Different T-cases

[77DuallyCowboy]

Ok, I have a question for you 4x4 guys that know your
t-cases. I have a 78 3/4 4x4 with the "full time" T-case, how does it work?? ive been told its kinda like an open differential in how it works, however i proved that wrong today. I can very easily kick out the rear end in snow in 4wheel, NOT 4 lock. I thought that if the rear spins it engages the front, and vise versa. Or is this only at low speeds?? also, what t-cases came in 73-87 trucks and 73-91 crewcab trucks? (I have a 88 crew cab dually 4x4 thats why im wondering.) Thanks guys.  

[77DuallyCowboy]

I forgot to mention, what lube goes in these T-cases??? ive heard motor oil, gear oil, and ATF.  

[roundedline]

Full-time is dictated by the rear section. The case has an internal differential that splits power to the front and rear axles when the shifter is not in one of the locked positions. In Hi-Loc or Lo-Loc, the differential locks to power to both driveshafts. Removing the driveshaft and trying to drive in the nonlocked position, would send all the power to the yoke with the missing shaft. It’s like an open rear axle differential where all the power goes to the tire with the least traction. Putting the case in a locked position, would split power  equally to the front and rear, so you’d be able to drive the truck with one driveshaft.

Oil for it is 10w-40 or straight 30w.

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[1976Scottsdale]

My case is an original 1979 np203 that had Dexron 3 in it when I bought it... this was not a good thing, it was leaking out of every seal and gasket.  Now it has 80w90 in it, it runs very well with this, but now that I know what it needs, I will dump it and add 30w to it.

[WVBrady]

I remember when these first came out.  Some magazine had a write-up on them, extolling their virtues.  Then some guy wrote in that if you jacked up one of their wheels, that they would not pull themselves off the jack.  They went out and tried it, and he was right!  

Brady

[1976Scottsdale]

I had mine layed over on two wheels and she still pulled herself back over when i locked in the hi loc.  i do not have manual hubs, so I just move the shifter and I am there.  Good God I love posi front and rear axles.