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NP203 Troubles, Weighing options

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JeremiahAB03

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I bought 1978 C10 a couple months ago, and I have always wanted a 4x4 but have not been able to afford one. I figured I'm young and stupid, so I will attempt a 4x4 conversion on this truck.

I picked out a 1975 K10 Heavy half frame, no real rust or rot for about 250 bucks. It has a TH350 and an NP203 t-case. I should have thought to check before dropping the engine and cab in place, but like I stated before, I'm young and stupid and figured all would be well.

I got the engine running, which took a while due to some wiring gremlins, and general shenanigans. Went to put the trans in gear and I got this terrible whirring/grinding noise. Didn't matter what gear the t-case was in, and didn't matter what gear the trans was in, besides neutral and park of course. So I fired it back up and left it in gear, so it was making the grinding noise, and I laid down underneath the truck and was listening around the trans and t-case, and was able to discern that it was 100% coming from the t-case.

Started pulling the 203 apart, starting with the driver side "inspection cover". Everything in there looked clean and operable at the least, so I moved to remove the lower drain cover on the passenger side. There lay my problem, the drive chain wasn't even attached to either of the large gears. It seems that it broke clean in half, not sure when or how or why. So I dropped the rear driveshaft, removed the tailshaft and found that the spider-gear housing had been broken as well, likely when the chain first gave way.

So my options are to rebuild the one I have, which seems like it just needs a new chain and spider gear set. Or I can buy a used NP203 off of marketplace or ebay. Lastly, I've heard a lot about swapping to the 205 case, but it seems that the 205 swap is a bit more costly to do. What is the best course of action here?
 
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The 203 isn’t the most desirable case, mostly because every loves new shiny aluminum and a better ratio

That typically means one can be had for little to nothing
 
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As you can see 203's are plentiful and cheap! I really like the way they operate as designed. Full time handles great. Fuel savings usually aren't that great with the conversion anyway.

A part time kit really makes it a turd IMO. The case doesn't oil properly when in "2wd" mode, you have to engage 4wd periodically to oil the front output. In fact, that may be why your chain broke...
 
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nitro_rat said:
As you can see 203's are plentiful and cheap! I really like the way they operate as designed. Full time handles great. Fuel savings usually aren't that great with the conversion anyway.

A part time kit really makes it a turd IMO. The case doesn't oil properly when in "2wd" mode, you have to engage 4wd periodically to oil the front output. In fact, that may be why your chain broke...e
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Fuel savings are not great agree. But ive never seen a Square lifted 4 in that didnt have massive front shaft vibration while in full time at 60 mph. Just depends on end use and set up.
 
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Recon 78 said:
Fuel savings are not great agree. But ive never seen a Square lifted 4 in that didnt have massive front shaft vibration while in full time at 60 mph. Just depends on end use and set up.
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In all fairness, if I cared about gas mileage, I probably wouldn't have bought a V8 pickup truck. I'm mainly just going to be driving the thing to work and for errands, maybe going out to buy big parts every now and then. Probably some occasional 4-wheeling but nothing extreme
 
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JeremiahAB03 said:
In all fairness, if I cared about gas mileage, I probably wouldn't have bought a V8 pickup truck. I'm mainly just going to be driving the thing to work and for errands, maybe going out to buy big parts every now and then. Probably some occasional 4-wheeling but nothing extreme
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Fair enough
I was agreeing that gas milege was not great and that there are other reasons for a part time kit. Good luck in your build
 
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JeremiahAB03 said:
Appreciate the offer, but if I went part time, I think I'd have to switch to a lockout front axle as opposed to the non lockout that is currently in it.
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You would only need lockouts, not a whole axle.
And to change a 203 back to stock all one needs to do is put their non part time tailhousing on in place of the part time equiped one
 
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I ran warn hubs in a D44 front with a stock 203 transfer case for years. Helped gas mileage and drivability a lot. Drove that truck across the country a couple times. Looks like you have a few options here to get another 203. I took 2 of them apart to get the range boxes and put the extra parts in a crate. If you end up trying to rebuild your 203, I have chains, gears etc. from the 2 cases I pulled apart.
 
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If you're trying to run 4"+ lift a part time kit is the cheapest way to get rid of the front driveshaft vibration. It's more of a band-aid than a fix.

If one really wanted to run a 203 at that lift the real fix would be to drop $$$ on a balanced CV driveshaft from a reputable shop, shim the front differential pinion angle as necessary, and cut and turn the inner C's to correct the caster angle. RCV CV front axle shafts ($$$) would be a nice bonus. All that is $$$ and above average fab work.

Just don't forget to lock in your hubs and engage 4x4 at least once every 500 miles or so to make sure everything in the transfer case is properly lubed.
 
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nitro_rat said:
If you're trying to run 4"+ lift a part time kit is the cheapest way to get rid of the front driveshaft vibration. It's more of a band-aid than a fix.

If one really wanted to run a 203 at that lift the real fix would be to drop $$$ on a balanced CV driveshaft from a reputable shop, shim the front differential pinion angle as necessary, and cut and turn the inner C's to correct the caster angle. RCV CV front axle shafts ($$$) would be a nice bonus. All that is $$$ and above average fab work.

Just don't forget to lock in your hubs and engage 4x4 at least once every 500 miles or so to make sure everything in the transfer case is properly lubed.
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I ran a 203 with a 4" lift for over a decade in a pickup. Dana 44, no shims or custom work. Stock front GM CV shaft that was the right length, don't remember what combo the shaft was out of. No part time kit just Warn hubs. Never had a vibration. Drove it coast to coast twice back in the late 90's when gas was around a buck. Vibration is not a guarantee, you just have to run it and see. Also ran that axle on stock shafts with 36" swamper radials, never broke anything.
 
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Same here,, 4in lift 36in tsl's no probs for 20yrs. Didn't even know about lubing by putting in 4x4. When i found that out, i looked at my case. It had drip leaks at all places you could possibly have them.
Oil was getting to every it needed no prob.

But thats my rig, i understand they all dont act the same
 
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