How to shift np203 transfer case properly.

[Chadwick717]

Hey guys. Newbie here with an extreme newbie question. I just picked up a 79 c-10. Through this
forum I've been able to do some searches and I figured out that I have a np203 transfer case and a part time kit. (The truck moves in hi without the front hubs locked.)  I am however, having trouble shifting the transfer case, and making sure I am in hi only.  What is the proper process for shifting between lo lock, lo , hi , hi lock?   And how do I make sure I am in hi only?  Thanks so much for the help I have learned so much already here.

[rich weyand]

It's easy to figure out from the shifter, unless your shifter is loose, so I am assuming your shifter is loose.  Also, there is a switch on the shifter box that indicates on the dash, so I am also assuming your dash indicator is non-functional.

First thing.  There is a chrome piece of the shifter that sticks up out of the boot into the cab.  There is an unchromed piece that actually goes into the shifter box on the front of the transfer case.  These are bolted together under the boot.  If they get loose, the shifter will feel wobbly, and move around without shifting the shifter box.

Remove the boot -- four screws, trim ring comes off; four more screws, boot comes off.  Identify the two bolts in the shaft.  Tighten 'em up.  Replace boot and trim ring.  The shifter should now be solid in whatever position you shift the case into, and you can tell what mode it is in by the distance the knob is from the seat.

Second thing.  There is an indicator on the dash.  Probably the left one in the speedometer.  Look up in behind there with an inspection mirror and a flashlight.  Is there a bulb holder there with white and brown-with-white-stripe wires coming from it?  That's the "4WD LOCK" indicator lamp.  Now, when you have the boot off in the above step, notice the white and black wires that come out from under the carpet and go down through the hole.  Those go to a 4WD indicator switch on the very front of the shifter box. Look down through the hole and you should be able to see the 4WD indicator switch.

To debug all this: First, pull the lamp holder in the dash.  It twists one-eighth turn in the "unscrew" direction and pulls out.  Is there a bulb in it?  Is the bulb good?  Get underneath the truck and pull the connector off the switch.  Short the switch connector with a piece of wire.  Does the bulb light?  Is the switch adjusted properly?  To adjust the switch, push it deeper into its mounting hole, then shift the shifter into LOC and back out.  The switch is self-adjusting in the hole, in that it will push out to the correct position.

Finally, the switch may be dead.  NOS GM part will cost you a hundred bucks.  However, there is a reproduction made that works.  It's what I am using.  It is also used by GM as the throttle arm position indicator on a 1969 Camaro cowl induction setup.  Here it is:
http://www.heartbeatcitycamaro.com/store/product/13747/Camaro-Cowl-induction-throttle-switch-1969/

You probably should replace the mounting clip as well.
http://www.heartbeatcitycamaro.com/store/product/13748/Camaro-Cowl-induction-throttle-clip-1969/

[Chadwick717]

Great info! Thank you so much. I'm gonna start looking to the indicator lamp when I get home.  I guess my question is also a little more basic than that. I have an automatic so should the truck be in park or neutral when shifting the transfer case?  When I'm in hi the transfer case shifter knob should be straight up correct? And hi loc angled back towards the seat?  Mainly I'm concerned about driving on the roads in hi loc accidentally.

[Dan75k20]

There is a great write up on chuckschevypages.com on how to properly adjust an np203. I swaped my 203 for a 205 my 203 shifter levers were all messed up the shifter kept shifting into neutral good luck with the 203 its not real easy to adjust when in the truck

[Chadwick717]

I guess what I'm asking is how to tell if I am in hi or hi loc with the part time kit.  When I think I'm in hi, the front shaft still spins when I watch the truck drive away, but I can get down and spin it with my hands.

[rich weyand]

You can shift from HI to HI LOC and back any time when the hubs are in LOCK, such as in the winter if you lock the hubs before you leave home, as I do.  I normally lock them on first snow and keep them locked more or less all winter, for sure any time there is a chance of bad conditions.  I put them in FREE once the weather turns.

When the hubs are in FREE, you can shoot from HI LOC to HI any time, but the vehicle must be stopped or moving very slow (1-2 mph) to shift from HI to HI LOC.  This is because the front hardware is either not spinning at all or only spinning slowly due to drag in the hubs and transfer case.  So you can't slide the splined collar onto the splined part of the shaft when they aren't close to the same speed.

