75 GMC Full time Vs. Conventional transfer cases

[Jimmy Canuck]

I have a 75 GMC half-ton 4x4 with conventional hubs but it has a 350 in it. Is this stock? I read some old advertisements and it seemed to indicate that only conventional 4x4 hubs came with 6 cyl. engines or was this only on Chevy trucks? I can't check the vin on the cab as the prev owner threw out the original vin tag when switching cabs.....

2nd. What is the difference between a conventional 203/205? transfer case and a full time one?

3rd. My cousin told me to watch out for trucks of these years 73-77? because sometimes former owners have changed the hubs from Full time to Conventional and it does something to trash the transfer case. Maybe lack of lubricant or forgetting to lube the case??????

All this is because when the truck is running either the transfer case or a throw out bearing in the clutch is making a hell of a racket.

[Destructo]

well, a NP203 transfer case is a full-time case AND a part-time case, when the gear selector is not in loc mode its a full-time case, in loc mode its part-time.

What some people do is put hubs in the front because they don't have hubs at all in the front from the factory, but if you put hubs in the front and run them unlocked and the t-case is not in loc range it won't move at all, because the case is differentiated, so you either have to install a part-time kit in the transfer case or leave it in loc range all the time.

NP205 is a part-time case in both 4hi and 4lo, and is gear driven instead of chain driven. NP205 is the toughest transfer case out of the NP203, 205 and 208.

[76bonanza]

I run a 203 with lock outs I dont know if it has a part time kit or not. But I have to lock the hubs and put in loc to get 4 wheel drive in 2 wheel drive the selector is in H and hubs unlocked. I just run it with it in Hi-loc after ever fill up for a few miles to oil up the chain and stuff.

[RockHQ]

Originally Posted by Destructo

well, a NP203 transfer case is a full-time case AND a part-time case, when the gear selector is not in loc mode its a full-time case, in loc mode its part-time.

No, no, no.

The NP203 is a full time case period. It has no part time abilities in stock form whatsoever. A part time transfer case provides torque to the front driveshaft only when engaged by the driver. The 205, 208, 231, 241 etc are part time transfer cases.

The 203 is a full time case with a selectable differential locker. Unlocked, it provides equal torque to the driveshafts as long as their rpm stays the same (no wheelspin). Locked, torque distribution is even to both of the driveshafts no matter what the driving conditions are.

[79C10]

ya just like 76bonanza said my 79 has manual hubs came from the factory as full time 4wd some put on the hubs and changed some gear in the transfer case (this is what one of the previous owners had scribled into the owners manual) but I have to be in hi or lo loc with the hubs locked in to use for wheel drive I use regular hi and lo as 2wd.

P.S. it's not going to hurt anything runing the truck in lo (essentialy 2 lo) sometimes like this summer when I was haulin my grandfathers trailor loaded with shingles back for him I had to use lo to get started but then shifted the T-case in hi ands proceded (the 250 was a little tired) this is alright, right?

[magnethead]

slipping a tcase from lo to hi is perfectly fine. It kinda works like a multi speed bike- it scoots the chain over as it rotates.

Rock HQ got the tcase info dead on. Also, see my page at http://www.auto-chat.net/help . It has some info on T-cases.