NP231 Internal Gear

ScottR

ScottR

It's never done.
Joined
Mar 21, 2005
Location
Raleigh, NC
Long story but I need to swap the internal gear in my NP231 t-case. Is this just pressed in? Any tips on how to get it out?
1410118774601.jpg


Apparently in 1994 the gear cut in the NP231 changed. I was given a 1988 tcase 21 spline. My broken 1997 case is 23 spline. I thought it wouldn't be a problem to swap the input gear. Well, the pattern is slightly different so I need to swap the gear in the picture above. (Or get a 1995+ np231.)
Thanks

@Jody Treadway
 
Last edited:
I would just take the half case and slap it flat on the concrete. I've heard they sometimes fall out when washing them. :D
 
Not sure what the difference is. I had a 21 spline to replace for a crawl box, we just took the 23 out of the broke box and put it right into where the 21 spline was. all we changed was the input, did nothing with the sun gear
 
livetorun- I will give that a try. :)

upnover- I bet the input gear and the housing that you were dealing with were both pre 94 or both post 94. I am dealing with a pre 94 housing and post 94 input gear.

It's documented here-
http://www.novak-adapt.com/knowledge/np_nvg_input_gears.htm

"Because of differences in the cut of the gear, as a general rule, one should not interchange 1987-1993 gears with 1994-present gears. These years are not always hard and fast delineations. If one is not absolutely certain, disassembly and inspection is required."

Wish I had known that before I swapped the parts and installed it in the jeep...
 
Seems like there is a snap ring that holds it into the case half. Either way, a little smack onto a tab;e top should loosen it. If not, you can always punch it out via a drilled hole on the donor case.
A little heat won't hurt progress either. Never underestimate the power of a yard sale toaster oven in the shop.
 
Lee- you are the man! Slamming the t-case half on the concrete floor worked the ring right out.
Ken- thanks for the suggestion to contact Lee. :smokin:

20140908_214144.jpg


Now, for the fun part of removing the t-case to swap the rings...
 
Well, it took 55 days to get my jeep back on the road since busting the t-case housing at the Hatfield McCoy trails. A huge thank you goes out to Lee Crawford at TLC Transmission. He worked with me to figure out what I needed. I was given an older style NP231 housing with a 21 spline input. I needed a 23 spline to match my transmission. I needed (now I know) an older style input shaft that has the correct gear tooth cut on the planetary's. (They changed the way they are cut in ~95.)
Lee took lots of measurements and went through his parts catalog to find the input gear that had the correct spline, length, gear cut, bearing, etc. Once, I installed that- the whining went away. The drive to work this morning was cool, but felt great to get Betsy back on the road.

@transman731
 
Back
Top