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Purchased a th400


ChrisM

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So after doing Alot of thinking, i found a th400 that I'll have to have rebuilt.

 

What I need to know is what I need to do to swap from my th350 to the th400.

 

Parts, cross member, everything I'll need for the swap!

 

Thanks everyone

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Hey Chris,

 

I'm sure a lot of members have done this and you will get lots of input. This is what I remember:

 

- crossmember is the same, just moved to a different set of holes in the frame. th400 is further back on the frame.

- trans mount is the same.

- downshift mechanism is different - th350 uses a detent cable from carb to the trans. th400 uses a switch behind the gas pedal. You will need to make up some wires to supply power to pedal switch and then to downshift switch on th400.

- dipsticks are different.

- driveshaft is different, I believe the th400 is shorter.

- driveshaft yoke is different.

- shifter lockout mechanism is the same.

 

If I think of anything else I will let you know.

 

Good luck!!

Mike

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Gas pedals are the same and I believe the bracket that holds the kickdown bracket is already there. All you do is have to get a new switch, wire it up and away you go. Lol. Good luck!

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My car did not have the kickdown switch bracket. Here it is:

 

https://www.opgi.com/chevelle/7CCH119/

 

And:

 

https://www.ebay.com/itm/Chevelle-Cowl-Induction-Throttle-Switch-Bracket-1970-1972-50-203693-1/183081090292?fits=Model%3AChevelle&hash=item2aa07bbcf4:g:WJoAAOSw7rdaiN~4&vxp=mtr

 

And here's the switch:

 

https://www.opgi.com/chevelle/PZ00415/

 

And:

 

https://www.ebay.com/itm/1970-1972-Chevelle-El-Camino-Cowl-Induction-Throttle-Switch-TH400-Kick-Down/323119447546?fits=Model%3AChevelle&hash=item4b3b6b7dfa:g:riMAAOSwW9RaYgcM&vxp=mtr

 

You run a wire from the "IGN" terminal in the fuse block to the switch and another wire from the switch to the terminal on the left side of the transmission. They make harnesses for this but they're costly. If you have or are installing a console shifter, it's easiest to run the wire from the switch then under the carpet into the console then through the shifter cable hole. The stock way is through the firewall then down to the transmission.

 

Some TH400's have two terminals, one is for the switch-pitch converter, if it has it. Consult your transmission shop.

 

You'll want the accelerator arm to hit the switch when the gas pedal is about half way to the floor. When you get on it, the switched power forces a downshift and holds the lower gear longer.

 

This is what mine looked like. The original plate gets removed and discarded.

post-201-0-23742200-1520601410_thumb.jpg

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Man, Paul thank you so much! I am picking up the trans on Sunday and next week it goes in for a rebuild.

 

I got a whole bunch of other parts in over the last couple of days! Hopefully in the next few weeks it will be a runner and driver! I'll keep everyone updated

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  • 2 months later...

Hey everyone, so I am trying to Install the kickdown switch, I got both the switch and bracket from opgi. Now, the switch only allows 12 volts to flow through when the switch is completely open, meaning the gas pedal has to be all the way to the floor. Does this sound right?

 

Thanks guys

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The kick down switch is moved when accelerating and switch should be set to engage after burner when accelerator is pushed to the floor.  Calibrating or setting the switch is just a matter of moving the spring loaded plunger forward at least half way with your finger, release back to stop and that should set switch.  I don't exactly remember but I believe the switch when mounted requires no adjustment but could be wrong.  Make sure you have power to switch.

 

Doug 

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Hi Doug, thanks for the reply, I did check the switch for power while slowing moving the plunger, and i didn't get power until the switch was moved pretty much to the end of its travel, forgive me for sounding like a newb haha but do you have to take the switch apart in order to change the point at which the switch allows power to flow through?

To me the way it is right now just doesnt make a while lot of sense, id have to put my foot to the floor as of right now to make the car downshift, just doesnt seem right.

 

So I guess what iam asking, is yes is there some sort of adjustment for this switch?

 

Thanks again for the input!

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Hey Chris,  The Kick Down Switch is initiated around the half way point while Pedal must be to floor to activate switch.  Not certain why it is this way but must be a reason.

 

As far as being able to activate switch around half way down would probably startle one and that's why under those traffic conditions you would simply down shift to get the acceleration you need (again in traffic).  Does this make sense?  That's my reasoning anyway.

Basically, if After Burner kicks in with pedal to floor, your done...........................

 

Doug

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I had zero luck using the "adjustment feature" of this so-called self adjusting switch.

 

I bent it's mounting arm so the switch closed and sent power to the transmission when the accelerator pedal was halfway to the floor.

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Doug, ok I get what your saying! I think once I get it on the road for a test drive in a weekend or so, I'll find out if I like it I guess haha.

 

Paul bell, did you take the switch apart to do so?

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Thanks Steve, I had found a driveshop shop around me and with the right information, I had them build me a brand new driveshaft!

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  • 7 months later...

Hey guys, so after driving the car for the summer, obviously I have found some things. Couple of leaks on my transmission (th400) all I can handle myself seeing as how I cant get ahold of my rebuilder. One thing I just want to make sure of before I try, is the tail shaft housing is leaking, other than pulling the driveshaft and the bolts holding it to the back of the trans, will it just slide off? Also does anyone know what seals it? Is it a gasket? Rubber o-ring?

Thanks everyone 

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