4x4 th400 to 4x4 th350

2g4gsquared

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Ethan
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I'm wonder exactly how hard it would be to swap a th350 in place of a th400? I have a fully built th350 that I have in my first mud truck (76 k10) but my motor had a little to much power for the half ton so I picked up a 83 k20. The k20 has a blown motor and a th400 transmission that is unknown if it is good or not. So I decide to just put my good th350 in it since it is already built with all tci parts in its place. Only thing is I don't know if I can use the th400 transfer case? Also when I ruined my k10s front diff it twisted both of my drive shafts. So can I use the k20 drive shafts for my current set up? Should I use the transfer case I already have paired with the th350? All help would be appreciated with mud drag season coming up... thank you in advance
 

nvrenuf

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The th350 is 27 spline and the th400 is 32 spline plus the bolt pattern on the rear of the trans cases are different.

You'd need the correct adapter and tcase input shaft. Converting a 27 spline tcase to 32 is fairly common and requires machine work because the 32 uses a larger input bearing, I don't know of any conversion bearing to put a smaller (male) 27 spline input into a (female) 32 spline case.

You will also need a drive sleeve for the 27 spline set up.
 

2g4gsquared

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k10 k20 c30
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350 400
If I swap the whole setup transfer case and transmission both can I use the same drive shafts that are in the truck for the th400 tranny or will I have to find new drive shafts
 

nvrenuf

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Each combo will have slightly different length driveshafts from each other (3”-5”).
 

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