Why are there lock hubs on a 75 if it is a full time 4x4?

[markrazz]

was wondering if someone could explain the whole 4x4 set up on a 1975 blazer.
My belief is that these are all full time 4x4 if auto
If this is the case why do the hubs turn and have lock outs ?
I just got the truck so haven’t gone through the 4x4 actions yet and want to understand what’s going on..
Also what are the positions for the shifter and options it offers?
Thanks

 

[HankScorpio]

If you have a np203 transfer case then it was originally "full time" 4wd. There was a kit to change the t-case to part time 4wd that was fairly popular. In this case the drive flanges would have been swapped to locking hubs. Also sometimes locking hubs were added without the part time kit. In both cases this was done to help with fuel economy.

 

[markrazz]

If you have a np203 transfer case then it was originally "full time" 4wd. There was a kit to change the t-case to part time 4wd that was fairly popular. In this case the drive flanges would have been swapped to locking hubs. Also sometimes locking hubs were added without the part time kit. In both cases this was done to help with fuel economy.

So how do I figure out what I have going on with my setup
The guy I got it from has no idea so can’t ask him

 

[HankScorpio]

Unlock the hubs, drive the truck in various shifter positions with someone watching your driveshaft. If you have a part time kit there should be a 2wd position where you have rear drive without the driveshaft spinning. This could be difficult to determine though, sometimes the shaft will spin due to drag on the bearings and hubs, sticky grease moving things. In a perfect world in 2wd unlocked the front shaft will not move. The np203 is half steel half aluminum. A np205 is all steel.

 

[onetonbb74]

Early 203s were all steel. I had one in my 74, aluminup tail housings came out in 1975. I had hubs to keep it out of 4x4, (although the front shaft would spin) on the street.

Np203:

Hubs locked: (dash to seat)
Low lock
Low
Neutral
High
High lock

Hubs unlocked: (dash to seat)

Low lock
Neutral
High lock

Hope that helps. With the hubs unlocked you put the shifter in high lock and go.

The np203 takes motor oil as well, do not put gear oil in a 203.

 

[onetonbb74]

If it has a part time kit, the low and high positions become 2wd positions...that will keep the front shaft from spinning.

 

[markrazz]

When I took it out first time I had to put the shift all the way forward to get moving..
Did find out that I needed transmission fluid and now moves proper but still all the way forward .
I will try other positions tommorow tomtrynfig more out

 

[imiceman44]

When I took it out first time I had to put the shift all the way forward to get moving..
Did find out that I needed transmission fluid and now moves proper but still all the way forward .
I will try other positions tommorow tomtrynfig more out

This means someone put locking hubs but didn't put a part time kit.
All the way forward is locked so the front being unlocked the tcase is locked and will spin front and rear driveshafts equally.
All the way back it will also work for low range.
If you lock the hubs you'll be able to drive in the position before last for normal all wheel drive.
That will also confirm what I said.