How to tell if my NP203 has been converted to part time?

Silver Square · Jun 22, 2024

Got a '77 K15. It's got the NP203, at least it should. I've got the low lock, low, neutral, high, and high lock on the shifter, but the truck has locking hubs. I've been driving the truck in high with the hubs unlocked, is that a good indicator that it's been converted?

I have the truck up on jack stands now, and was playing around. Hubs locked, all 4 tires spin in high, but when I shift into any other range, only the back tires spin, and there is grinding when I try to shift to a different range. I have to shut the truck off and shift to park, then put the case back into high or it'll grind badly when I try to move the lever. Shouldn't I be able to shift it while the truck is in gear? It doesn't seem to like that at all.

Octane · Jun 22, 2024

Silver Square said:
Got a '77 K15. It's got the NP203, at least it should. I've got the low lock, low, neutral, high, and high lock on the shifter, but the truck has locking hubs. I've been driving the truck in high with the hubs unlocked, is that a good indicator that it's been converted?

I have the truck up on jack stands now, and was playing around. Hubs locked, all 4 tires spin in high, but when I shift into any other range, only the back tires spin, and there is grinding when I try to shift to a different range. I have to shut the truck off and shift to park, then put the case back into high or it'll grind badly when I try to move the lever. Shouldn't I be able to shift it while the truck is in gear? It doesn't seem to like that at all.

Need to match road speed with tranny speed.I believe under 25mph,with transmission shifter in neutral,move transfer shifter from neutral to high.While idling engine up slightly,At the right speeds the transfer case wont grind.Takes practice.My np203 hasnt been messed with either.And your wheels should be on the groubd for it to work properly

bucket · Jun 22, 2024

Silver Square said:
Got a '77 K15. It's got the NP203, at least it should. I've got the low lock, low, neutral, high, and high lock on the shifter, but the truck has locking hubs. I've been driving the truck in high with the hubs unlocked, is that a good indicator that it's been converted?

I have the truck up on jack stands now, and was playing around. Hubs locked, all 4 tires spin in high, but when I shift into any other range, only the back tires spin, and there is grinding when I try to shift to a different range. I have to shut the truck off and shift to park, then put the case back into high or it'll grind badly when I try to move the lever. Shouldn't I be able to shift it while the truck is in gear? It doesn't seem to like that at all.

If you can drive in regular HI with the hubs unlocked, yes it's been converted.

Turbo4whl · Jun 22, 2024

Silver Square said:
Got a '77 K15. It's got the NP203, at least it should. I've got the low lock, low, neutral, high, and high lock on the shifter, but the truck has locking hubs. I've been driving the truck in high with the hubs unlocked, is that a good indicator that it's been converted?

I have the truck up on jack stands now, and was playing around. Hubs locked, all 4 tires spin in high, but when I shift into any other range, only the back tires spin, and there is grinding when I try to shift to a different range. I have to shut the truck off and shift to park, then put the case back into high or it'll grind badly when I try to move the lever. Shouldn't I be able to shift it while the truck is in gear? It doesn't seem to like that at all.

No, if the auto trans is in gear and you shift out of high gear, the counter shaft still spins. Nothing to push back when the transfer case is in neutral. So if you are stopped, put the truck in park then you can shift to another gear in the transfer case.

As @Octane stated, you can shift while moving by adjusting engine speed. Keep in mind there are no synchros. Since your 203 has been converted, best to shift it stopped, in park.

Octane · Jun 23, 2024

The extra wear and the insignificant fuel gain is why I would never convert my truck.I get 11-12 mpg as it is.It's a truck,not concerned with any gain.My truck is a real original surviver also.

75gmck25 · Jun 23, 2024

Most NP203’s were converted by one owner, who never passed on the directions to the next owner.

The docs with the kit tell you a converted NP203 has to be run in the 4LOC position about once a month to ensure full lubrication of the chain, output seals, and other internal parts. The chain moving is what circulates/splashes oil throughout the case on a converted 203, and it only circulates oil when it’s in 4LOC.

idahovette · Jun 23, 2024

Also, they shipped an elbow with the kit, to install in the fill hole so you could get a little more fluid in the case.

AuroraGirl · Jun 23, 2024

if someone has hub locks (aftermarket, not spicer) and they have nothing visually distinct from another np203, id just leave them locked and use it as intended. now if you have spicer hubs , i find it less likely someone sourced a manual transmissions trucks axle for the fun of it or at least the parts from it, and i would be personally invested in determining if it was or not.

Silver Square · Jun 23, 2024

It's got superwinch hubs on it. I guess it's been converted since it moves in high with the hubs unlocked. Something is broken though, because I have no front axle drive in either lock position or low. Hopefully the shop can fix it. I just wanted to know if it had been monkeyed with before I took it in so I could tell them whether or not it had been botched by the previous owner.

Old Guy Bill · Jun 23, 2024

From what I’ve read if the Mile Marker part time conversion kit has been installed the shift pattern is changed.
It will be as shown here.

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Silver Square · Jun 23, 2024

Well, I found a stock 203 case not too far away for $100. Figure my best bet is to just get the stock one and have it rebuilt so I know it will operate as it should and sell this problem to somebody more willing to deal with modified stuff.

Is the 1977 K10/K15 NP203 the 2 or 2.5" chain? I see both options, but none of the retailers tell me which one I need for this application.

I'm guessing if I just lock the hubs and leave them that way, the truck will operate properly with a stock 203 case? Or would I need to remove the locking hubs all together?

Can I use limited slip diffs in the front and rear with a stock 203? Think I remember reading somehwre that they don't play nice together, but now I'm finding conflicting info.

Thanks.

AuroraGirl · Jun 23, 2024

Silver Square said:
Well, I found a stock 203 case not too far away for $100. Figure my best bet is to just get the stock one and have it rebuilt so I know it will operate as it should and sell this problem to somebody more willing to deal with modified stuff.

Is the 1977 K10/K15 NP203 the 2 or 2.5" chain? I see both options, but none of the retailers tell me which one I need for this application.

I'm guessing if I just lock the hubs and leave them that way, the truck will operate properly with a stock 203 case? Or would I need to remove the locking hubs all together?

Can I use limited slip diffs in the front and rear with a stock 203? Think I remember reading somehwre that they don't play nice together, but now I'm finding conflicting info.

Thanks.

the hubs should work, but i suspect the stub ends of the original axles are technially stronger than the hubs as they have less parts and dont have mechanisms for sliding etc, but if your hubs are in good shape i cant see why it wouldnt work.

Do you still have the differential or cv unit to the front that balances front to rear to allow you to get turns. if the person "deleted" that , im not sure if you can, it would maybe explain grinding and not wanting to work right

Silver Square · Jun 23, 2024

I don't see a CV, looks like a normal driveshaft with a u joint. Here's what it looks like.

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AuroraGirl · Jun 23, 2024

you need to see the front of the t case to see it, so a pic from in front of the cross member, also you appear to have two different mounts holding the t case on the crossmember
also you need air in tire

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I dont have any pictures of the side you show or of my cv/differential thing

Silver Square · Jun 23, 2024

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Here's some better pix of the front and closeups of the side right where the driveshaft comes out the front of the case. Yeah, I know the tire is low in that pic. I took it when I was looking at the truck before I bought it. I pumped it up before I drove it home. Not sure what's going on with the mount, it looks factory.

How to tell if my NP203 has been converted to part time?

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