Transmissions which one? 71 K10 standard to auto

[jbassC10]

1971
After market 307
4x4
4spd manual

I want to put in an automatic transmission?
Which one do I need to retrieve to do so! Year? Model?

Thanks for your time!
-Tyler

[57taskforce]

The easiest route is to use the oe parts to put a turbo 350/205 into it along with the shift linkage/column shift which are available from a 70-72 automatic 4x4 truck.

[jbassC10]

So basically grab a turbo 350 and find the linkage I’d prefer which would be a typical floor shifter/T handle or I don’t know drag style instead of replacing column.
Hmm interesting

So I wonder what year do I need to find a turbo 350 from? Roughly same or near year I assume

[57taskforce]

It requires not only the 4x4 th350 but you’ll need the th350 to 205 adaptor, 27 spline shaft coupler, and to change the transfer case input shaft from the 10 spline coarse to the 27 spline fine, to do it right any way. There is a bit of a short cut to the different input shafts that isn’t as strong. Torque king and others sell a 10 spline to 27 spline conversion coupler. You can get the case adaptor from torque king, ORD and others as well. The transfer case mounts in the same place with either transmission so the driveshafts stay the same length in case you are wondering. Any 4x4 th350 should work as far as I am aware

[mrein3]

Originally Posted by 57taskforce

It requires not only the 4x4 th350 but you’ll need the th350 to 205 adaptor, 27 spline shaft coupler, and to change the transfer case input shaft from the 10 spline coarse to the 27 spline fine, to do it right any way. There is a bit of a short cut to the different input shafts that isn’t as strong. Torque king and others sell a 10 spline to 27 spline conversion coupler. You can get the case adaptor from torque king, ORD and others as well. The transfer case mounts in the same place with either transmission so the driveshafts stay the same length in case you are wondering. Any 4x4 th350 should work as far as I am aware

As 57taskforce points out, GM used two different input shafts in the NP-205. All the manual transmissions came with a 10-spline shaft, the TH-350 version used a 27-spline input shaft.

The easiest way to go is to find a doner and take all three pieces, the turbo 350, the adaptor, and the t-case. Make sure the coupler comes with it. The coupler slides over the turbo 350 output and the NP-205 input and rides around in the adaptor.

Speaking of the adaptor, when it is sitting on the ground before you install it is a good time to replace the oil seals. The adaptor front seal keeps the transmission fluid in the transmission and the back seal keeps the t-case oil in the t-case.

The good news is if your truck is currently a stock 4-speed/NP-205, to swap to a turbo 350 and NP-205 is a plug and play deal. GM made up for the differences in transmission length by using different length adaptors. In other words going from a stock manual anything to a TH-350 you use the same crossmember and the same driveshafts.

[jbassC10]

Holy smoke! Thanks guys! Pretty big deal! lol wish me luck in time!
First step is to install the power steering kit I purchased first! 🤘🏼Then I’ll move onto the tranny directions!! Geez! I’m excited to learn so thank you guys 100%!!