TH350>700R4 Swap

[gramps77]

Originally Posted by 77c10

I put a 700 in my 77 C10. The way I wired it was to get a brake light switch from a c10 with cruise control, they have two extra terminals on them. I wired on side to the fuse box to a terminal that was hot when the key was on. The other terminal I ran to the trans. Basically what happens is it powers the lock up and then when you step on the brake pedal it disconnects it.

You can go a step further and wire a toggle switch in between the fuse box and brake light switch if you want to control it manually.

Originally Posted by 1slo_camaro

Hey guys so im gonna hopefully throw my 700 in my truck when i get back home..... can i get a few more questions answered? will i have to drill new holes for the c-member? and will the tailshaft be further back so will i need to have my d-shaft cut? and what do yall do about the speedo? just say to hell with it? or what?

for right now i need to do the bare minimum to get it in there and drive without burning up the trans so im probably going to just wire up a switch that i will have to probably switch on and off whenever i slow down unless i can make something work with my brake switch and a splitter to run down to the trans.

so the questions im looking for haha:

Where do i run the Hot wire from the brake to on the trans? which plug/wire? (as far as i know i have 4 prongs on the trans

Do i need to cut my shaft?

Do i need to re-drill my frame for the cross member?


Im not saying you dont know what you are talking about TravisMartin, but i like to hear from more then one person on some things just to see how things are done differently ya know?

77C10 is right, get the other brake switch that is for a truck with cruise. Exactly what I do every time. (7 times now between my 3 Novas, my 77 now, and friends cars)
There should only be one RED wire coming out of that plug on your tranny with four pins. That red wire will then got to one of the extra 2 spades off the brake switch, then the other side of that switch will go to an ignition hot lead at the CB box. I usually put in a 10 amp fuse inline.
If you are trying to JUST get it back and forth or whatever, you can slide the trans Xmember back and use just the aft holes. Ive been meaning to go back and drill the new rear holes on the crossmember but have been lazy and not done so.
You wont need to shorten the driveshaft since the long tailshaft is what these trucks come with if equipped with a TH-350 originally (9" vs 6", which is the difference youd probably need to shorten it if different)
As long as you have the mechanical speedo output, you can hook it right up. It may not be accurate, so you'll have to find one of those speedo calculators to make sure you have the right gears. In fact, you may want to do that before you install it if you want to use your speedo. Its much easier to work the tailshaft drive gear NOT in the truck if you need to change it. If you do have the mechanical speedo output, pull the speedo output housing and see what color gears are in there. The color will dictate how many teeth each is. Before this gets entirely more long winded, I figured Id stop here.