Th350 to 700r4x4 conversion

[_Mac_]

What’s up fellas. I have a 75 K5 that I’m replacing the 350/203 tc with a 700r/208 setup. I have the “tall” 4x4 adapter, crossmember from a 83 suburban as well. Anyone have any experience with this conversion?

 

[1973c10]

Welcome

 

[bucket]

Howdy!

You will need a lockup kit to engage the TC lockup at highway speeds, or just wire it to a dash switch. Imho, every single 700r4 in a 4x4 or any truck that does any amount of towing will NEED a trans temp gauge. You will also need to get driveshafts made if you can't find the proper shafts from an 80's truck. Your 203 has a fixed yoke on the rear, the 208 is a slip yoke. Your older 203 probably has a standard yoke on the front output too, where the 208 has a flange yoke. You will also need the correct shifter and linkage. I'm not sure how well the factory 80's setup will jive with the '75 tunnel, but I'm sure it can be made to work. Iirc, JB Fab makes a real nice cable shifter that you could easily mount to the driver's side of the tunnel.

 

[bucket]

Also, I moved this thread to the Trans/T-case section.

 

[Kurnacopia]

A few things will need to happen. First you will need the right adaptors. Get a hold of ADVANCED ADAPTORS: https://www.advanceadapters.com

Talk to them about correct splines and bell housings. Next you will have to move your support bracket. The 700r4 is longer than a TH350. You can do this your self by just moving the support and drilling where necessary in the frame. You will need to take measurements before and after to determine correct drive shaft lengths. Lastly, that 208 transfer case is aluminum. If you are gona 4 wheel in that guy be sure and add some protection from rocks and such. Some plating around the general area is a good idea. Best of luck!!! MK