shift pattern is still the same - LO(Loc), LO, N, HI, HI(Loc)?

[David A Young]

Np 203 pattern will be low loc low neutral high lock and high. A part time conversion will make high 2 high instead of 4 hi which is the gear it runs in on the road all the time.

[Irish_Alley]

to add to what david said when ever youre in lo or hi (before the part time kit) the transfer case was pretty much like an open differential. if the front tires had more traction than the rear the rear tires would spin unless you put it in loc then it would lock the front and rear diffs together and give them the same amount of power

[septantrionalis]

Awesome, thanks for the replies!  Irish_Alley, that was exactly what I was looking for regarding the part time conversion.

[big_al273]

Don't forget that with the part time conversion done you need to run the case in 4x4 every so often for proper lubrication of everything inside, i would tell you exactly how often but i don't remember as it isn't info i need.

[Irish_Alley]

think most recommend once a month for a few miles

[rich weyand]

Don't forget that with the part time conversion done you need to run the case in 4x4 every so often for proper lubrication of everything inside, i would tell you exactly how often but i don't remember as it isn't info i need.

I put my modded NP203 in HI LOC for the first couple of miles every day, then shift out of HI LOC to HI while rolling.  Yeah, you don't need to do it every day, but you don't want to forget to do it once in a while, and this is just easier.  If I am on a trip racking up miles, I put it in HI LOC for the first couple miles after every gas stop.  This is to fill the little oil reservoir on the rear output shaft bearing.  Since it was designed to be full-time 4WD, there is no oil pump in the NP203.  The drive chain to the front wheels flings oil inside the case, which runs down oilways cast into the case, to the reservoir for the rear output shaft bearing.

You don't need to do this if the front hubs are in LOCK, such as in the winter when you lock the hubs before leaving home so you have 4WD available if you need it.  Then the chain is being spun from the front wheels, so you get the oil fling you need.

[Austin4wd]

I had a '75 K5 with full-time. How I got around it was I yanked a TH350/NP205 combo from a '78 K10 and pulled the front diff out too. Played a game of musical parts and boom! Part-time 4x4 K5