Swap F&R diff between 76 and 81 truck

[Mark65]

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

[kwmech]

Axles are very doable, shaft lengths would depend. The one that may give you an issue would be the front

[57taskforce]

It should be a pretty straightforward swap. I don’t believe you’ll have drive shaft issues but a tape measure would confirm one way or the other.

[Mark65]

Thanks all for the info

[Zoomad75]

Depends on the t-case situation. The axles bolt in. The earlier front shaft should be the Saginaw style where you have individual saddles for the u-joint on the front output yoke. Also the rear shaft on the early one might be fixed yoke if it's a 205.

The front on the later truck will most likely have a flange style mount for the cv to the front output of the t-case. Also, if the later truck has a 208 it most likely is a slip yoke rear output.

But as long as the size of the u-joint is the same at the front and rear diffs as the axles you are pulling out you should be able to re-use the shafts.