Can I swat the F&R diffs from a 76 K25 to 81 K20

[Mark R]

I have a 1976 K25 parts truck and wish to swat the F&R differentials into my 1981 K20 truck. My question is this doable or do I need to also change drivelines? The trucks have different transfer cases too.
Thanks for any help you can provide in this project

 

[Bextreme04]

they should be almost identical.... the 76 will have a D44 front while the 81 has a 10 bolt. Rears would most likely be the same but not necessarily. As far as drivelines go, you might need adapter u-joints. What are the specific diffs and drivetrain setups for each?

 

[DoubleDingo]

You can try, but you'll definitely hurt your hands doing so. SWAT. Oh you meant swap? Yeah had to be swap. Check the perch widths, and wheel mounting surface to wheel mounting surface widths, and if everything matches up you should be golden.

 

[BKING33]

axles are interchangeable. only issue may be u-joints that should be it. sold many sets over the years for swaps.

 

[75gmck25]

A '76 K25 is probably an NP203 transfer case, unless its a manual transmission with NP205. It should be a 14 bolt rear axle, and if the GVW is high enough it will be a full floating axle. Most common ratio in the K25 of that year is 4.10.

Driveshaft and U-joint configurations are a little different from year to year, so it may or may not bolt right up. It will help a lot if you have a complete donor truck with complete driveshafts. If needed, a good shop can probabably modify them to get the right u-joint connections to the transfer case.

Bruce

 

[AuroraGirl]

A '76 K25 is probably an NP203 transfer case, unless its a manual transmission with NP205. It should be a 14 bolt rear axle, and if the GVW is high enough it will be a full floating axle. Most common ratio in the K25 of that year is 4.10.

Driveshaft and U-joint configurations are a little different from year to year, so it may or may not bolt right up. It will help a lot if you have a complete donor truck with complete driveshafts. If needed, a good shop can probabably modify them to get the right u-joint connections to the transfer case.

Bruce

fun fact, in 1980 the only transfer case optionable in K series was np205. i read this in the shop manual and some online literature.
i should clarify, 3/4 ton. 1/2 ton could have a np203

not related to anything, just wanted to share