Thread: 400 trannny question

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here is a question to the tranny guys out there.
as the 400 tranny has a electric kick down can a switch be mounted to the shifter to either override the throttle switch or be used instead of the kickdown. i was thinking about this today and also was thinking of the ramifications of hitting the switch once one throttles up a big block while in high gear instead of it shifting down at approx 3/4 throttle application.
would this work or would there be ramifications such as leaving the tanny on the road.
just a thought ??????

Never seen a TH400 with an electric kickdown. TH400's use a vacuum operated kickdown as opposed to a detent cable.

well i know there is a vacum servo that is involved but isnt the kickdown controlled by throttle position, i know the kickdown can be messed with by the switch which is either by the carb or under the dash on the footpedal

the th400 has a electric kick down sol. mounted on the valve body, thats controlled by a switch at the carb, or under the dash. you can operate it by hand, but its only gonna mess up you trans.

My '73 caprice has no electrical hook ups on it anywhere SBC 400, TH400. Absolutely no electrical hooks on the carb. The kickdown is operated solely by vacuum pressure. GM may have, perhaps in later models made some provisions for some electrical downshifts and I know that there is much electrical in newer model OD trans, but I have been thru a couple of early TH400's and not seen this. I could be wrong, but I'm pretty sure.

well i kind of thought that if you could mess with the kickdown switch at any time while driving you could cause some havoc especially kicking it in under full load.
the trany i have is out of a 72 olds 88 it has the vacum servo on the rt side front and on the left side near the middle is a little electrical tab. the other two bop 400 trannys i have are the same.
i think the idea of the vacum servo has something to do with the tranny shifiting up into drive from passing gear . i know my dads 74 pickup had the same type of switch cause he disconnected it when he found i was abusing the 454 in it . made the truck kind of doggy without it. figured it out pretty quick though.
urto are you shure there is nothing on the lt side of your tranny with a little wire hanging out of it. , i may be wriong

Originally posted by urotu
My '73 caprice has no electrical hook ups on it anywhere SBC 400, TH400. Absolutely no electrical hooks on the carb. The kickdown is operated solely by vacuum pressure. GM may have, perhaps in later models made some provisions for some electrical downshifts and I know that there is much electrical in newer model OD trans, but I have been thru a couple of early TH400's and not seen this. I could be wrong, but I'm pretty sure.

urotu, all th400 had a electrical switch for the passing gear. th350 has a cable.

Fair enough, lt1s10. I'll have to take your word for it. I guess that this is my leson for the day. I try to learn something new everyday and this will be todays learning experience.

Thank you

the vacumn modulator is for up shifts only The down shift solinoid is for downshifts there is no such thing as passing gear all that happens is the trans downshifts.You are more likely to blow your motor than the trans by using a hand switch you could over rev the motor .

thanks cook for the responce
i thought it kind of worked that way 12 switch shifts into 2nd and vacume modulator causes it shift back into 3rd.
just needed someone else to tell me it.

Ever sense the automatic trans. has been made there has been a mechanism incorporated into them that allowed the driver to down shift the trans from out of a higher gear into a lower gear with the use of a cable or switch so the driver wouldn't have to take his hands off off the steering wheel every time he needed to do this. most trans. use a cable, but a few use a switch. its called a detent cable or detent solenoid. about the only reason you would need to downshift into a lower gear while driving down the road would be to pass another car on a 2 lane rd (thats all we had in my day). so over the yrs. this cable/sol. came to be called a detent cable/sol.,a kick-down cable/sol., and most of the time in my part of the world it was called a Passing gear cable/sol. some body says there is no such a thing as a passing gear, but I believe there is, and a passing gear cable/ sol. makes it work. thats my story and i'm sticking to it. .

yeah i agree we always called it passing gear cause thats when its needed most.

Can I just leave the kickdown unhooked? I don't really need it on my car. Ted

you know i never thought about that , my build is a 500 caddy in a t bucket , the shift down syst wouldnt need to be hooked up as i think i would have enough jam to move the car along pretty well anyways and i could alway manually shift the tranny into 2nd to pass if needed.

you can leave it loose, you wont have a passing gear. everything else will stay the same. in hi gear WOT you may slip your hi gear clutches. i would hook it up.