I've recently swapped my trucks axles from 1/2 ton to 3/4 ton, and swapped the full time 203 that was in the 1/2 ton, to the 3/4 ton's oart-time (because the dana44 doesn't have locking hubs like the 10 bolt did... and I want 2wd), and now I need to refill the case. My question is, how do I fill it (it's already back in the truck, and I can't find a fill plug), and what do I use? I did a search on how to fill it and found a post suggesting the use of 10w 30/40... And the guys at NAPA suggested ATF; what do I run?

Thanks for the help guys, I appreciate it agian.

need more info what t/c did you install or what year were the axles out of.

Truck is a 1983 Chevrolet k-10. Running gear was 350/350/203 10/12 bolts.
Axles/case came out of a 1975 Chevy K-20, running gear was 350/350/203 d44/14b ff. When I dropped the cases, they both "bled" red... ATF, correct? I told the NAPA guys that the oil was red, and they said it was ATF, and to just run that stuff again.

The NP203 can use dex3 or 10W30 motor oil. if you use gear oil 80W90 or heaver the chain will streach.

Alright, so using the ATF with Dexron is ok... Any ideas on how to fill the case? Cutting the floor of my truck is no problem if need be... I just don't know where the filler is at.

The filler plug is on the back of the case between the rear cover for the front output & the rear output. That is all the fill to plug. :D

Awesome, you rawk! Got the case filled today... Tried to put the rear d-shaft up, and it's about 1.5-2" too short, and the front is the same way. I don't get it, considering the two trucks I used were exactly the same, regular cab long beds.. waa!! :mad3: oh well

Thanks for the help guys, just let this thread die. :)

the pinoin gears are in differnt spots. ie farther away than the other set.

did you try both rear shafts and both front shafts in your truck. did you lay them side by side to see if one is longer/shorter than the other?

i never had a problem running 80/90, but i didnt know about the atf, cool

I layed the front shaft next to the old front shaft... Exact same size. And I measured from the front of the 3rd member (where the diff cover starts) to the yoke on the d44 and the 10 bolt, and they're the same length. I don't get it!! The 14b is about an inch shorter than the 12 bolt... But that doesn't explain the 1.5-2" I gained. I'm gonna measure my wheelbase when I get home today and see if when they lifted the truck, it gained some inches. It shouldn't have, should it? My wb on the 75 was 128.5... I'll update later.

Is the t/c you took out all alum. or is it a heavy cast iron. If you can post pics of both t/c it would help. your vehical being a 83 should have a np208 where the 75 could have a np205 or np 203.

. But that doesn't explain the 1.5-2" I gained. I'm gonna measure my wheelbase when I get home today and see if when they lifted the truck, it gained some inches. It shouldn't have, should it? My wb on the 75 was 128.5... I'll update later.


dude!! you said nothing about lifting your truck!!! thats where it came from!!!


your wheel base is still the same, but now WITH THE LIFT the distance between the tcase and axles has increased. :shaking:

Sorry I didn't mention earlier that it was lifted. :p And both cases are 203's, I had a good friend and GM tech verify that.

I feel really stupid for this, but when I measured my WB, it came out to 133.5... The 75 must've been a short bed (never knew, when we bought it, it had a "custom" wooden flatbed), and my 83 is a regular bed. I'm gonna change driveshafts tomorrow.. Try the 1/2 tons and see if it fits. It should be closer.

Sorry for my newbieness... But that's what this part of the forums are for, right? :grinpimp:

NP 203 uses motor oil, so if it had ATF, it had the wrong lube in it.