3/12/2023 - 3/30/2023
Transfer Case Rebuild and Installation of Transmission and Transfer Case Into Chassis
The rebuilding of the transfer case was a little more challenging than I initially thought that it would be. First off, Parts are very difficult to come by, and when they do come along, they are expensive and if they are used, not much better than what you are starting with anyway. I was lucky to find a transfer case out of a 1967 K10 that, as luck would have it, was only 5 minutes away from me. Moreover, I was able to get it for $100, so I totally scored on that one!! I am very lucky to have run across that deal due to the fact that there was a lot of wear in my transfer case. My initial plan was to use the original case that came in my truck and scavenge the other one for parts, but seeing as how the one out of the K10 was much, much better I altered course and opted to use that one instead. This was of course after I put in all the effort to clean, paint, and prep everything in the original case for rebuild. Oh well….I will just rebuild the original case in time and will have it for a spare. Also, the other case came with an adapter for the transfer case, so it is really good to have another one of those seeing as how they were only produced for the 1967 model year.
As stated, parts are terrible to come by. This includes the oil seals in both the transfer case and the adapter. 1967 was the first year of the "married" transmission to transfer case setup in the K10 and K20 series 4x4 pickups. It was also the last year of the SM420. After 1967, the SM465 came into being. That essentially makes the adapter that mates the SM420 to the Rockwell T-221 transfer case kind of a unicorn of sorts. The coupler that connects the output shaft of the transmission to the input shaft of the transfer case is also unique to the 1967 model year. Anyone who has been down this restoration path probably has found that the seals are difficult to come by if not downright impossible. Well, after digging around the inter-webs and YouTube, I have found the seal and it is still in production! It is super hard to come by no doubt, but I wanted to share it all with you in the event you need to source it as well. This is the same seal that is in use in the T-221 transfer case by the way. While there is an alternative seal solution (SKF 17381 being one), it is not of the original opposed double lip design. It is however likely a superior seal due to the higher temperature rating, but the opposed lip seal, IMHO, is better for the adapter due to the need to keep gear lube opposed in both the transmission and the transfer case. At any rate, if anyone is looking for it, I found the seal at Point Spring and Driveshaft Company (
https://pointspring.com/). The part number is an Axletech (or Meritor) A1805E447.
I ended up using the Meritor/Axletech seal in the adapter, and the SKF seals in the transfer case at the yoke outputs.
Another challenge with the transfer case rebuild for me was the process of shimming the bearings to set end play. This was the main cause for concern with the original transfer case as well. I followed the manual and it says (depending on which one you go by) to put on the rear bearing cap and shims for the input shaft, tighten down the cap and set the end play on the shaft to .015". The problem was that the bearing on the rear, under the bearing cap seemed to move in and out of the bore an awful lot. It would not go all the way into the inside of the case but it would go just below the mating surface which caused the front bearing to move out a good 3/8" or so. At this point, I went ahead and hooked up the transfer case to the transmission and adapter and bolted it up. The adapter didn’t allow the bearing to move in and out, and I tried to move the shaft forward and backward from inside the transfer case, but there was no way for me to measure end play doing it this way. I concluded that the bores for the bearings in the original case were likely worn as there was also indications that at some point, the bearing was changed out (it was not the original bearing) due to a failure. The rear of the input shaft was tore up, and the bearing cap itself was cracked.
For comparison, I took a telescoping bore gauge and did a comparison with the other case that I have and it seemed to be tighter. I didn't put a mic on it, but the bore was definitely a bit smaller on the other case. It was at this point that I opted to just use the other case as the gears, shafts, and components all looked better anyway.
I did have difficulty in setting up the end play on the other bearings, but after some messing around with it, I eventually got it configured.
Another problem that I had was with the threads for the nut that secures the yoke on the rear output shaft. When I disassembled the case, I put the nut on the shaft and used a hammer to tap out the shaft. Well, I didn’t have the nut all the way down (important safety tip for next time!!) and I mushroomed the threads on the shaft slightly as well as on the nut. During the assembly process when I was installing the rear yoke, I foolishly tried to force the nut on using my impact wrench….super bad idea. I tore up the threads in the nut, stripped it out and made the threads on the shaft worse. At this point I stopped for the night (it was 11:30PM) to revel in my stupidity.
After determining that the threads in the nut and on the shaft were 7/8x14, I order a tap and die and got them cleaned up on the shaft (I had another nut from the other transfer case).
From that point on, the assembly went well. I did notice as I was putting the top cover on that the original springs for the balls that lock the shift forks were smaller on the original case. After closer inspection it looks as if they were cut down at some point. I put the longer springs on from the replacement case first and the shifting was extremely tight. I put the smaller springs in and the shifting seems to be much nicer. I concluded that this was a “mod” probably done at some point due to the lever being too tight to pull when shifting into 4WD.
The gasket kit that I ordered for the transmission did not come with any adapter gaskets that go between the adapter and the transfer case, so I had to make my own. I ended up using extra shims that I had as templates and they fit perfectly.
Finally, I was able to lower the transmission and transfer case into the frame and get it bolted up. I also filled both gear boxes with gear oil. Having the body off is nice….all I needed to do is pour the oil in from the top of the transmission where the gear shifter goes and I took the top off of the transfer case and did the same. On the transmission, you just fill until it comes out of the fill hole on the side. Same goes for the transfer case, but I ended up putting the plug in and adding about an extra ˝ quart of gear oil to hopefully allow for additional lubrication of the upper end.