Questions about my transfer case

[jumpkickyergunt]

I have a 79 k10 with an np203. It's got manual locking hubs. It drives in hi so does that mean it was converted to a part time case?  I'm going to change the oil so do I stick with 10w30? Also, what is the capacity of the 203? Thanks

[rich weyand]

1) Yes.  As the NP203 was designed for full-time use, it has no internal oil pump.  The chain drive throws enough oil to keep the reservoir above the rear output shaft bearing lubricated.  Driving it hubs unlocked in HI all the time will run the bearing dry and burn it up.  Replacing it is not pleasant.  To avoid this repair, put the NP203 in HI LOC for the first couple miles you drive every day, or every gas stop when driving long distances.  If the hubs are locked (such as in the winter), there is no need to do this, as the chain is being spun from the other end.

2) Spec is to use engine oil, which is 10W30. 

3) Service manual says approximately 7 pints, to within 1/2" of the filler hole.  Most people fill to the filler hole, and some claim it takes as much as five quarts.

[jumpkickyergunt]

Thank you. So what's the difference between hi and hi loc in this set up?

[Magic1]

Best I can remember with the way mine was, being converted; high=2wd highway or normal driving, hi lock=4wd high, lo=2wd low range for say pulling, lol loc=same as low except for 4wd. Hope that makes sense and I'm not telling you wrong.

[Irish_Alley]

think of the 203 like a differential. "Loc" will lock the front and rear drive shafts together so both front and rear axles have power. almost like a locker in a rear how it catches posi. then in the "unlocked" the wheels with the least resistance get all the power so if your front tire is in mud it will get all the power and spin and will be the only tire to spin, as in a open differential and only one wheel spinning

[rich weyand]

think of the 203 like a differential. "Loc" will lock the front and rear drive shafts together so both front and rear axles have power. almost like a locker in a rear how it catches posi. then in the "unlocked" the wheels with the least resistance get all the power so if your front tire is in mud it will get all the power and spin and will be the only tire to spin, as in a open differential and only one wheel spinning

That's the way the stock one works, with the differential still in it.  Your modified one works differently.

HI and LO are 2WD only, in either HI range (1:1) or LO (2:1).  So if you have 3.73:1 axles, in HI it will be 3.73:1 and in low the combination will be 7.46:1.  If the hubs are FREE, the NP203 chain drive, the front driveshaft, and the differential will not turn.  If the hubs are in LOCK (which you might do in winter, so you can engage 4WD without getting out to lock hubs), the NP203 chain drive, the front driveshaft, and the differential will all turn, as they are being driven by the wheels.  This will also oil the NP203 rear output shaft bearing.

HI LOC and LO LOC are the same ratios, except now the front driveshaft is driven from the transfer case.  If the hubs are FREE, then it is still 2WD, but you are spinning the extra hardware, including the chain drive inside the NP203, the front driveshaft, and the differential, including the half-shafts and U-joints to the hubs.  This is important to do once in a while (first couple miles every day) to keep the NP203 rear output shaft bearing oiled.  If the hubs are in LOCK, then you are in 4WD.

BTW, with the hubs in FREE, if you start out in HI LOC to fill the oil reservoir over the rear output shaft bearing, you have to shift from HI to HI LOC while stopped.  You can shift from HI LOC to HI while driving, so after the first couple miles you just do the shift without stopping.

[Irish_Alley]

i dont know if im not thinking right or just not reading it right but i thought the only difference in the modified and stock 203 is the "hi" in high is 2wd while the "lo" unlocked is still the 4wd

[jumpkickyergunt]

Thank you everyone for the explanations. My application is like how Rich described it.

[rich weyand]

i dont know if im not thinking right or just not reading it right but i thought the only difference in the modified and stock 203 is the "hi" in high is 2wd while the "lo" unlocked is still the 4wd

No.  Unmodified, the HI and LO positions, the front and rear axles are differential-connected (called "full-time AWD"), and in the HI LOC and LO LOC positions, the front and rear axles are locked to each other through the transfer case, like a locking rear diff when the wheels start to slip.

Modified, the differential is removed.  So the HI and LO positions are 2WD only.  The HI LOC and LO LOC work the same as unmodified, the front and rear axles are locked to each other through the transfer case, so in this case you have 4WD (assuming the hubs are in LOCK).