Check it out guys! I busted open the transfer case this weekend and found out a cool thing or two:
1) Speedo gear:
Driven gear from spicer 23 is interchangeable into SM420 transmission
Drive gear has the same pitch & outer diameter, but the inside where it presses onto the shaft is smaller.
I found a sm420 speedo gear set on ebay... so I could make an adapter sleeve to put it in the transfer case... but maybe I'll just put it in my transmission instead. Ebay gearset ratio is 20:7 driven:drive, and my original gear is 19:7. Same outside diameter on all gears. Seems wierd, I'd expect the 19 toother to be smaller than the 20 in order to mesh properly with the same drive gear? Maybe that's why it's worn out?
driven gears:
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https://i.imgur.com/87NIHUz.jpg?1[/img]
drive gears:
[img]
https://i.imgur.com/aRDd8fI.jpg?1[/img]
2) Easier way to shift transfer case
Background: The only way I can ever get the t-case in neutral or 4 low is by beating on the shift rods with a sledgehammer... the single stick shift lever does not have enough leverage to go into any gear but 2wd or 4hi.
Given the difficulty, I was expecting the shift shafts to look all rusty inside, and hoping that a good cleaning would fix my problem. Not so, they are shiny and nice!
So I was considering to convert to twin stick... but for now I decided to put lighter springs behind ball detents of shift rods.
It was super easy to swap out the springs, could easily be done with case under truck. The springs are behind a screws on the outside of case adjacent to the aft shift rod casting bumps.
Here are pictures:
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https://i.imgur.com/GMljCT0.jpg?1[/img]
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https://i.imgur.com/QQGsqvj.jpg?1[/img]
I left the one closest to the NAPCO tag alone, since I can already shift into 4hi just fine
Since I'm replacing all the shaft seals i had to take off all the drive flanges... holy hell they were tight! Took all my strength behind a breaker bar with a 3' cheater. Broke two 1/2" drive extensions in the process. Clamping the flange in a vice on a heavy table is a must.
[img]
https://i.imgur.com/ocIFw0q.jpg?1[/img]
Very satisfying though  :-))
As far as i know, the spicer 23 is the same as a dana 23 and is a mirror image of the dana 24. Same rebuild kit works for all mentioned.
