sm420 stuff

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Apr 29, 2002
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I know I am bugging everyone with questions today, but was also considering sm420 conversion, was looking at tech section and saw the install, do you not have to change the ouput shaft on the sm420 so it will mate with the4 speed tc, or is that $200 adapter plate kit all I need?
 

woody

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the SM420 output is 10 spline and matches the 73-older t-cases. AFAIK, there is NO adapter from the SM420 to the fine-spline 74-newer t-cases. (AA might have one, but it would be a LONG adapter and not just the plate)

The 73-older t-cases are 16% lower in the low range and still 1:1, so you do get a bit better crawl.

IMO, finding a 73-older t-case will be cheaper than replacing a mainshaft in the SM420 (if one is even available) and likely cheaper than the AA stuff (if that's even available)

(am I even here today....d'oh!!)
 

Mace

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AA does make the adapter but it is like $400
Find a plate and case (sell the 4 speed to finance the new case.. )

Or get a really old case (the brittle ones) for next to nothing because no one wants them, and stuff the gears in to the 4 speed case :)
Much stronger..
Oh yeah, then get a plate adapter ;)
 
Joined
Feb 8, 2002
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190
sm-420 mated to 4-speed transfer case w/plate style adapter. Key 10spline input gear w/4-speed teeth count.

420.jpg

421.jpg

422.jpg
 

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