NP205 rebuild, 23 to 29 spline conversion

[thrashingcows]

OK I did this conversion to my Automatic 23 spline NP205 during the 2wd to 4wd conversion on my crewcab. I wanted the 29 spline since it is running a NV4500.

I will not go into the specifics of actually rebuilding the whole NP205, since there is a couple good threads that cover this already. Here are a couple site links to the threads I used to help me rebuild my NP205.

http://67-72chevytrucks.com/vboard/show ... p?t=469726

http://www.fourwheeler.com/how-to/trans ... sfer-case/

OK you first need to pull the transfer case and get it on the bench, I will assume if your reading this that you know what your doing, and can remove a NP205 from your vehicle without anyone holding your hand.

First is getting the adapter off. I had to use a universal and a long extension to reach the bolts.



You can see the threads have a sealant on them.

[thrashingcows]

Here is what the 23 spline input shaft looks like.



And the adapter.



Outer Snap ring off the input bearing.



And this shows where the snap ring sits in the adapter. We need to remember what each level in the adapter does for the proper machining.

[thrashingcows]

Again I won't go into the tear down of the transfer case. But here it is all apart and ready for cleaning.



All cleaned up.





My machinist appreciates it when I bring him nice clean parts to work on. Yours will too I'm sure.

[thrashingcows]

Just some more reference pics of the 23 spline bearing and adapter. I take a lot of these just so I can go back and refresh my memory if I am unsure of something.







And since the seal area will have to be opened up for the larger 29 spline input shaft seal, there will be lots of room for the retaining snap ring. This shows the 23 spline retaining snap ring.

[thrashingcows]

Here is the input shaft bearings, 23 on left, 29 on right.







When you buy the 29 spline input shaft bearing make sure you purchase one with the snap ring already present and installed. I did not do this and there was a lot of down time and hassle to finally find a used one...and then I had to pay dearly for it.

[thrashingcows]

The 23 spline adapter uses two seals on the input shaft. They are the same but each faces opposite to keep gear oil and ATF separated.





Not sure if the OEM 29 spline adapter runs two seals or not, but once the machining is done for the larger seal there will not be enough material for a double seal regardless.

[thrashingcows]

I had the old stuff, and the new bearing and snap ring, and input shaft seal when I dropped everything off to be machined. Showed him how it all went together originally, then what I needed it to look like with the new parts. Only took him a few hours to machine everything.

Case all machined for larger bearing....



Adapter all finished...or so I thought.

[thrashingcows]

Bearing in it's new home....





Adapter and the new seal placed for comparison.

[thrashingcows]

And new bearing and snap ring placed in adapter to make sure everything fit.

[thrashingcows]

I purchased the new input shaft off E-bay. Very nice piece, and fit perfectly.

Here is a comparison, Auto (23) on left, and manual (29) on right.





But again you don't get everything you need. I needed the retaining snap ring since the rebuild kit does not come with one, nor does the 23 spline unit fit the 29 spline shaft. Thankfully Quad4x4 had what I needed. I also grabbed a couple of the rubber yoke seals at the same time.

[thrashingcows]

So finished up the rebuild and was ready to install the adapter.





Go to install the adapter and...Ooops something to fit right.



Seems that I/we (my machinist) didn't take every measurement into account. The bearing and snap ring required a little more room to clear the adapter. I took a bunch of measurements and then brought the adapter back for some more machining.

[thrashingcows]

Adapter all machined properly now.



Now that the adapter fits properly I could install the seal. Use red lock tight to help secure the seal in place. Once the machining is done there is "just" enough material to hold the seal, so the red lock tight helps secure it just a little bit better.





Be very careful not to get any red loctite on the seal surface...it could ruin your seal.

[thrashingcows]

The rebuild kit I got did not have two gaskets for between the case and adapter, only for the smaller 23 spline unit. So I had to cut it open with an exacto knife.




Perfect fit...



All back together and ready to be installed.

[thrashingcows]

You will also need a new 29 spline coupler. Again I sourced mine form E-bay. But yet AGAIN it did not come with everything I needed.

As delivered...



I noticed when comparing it to my 23 spline coupler that it was missing the center snap ring. This stops the coupler from drifting back and forth on the shafts and wearing out the front faces of the seals. So I went to my local bearing supply house and was able to find a snap ring that fit perfectly.



Installing the snap ring was a bit tricky. Finally had to get it set nice and square in the bore, then use a large socket to carefully tap it down into place. took a few tries to get it set right.



And hear is a visual for how heavy these beasts are....

[thrashingcows]

Well that is about it, hope it's clear enough and I didn't miss any information.

Good luck!