TH350>700R4 Swap

[1slo_camaro]

I have my TH350 to a 700R4. i was told there is a kit that has the wiring and everything for lock up and all that. Its in a 78 C10 2wd LB with a 350. sorry im new to this forum but been all around Jeepforum, Cherokeeforum, LS1tech and all from past and i will get an intro up soon and some details lol

Just looking for some info on this swap so i can get O/D and get a little better gas MPG

[85gmcguy]

Painless Wiring sells a lock-up kit that works well.
http://www.summitracing.com/parts/prf-60109

[TravisMartin]

I did the same swap, also in a '78 LWB C10. It's very easy, just have to move the crossmember back 1 1/2 inch. The driveshaft is so nearly the same you don't have to worry with it. The PRNDL won't have the 1st gear position, but you can retrofit parts from a later truck if you think you need it; I never did.

Welcome to the forum; post some pictures of your truck!

[1slo_camaro]

thanks, i plan on getting a Lokar 23in floor shifter and pull the handle off the column when i do this swap.

Here is a snap shot of her, the PO did a lot of half ass work and im just trying to tinker and get her looking better, but paint will be the last thing. and i got these wheels for 60 bucks..... cant beat that over the rallies haha first thing will be tint, 700r4, and drop her down a little

[1slo_camaro]

Also i have been told that you can just wire an On/Off switch to control O/D..... is this possible? if so, where do i run the wires from? or am i set on having to purchase that kit?

[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.

[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?

[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.

[1slo_camaro]

lmao thanks

im not to worried about the speedo honestly. more the functionability of the trans right now. i have a gps speedo and my phone has an app for that hahah


but i dont have any wires coming off my plug. the trans was in my camaro and i pulled it when i sold it so it can go in my truck

[1slo_camaro]

does anyone have the part number for the brake switch? im sorry i know its a lazy move but the internet on the boat is ridiculously slow so searching for things really sucks

[superwade57]

You'll also want to get a TV cable vs a detent or " kick down" cable its crucial to the operation of a 700r4 dont do it and it'll burn ur tranny up. Make sure its adjusted correctly its really easy to do. This is all important because that cable on a th-xxx tranny only controls passing gear kick down. On an xxx-R4 Tranny its actually controls a valve that opens variably with throttle pedal position hence the name "t v cable " "throttle valve cable"
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[1slo_camaro]

Originally Posted by superwade57

You'll also want to get a TV cable vs a detent or " kick down" cable its crucial to the operation of a 700r4 dont do it and it'll burn ur tranny up. Make sure its adjusted correctly its really easy to do. This is all important because that cable on a th-xxx tranny only controls passing gear kick down. On an xxx-R4 Tranny its actually controls a valve that opens variably with throttle pedal position hence the name "t v cable " "throttle valve cable"
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i agree with this to a point..... simply because i have ran several 700s for thousands of miles without a TV cable and never had one issue. but yes i plan on taking care of that.... which opens another question i never thought abuot...


how do yall connect your tv cable? im not with my truck right now so i dont remember if the q-jet has a spot for it on the throttle arm, can i just grab a bracket off a TBI truck? anybody?

[superwade57]

I've had friends run without them fine....I had mis-adjusted cable take a tranny out once... for lack of any other problem found... Not positive but It may affect power distribution and economy too. It would make sense if it did.
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[1slo_camaro]

welp no 700R4 for me.... while underway with the coast guard cutter Vigorous, i come home to find i was robbed and someone stole my 700R4, pressure washer, stihl chainsaw, and 4.5 lift springs for a jeep grand cherokee this really sucks!

[Billy81]

Sorry to hear that some low life stole your stuff man that really sucks.

[tlawre87]

welp no 700R4 for me.... while underway with the coast guard cutter Vigorous, i come home to find i was robbed and someone stole my 700R4, pressure washer, stihl chainsaw, and 4.5 lift springs for a jeep grand cherokee this really sucks!

That sucks man. Sorry to hear it. But grab a police report and start hitting the pawn shops and craiglist. You may be able to find some of it.

[clinebarger]

Stock 700R4's have a "TV exhaust check-ball" That acts as a fail-safe if the TV cable breaks or becomes unhooked....Creates High Fixed Line Pressure, Keeps the trans from burning up right away. But running high pressure is bad too.

[1slo_camaro]

well they pulled the converter out of the trans and cut the hose off the pressure washer. i doubt they were pawning it lol. ive been looking around local scrap yards and recycle yards fingers crossed. but doubtful ill find it