Full-time AWD on 78 K-10 with TH350?

**rich weyand** · 09-30-2010, 09:34 AM

As I mentioned in another post, I found a place that has a lot of original dealer brochures, including the one for the 78 Chevy pickups.

In the brochure's SPECIFICATIONS section, under FOUR-WHEEL DRIVE [MODELS], there is a row labeled TRANSFER CASE that is split into MANUAL TRANS and AUTOMATIC TRANS.

For MANUAL TRANS, the TRANSFER CASE is CONVENTIONAL, while for AUTOMATIC TRANS, the TRANSFER CASE is FULL TIME.

Elsewhere in the brochure, under SPECIAL MODELS, in the Four-wheel drive section, it says "All 4-wheel-drive models with available automatic transmission come with full-time 4-wheel drive with all controls conveniently located inside the cab."

Anyone know what the difference is? The RPO codes on my truck say it had the TH350 from the factory, and the column looks original, but it also has the normal (I think) LOC-HI-NEUT-LO-LOC transfer case lever on the transmission hump, and that also looks original.

Or was it just that with the auto trans, you also got the auto-locking hubs, so "all controls conveniently located inside the cab" just meant you didn't have to get out to lock hubs?

Rich

**GreaseDog** · 09-30-2010, 12:45 PM

with the NP203 full time case, you would get automatic locking hubs... which translates to they're automatically locked 100% of the time.

seriously, 203 equipped trucks came with drive slugs, which did not have the ability to be disengaged. automatic hubs didn't come out until the NP208 came out in 81.

**rich weyand** · 09-30-2010, 01:29 PM

Thanks, GreaseDog, you set me on the right path for some manual reading and net research.

Looking at some transfer case ID photos on the net, it is definitely an NP203. HOWEVER, I also have switchable LOCK/FREE hubs on the front.

SO, if it was an open differential in there (unmodified NP203) I shouldn't be able to go anywhere if the transfer case was unlocked and the hubs were unlocked, right?

THEREFORE, the NP203 must have been modified at some point to lock the differential to the rear, with the LOC positions used to engage the front axle.

I think.

Anyway, it is definitely an NP203. I definitely move when in either unlocked position on the transfer case lever. The front drive shaft is definitely disengaged when in either unlocked position on the transfer case lever. And the front drive shaft is definitely engaged when in either locked position on the transfer case lever, because if I also lock the hubs, she will buck on dry pavement when turning.

So, modified NP203? And the LOC-HI-NEUT-LO-LOC on the transfer case lever should be understood to be 4HI-2HI-NEUT-2LO-4LO instead, right?

Rich

**ryan_thompson87** · 09-30-2010, 02:59 PM

Originally Posted by rich weyand

Thanks, GreaseDog, you set me on the right path for some manual reading and net research.

Looking at some transfer case ID photos on the net, it is definitely an NP203. HOWEVER, I also have switchable LOCK/FREE hubs on the front.

SO, if it was an open differential in there (unmodified NP203) I shouldn't be able to go anywhere if the transfer case was unlocked and the hubs were unlocked, right?

THEREFORE, the NP203 must have been modified at some point to lock the differential to the rear, with the LOC positions used to engage the front axle.

I think.

Anyway, it is definitely an NP203. I definitely move when in either unlocked position on the transfer case lever. The front drive shaft is definitely disengaged when in either unlocked position on the transfer case lever. And the front drive shaft is definitely engaged when in either locked position on the transfer case lever, because if I also lock the hubs, she will buck on dry pavement when turning.

So, modified NP203? And the LOC-HI-NEUT-LO-LOC on the transfer case lever should be understood to be 4HI-2HI-NEUT-2LO-4LO instead, right?

Rich

Your correct, someone put a part-time kit in it.

**rich weyand** · 09-30-2010, 09:39 PM

OK, now this may sound stoopid to you guys, but....

Anybody know where I can get the parts needed to convert it BACK to full-time?

See, with a part-time kit, you basically have 2WD if either the TC or the hubs are unlocked, and 4WD with locked axles if they are both locked.

With the stock NP203 and selectable hubs, you have 4WD w/open diff, 4WD with locked axles, or 2WD by unlocking the hubs and locking the TC. I actually like that better.

So, where do I get the parts to UNDO the part-time kit? Probably what I need are the spider gears if it is the Mile Marker kit.

Rich

**Crummy** · 10-01-2010, 10:20 AM

I had a '76 with that option.

**GreaseDog** · 10-01-2010, 10:22 AM

you had a 76 with standard equipment.

**rich weyand** · 10-01-2010, 05:02 PM

Looking around, I see that drivetrain.com has rebuilt, unconverted NP203s for sale. About $1250, including shipping to here and return shipping on the core.

Ouch.

Any better alternatives?

Rich

**~Super~Midget~** · 10-01-2010, 05:59 PM

why not just leave the hubs locked in and drive in the 2hi position, then you don't have to get out to lock them in??

**rich weyand** · 10-01-2010, 06:14 PM

Well, sure. People tell me, Oh, you have to get out in the bad weather to lock the hubs to get into 4WD, and I'm like, No, you look out the window before you get in the truck and lock the hubs in the nice warm garage if it looks like you might 4WD today. I get that.

But I really like the idea of differential 4WD in the snow, and I don't have that now. I have 2WD and 4WD w/locked axles. Well, with the stock NP203 you can have all three.

Rich

**Your41Plague12** · 10-10-2010, 10:04 PM

Keep in mind if you have a stock NP203 with manual hubs, the front end parts will be coming apart on you if your truck is lifted a decent amount. The driveshaft will still spin whether the hubs are locked or not. My dad had a '78 K10 with a 4" lift on it and he wanted to kick himself in the *** for lifting it. He never put the part time kit in, and that would have saved it.