700r4 to th400 swap

[87highsierra2500]

First off hello to everyone out there I will be looking forward to talking to some of you. I have an 87 gmc high Sierra v2500 and my 2nd 700r4 is going out. I have a strong tin 350, 4in lift with 35in tires and 4.10 gears and I got my hands on a th400 with a 208 t-case, same t-case I have now.I'm just wondering if there's anything I need to do or be aware of before I install it at work. Like is the cross member going to have to be moved or can it stay and what about drive shaft lengths. The 700r4 isn't the original trans it originally had a Muncie 4spd according to the vin and rpo sheet. Thanks, Josh

[Greenlee]

I did this exact swap. The drive shafts were the same length. The cross members were different. You need to use the cross member that came with the th400, and it will need to be moved a couple inches and drill new holes in the frame. The cooler lines were the same. The transfer cases have different spline counts so you need to use the one that came with the th400. You will need a switch for the kickdown for the th400. You also need to run a vacuum line.

That's all I can think of. Me and a buddy did the swap in an afternoon and I drove the truck home that evening. It was pretty straight forward.

[87highsierra2500]

So what's different about the crossmember I didn't know there was that much of a difference

[Greenlee]

Originally Posted by 87highsierra2500

So what's different about the crossmember I didn't know there was that much of a difference

I could be wrong, but seems like it was a completely different shape where it supports the transmission/transfer case. I didn't pay too much attention to this because the th400 crossmember came with the new transmission and it was just as easy for me to use it.

[87highsierra2500]

I guess I will have to check on that and see if it is