How to I work a 76 K5 TH350/NP203??

[TIMSPEED]

I heard it's "Full Time" 4wd, so..what gear do I put it in or what?

[1969 GMC]

The transmission? Drive, of course

Sorry, I had to...seriously though, if you are gonna drive it on the roads, I'd put it in Hi. This way it will let the center diff work.

[TIMSPEED]

Originally Posted by 1969 GMC

seriously though, if you are gonna drive it on the roads, I'd put it in Hi. This way it will let the center diff work.

So, you're saying put the transfer case in 4-Hi, and then just drive it? (For Normal Driving) What about for offroading? Is there a tech article explaining the way the Np203 works?

[1969 GMC]

the NP203 is always in 4wd mode, but there are 5 positions on the shifter:
Hi, Hi-Lock, Neutral, Lo, and Lo-Lock.

i dont know of any articles about the 203 offhand, but you could try Googling or also search Pirate4x4 or ColoradoK5.

in a nutshell, the 203 acts as a center differential in addition to being a transfer case. Imagine that the Blazer is just a big axle, and the frontend of the blazer is one wheel, and the rearend is the other wheel. The 203 is the diff. Basically, when in Hi or Lo, the front and rear axles can spin at different rates of speed (much like wheels on an open diff axle can spin at different speeds). You would use either of these positions when driving on pavement, to make up for inconsistencies in the road and cornering...and nothing will bind up.

When driving in Hi-Lock or Low-Lock, now imagine that big axle with a locker in the diff. This makes it so that the front and rear axles spin at the same speed all the time, like how the wheels on the big axle spin at the same speed all the time. This is the 203 equipped truck's equivalent to a part-time 4x4's 4-Hi or 4-Lo. In a part time truck, the axles always spin the same speed, as there is no center diff like in the 203.

Hopefully this doesn't confuse you more...if it does, then try searching, as I dont want to type any more, lol.

[TIMSPEED]

1969GMC,
You made it perfectly clear. Thanks for putting in easy to understand terms Now, what if the front hubs are Manual Locking? What does that throw in the equation?

[Jonboy]

If the front hubs are manual locking, make sure they are locked in when you are in Hi-Loc or Low-loc. The original hubs were not locking, they were always locked in. The theory behind the manual hubs it that it will save a bit of fuel if they are unlocked when not needed. If there are manual locking hubs on the truck, there is a decent chance that someone might have installed a part time kit in the transfer case. If that is true, then the "Loc" positions would be 4WD, and the hi and low positions are 2WD. I believe you need to lock in the transfer case every few hundred miles to lube the case if it has been converted.