700r4swap

[tattoosteve]

i have a 86 k10 suburban and pulled the 700r4,i’ve got a freshly built th400 with trans case and torque converter,what issues or modifications will i have?

 

[Wes Harden]

Welcome @tattoosteve
Many of us were just in your neck of the woods. I drove through Monticello on Thursday.

So the th400 will have a 32 spline output shaft, the t case for the 700r4 will a 27 spline.
The t case adapter will be a 4 bolt pattern, the th400 is 6 bolt.
Th400 case is 25" long the 700r4 is 24", so drive shafts might or might not work.
Also the cross member might need new holes on the frame.

 

[tattoosteve]

ty wes,my 400 has t case and torque converter matching from the donor suburban,all recently freshened up.not even sure about 700 ordeal,may be torque converter may be transmission,i’ll more than likely just put 700 up for sale as is and see what i can get and use that towards new drive shafts if necessary.so if 400 has 32 spline then ill def need different shafts or yokes ?

 

[tarussell]

ty wes,my 400 has t case and torque converter matching from the donor suburban,all recently freshened up.not even sure about 700 ordeal,may be torque converter may be transmission,i’ll more than likely just put 700 up for sale as is and see what i can get and use that towards new drive shafts if necessary.so if 400 has 32 spline then ill def need different shafts or yokes ?

What Wes is saying is that the output on the TH400 transmission is 32-spline and the TH700R4 transmission would have been 27-spline.
This means that whatever transfer case you go with must have the proper input female splines to match.

To avoid confusion it would be wise and helpful for you to post up good pictures of the T-case and adapter that you intend to use with this conversion.
While you’re at it post up pictures of your old adapter and crossmembers so we can be certain of what you had verses what you need going forward.

So many years have gone by that what should have been in your application might not be there at this point - please post quality pictures so we can help direct you without confusion.

Also, you will need to change out the flex plate to match the bolt pattern for the TH400 converter.

 

[tattoosteve]

i understand what he was saying,i literally took my 700r4,tcase and converter out of my 86 k10,went and bought another suburban that only has about 1000 mi on complete rebuild and i pulled the 400 ,transfer case and converter from it ,all still connected ,and put it in my 86.i already had aftermarket universal flex plate on my 350 crate so it’s all bolted in except the driveshafts,had heard i will have issues now with that is why i asked.i will post pics later when back in town and ty for helping

 

[Wes Harden]

So the th400 is out of a 4wd and has a transfer case and adapter? Yeah if so it will go in.
You'll need the correct flex plate, add a vacuum line for trans modulator, manifold vacuum. The kick down switch and wiring at throttle.
Depending on which t case is mated to the th400 will dictate cross member and drive shafts.
If the parts are available from donor, use donnor cross member and front shaft. The rear shaft might work if you have a burb, conversion u joint might be needed, if diff is different. If a k5 then a custom rear shaft will probably be needed.

@tarussel like pictures. Very easy for Premium member to upload and post pictures. Not so much for reg members.

 

[imiceman44]

i understand what he was saying,i literally took my 700r4,tcase and converter out of my 86 k10,went and bought another suburban that only has about 1000 mi on complete rebuild and i pulled the 400 ,transfer case and converter from it ,all still connected ,and put it in my 86.i already had aftermarket universal flex plate on my 350 crate so it’s all bolted in except the driveshafts,had heard i will have issues now with that is why i asked.i will post pics later when back in town and ty for helping

As far as I know, from 85 up the different combos offered used the same length driveshafts, you can confirm if you line them up next to each other.
GM compensated with the length of the adapter to have the same driveshafts