When the hubs are FREE and the transfer case is HI, there is no oiling of the rear output shaft bearing of the NP203.  It was designed to be full-time, so there is no oil pump per se.  The chain for the front drive flings oil against the inside of the case, which runs down into oil ways and back to an oil reservoir for the rear output shaft bearing.  You can drive that reservoir dry, and then burn up the rear output shaft bearing of the transfer case.  MY solution is to put the transfer case into HI LOC for the first couple miles of my first drive of the day, to fill that reservoir, then shift out of HI LOC to HI, which I can do while moving.  There is no need to do this when the hubs are locked, because the hubs are driving the differential, driveshaft and the chain in the transfer case, oiling the rear output shaft bearing reservoir.

[rich weyand]

I guess what I'm asking is how to tell if I am in hi or hi loc with the part time kit.  When I think I'm in hi, the front shaft still spins when I watch the truck drive away, but I can get down and spin it with my hands.

Fix the indicator lamp.

[Chadwick717]

Rich thanks for all the help.  I'll get on that indicator lamp.

[FlatBlack77]

this is all very useful information!

I just got a '79 a few weeks ago and was doing some reading trying to find out more about it and it turns out mine has the part time kit 203 aswell (low loc-low-n-hi-hi loc shifter) and it has lockout hubs.

i was not aware that i could drive around with the hubs locked and switch from high to high lock at any time while moving

[rich weyand]

this is all very useful information!

I just got a '79 a few weeks ago and was doing some reading trying to find out more about it and it turns out mine has the part time kit 203 aswell (low loc-low-n-hi-hi loc shifter) and it has lockout hubs.

i was not aware that i could drive around with the hubs locked and switch from high to high lock at any time while moving

Yeah, just as long as you are not spinning the rears.  When you go from HI to HI LOC, both axles have to be going the same speed.  I kick it in and out of LOC on the fly a lot in the winter when the roads are clear but the parking lots and side streets still aren't.

[FlatBlack77]

awesome good to know!

[Chadwick717]

Quick update. I did get under the truck yesterday while changing the oil and I saw that the connector to the switch was disconnected, so I reconnected it.

Still no light on the dash, and I ran out of time, so I need to check the bulb, but I ran out of time.

I did find the pins holding both rods to the shift knob were gone, both rods were still in the holes on the levers, but I replaced the pins. Still can't tell from feel if I am going In between hi or hi loc.  I can shift into neutral and down into lo and lo loc, then back into neutral, and back into one of the hi-s.  Basically it feels like there is only one option on the hi side of neutral.  Should the be a noticeable clunk or something going from hi to hi-loc?  I guess I need to get under there and adjust the linkages per chucks chevy pages. 

[rich weyand]

No clunk if stopped.  If you are going 1-2 miles per hour, there should be a clunk when it engages.

[75gmck25]

If you have a stock NP203 I don't think they ever included a dash indicator lamp. 

Also, if someone has added locking hubs you also have non-factory setup that won't work the same as original.  Locking hubs were never an option with the NP203 because it was full-time 4WD.  There is a differential in the transfer case that allows it to stay in AWD all the time.  The shifter changes from high to low range, and locks the transfer case into true 4WD.

A stock NP 203 has a shift pattern of:
LowLock (2:1 gear reduction, Tcase differential locked to 4WD),
Low (AWD, 2:1 gear reduction),
Neutral,
High, (AWD)
HighLock (Tcase differential locked to 4WD)

After a part time conversion kit installation (e.g., Milemarker 501 kit) the shift pattern becomes:

4x4 Low
2x4 low
Neutral
2x4 High (Normal Street use)
4x4 High

Bruce

[rich weyand]

If you have a stock NP203 I don't think they ever included a dash indicator lamp. 

Beg to differ.  My 78 K10 had one as built, which was extra wiring outside the normal harness, the switch on the shifter, a lamp socket on a pigtail, and the plastic lens with 4WD LOCK lettering on the LHS lamp behind the speedometer.  The switch on the NP203 shifter mounts in a bracket that is part of the shifter and has no other purpose.  The 1978 parts book calls out the switch.

On mine, the lamp was burned out, and the switch was broken.  I replaced both and now have the indicator lamp functional with no changes required.