Author Topic: Swap F&R diff between 76 K25 and 81 K20 truck  (Read 852 times)

Offline Mark

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  • driver is a 1981 K20, spares 1976 K25 & C25
Swap F&R diff between 76 K25 and 81 K20 truck
« on: September 10, 2020, 06:06:39 PM »
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

Offline JohnnyPopper

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Re: Swap F&R diff between 76 K25 and 81 K20 truck
« Reply #1 on: September 11, 2020, 02:37:07 PM »
It will probably work, but what are you gaining?

Different ratio, lower miles?

If the 76 has a NP203 transfer case you'll want to install a part time Kit and locking hubs, or expect already bad mileage to be worse.

Are the wheel bases the same?

Inquiring minds want to know...
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction