It's a modulator valve .....it connects to manifold vacuum

 

You will need to use the bracket that came from the 305 carbuerator for accell.cable and t.v. cable. VERY IMPORTANT that the T.V. (Throttle Valve) cable is hooked up and adjusted properly-as that is what regulates pressures in 200/700R4 models, and controls shift points an kickdown duties. Also, you will need some means of wiring up the electrical circuit for tourqe convertor lockup if you wish to retain that feature-which you most certainly will want to,or else you wouldn't be choosing to use a 700R4. It must include being wired thru brake pedal activation to disengage upon brake application. If you do a search thru trans. forum and/or knowledge base you can surely find what you need. Enjoy your re-engineering! :sweat: PS: Some later model TH350's utilized a lock-up convertor, but not sure which ones, or if lockup characteristics would be compatible 350/700. However; many rodders on this site are running 700R4 with lockup WITHOUT having it controlled thru computer. I have 86 Caprice and mine is wired independent of computer with manual activation switch on dash. (Had my trans.builder wire it up for me after be did trans.buildup) I know I've seen a schematic for it before (on this site), but I can't recall exactly when/where. Most anyone on this site whom really knows this trans.well could probably give you more insight.

 

please see attached picture.

I have an 86 gmc truck (305) that i am replacing with a rebuilt 305 from an 85 caprice classic. My truck had a 350th, but i would like to replace it with the 700r4 that came out of the caprice.

now what is this little diaphragm on the rear passenger side of the th350, i did not remove from the car so i did not see where it was connected to.

also, will the same brackets on the carb for the th350 work properly for the 700r4?

also, I will be reusing the existing truck computer with the accessories. does the computer have a lead for the converter lockup?

thats not a 700r4, they dont have a modulator.

 

thats not a 700r4, they dont have a modulator.

I know, what does it do...and why does my 700r4 not have it.

 

As far as answer to why 200/700R4's don't have vacuum modulator valve- the Throttle Valve cable that I referred to earlier gives reference to valvebody in those transmissions, thus controlling pressures/shiftpoints (along w/governor and servos). The TH350/375/400 models use vacuum modulator instead of throttle valve cable to give reference of engine load-influencing shift point(s). Just a different means of referencing throttle position/engine load. However;with the TV cable on the 200/700R4's it is EXTREMELY important that this cable is adjusted properly-due to the fact that it has direct effect on controlling pressures by it's action(s) on the valvebody. If improperly adjusted too far out of parameters-you can cause severe damage to the trans. The TV cable has adjustment where the cable housing passes thru the throttle cable bracket. If car had factory cruise that cable also passes thru same bracket. As previously mentioned-you should go thru the knowledge base and I'm certain you should find all the info.you need to complete the swap. Hope this has helped you a bit so far.

 

As far as answer to why 200/700R4's don't have vacuum modulator valve- the Throttle Valve cable that I referred to earlier gives reference to valvebody in those transmissions, thus controlling pressures/shiftpoints (along w/governor and servos). The TH350/375/400 models use vacuum modulator instead of throttle valve cable to give reference of engine load-influencing shift point(s). Just a different means of referencing throttle position/engine load. However;with the TV cable on the 200/700R4's it is EXTREMELY important that this cable is adjusted properly-due to the fact that it has direct effect on controlling pressures by it's action(s) on the valvebody. If improperly adjusted too far out of parameters-you can cause severe damage to the trans. The TV cable has adjustment where the cable housing passes thru the throttle cable bracket. If car had factory cruise that cable also passes thru same bracket. As previously mentioned-you should go thru the knowledge base and I'm certain you should find all the info.you need to complete the swap. Hope this has helped you a bit so far.

thanks for the help. It seems the throttle bracket from the truck 305 is the same as the one that came out of the caprice, so that should not be a problem. I hope the wiring to the 350 carried a lock up circuit for the converter (extra just not in use). will plug it in and see. thanks for the info

 

most all trucks with th350 were th350C lockup converter

from 81-86

ifit has an electricla plug on the side then its a C

the plug should be the same style but if not they are mor eof a strectched oval shape like on the th350c from an 81 c-10 pickup that i have and you would juct need to swap the connector is all

real simple

good lcuk