ChrisM Posted March 8, 2018 Share Posted March 8, 2018 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 Quote Link to comment Share on other sites More sharing options...
Mike Brichta Posted March 8, 2018 Share Posted March 8, 2018 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 1 Quote Link to comment Share on other sites More sharing options...
snomobeelr Posted March 8, 2018 Share Posted March 8, 2018 Cross-member is the same just slides back to other mounting holes in Frame. I do not remember if the Yoke is different. Then getting the Driveshaft shortened. I believe that is it Quote Link to comment Share on other sites More sharing options...
ChrisM Posted March 8, 2018 Author Share Posted March 8, 2018 Thanks guys, this is a good start. Are the gas pedals the same? Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted March 9, 2018 Share Posted March 9, 2018 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! Quote Link to comment Share on other sites More sharing options...
ChrisM Posted March 9, 2018 Author Share Posted March 9, 2018 Ah this is Awesome! Thanks a lot Quote Link to comment Share on other sites More sharing options...
Paul Bell Posted March 9, 2018 Share Posted March 9, 2018 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. Quote Link to comment Share on other sites More sharing options...
ChrisM Posted March 9, 2018 Author Share Posted March 9, 2018 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 1 Quote Link to comment Share on other sites More sharing options...
ChrisM Posted May 26, 2018 Author Share Posted May 26, 2018 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 Quote Link to comment Share on other sites More sharing options...
72-CLASSIC_RIDE Posted May 27, 2018 Share Posted May 27, 2018 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 Quote Link to comment Share on other sites More sharing options...
ChrisM Posted May 28, 2018 Author Share Posted May 28, 2018 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! Quote Link to comment Share on other sites More sharing options...
72-CLASSIC_RIDE Posted May 28, 2018 Share Posted May 28, 2018 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 Quote Link to comment Share on other sites More sharing options...
ChrisM Posted May 29, 2018 Author Share Posted May 29, 2018 . Quote Link to comment Share on other sites More sharing options...
Paul Bell Posted May 29, 2018 Share Posted May 29, 2018 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. Quote Link to comment Share on other sites More sharing options...
ChrisM Posted May 29, 2018 Author Share Posted May 29, 2018 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? Quote Link to comment Share on other sites More sharing options...
Monteman1971 Posted May 29, 2018 Share Posted May 29, 2018 I'm a little late to the party but just an FYI...a Chevelle drive shaft is the same as a Montes as long as they are the same set up..... Chevelle shafts are a bit easier to come by. Steve 1 Quote Link to comment Share on other sites More sharing options...
ChrisM Posted June 3, 2018 Author Share Posted June 3, 2018 Thanks Steve, I had found a driveshop shop around me and with the right information, I had them build me a brand new driveshaft! Quote Link to comment Share on other sites More sharing options...
ChrisM Posted January 22, 2019 Author Share Posted January 22, 2019 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 Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted January 22, 2019 Share Posted January 22, 2019 Hey Chris, the th400 tailshaft housing should be a gasket. Quote Link to comment Share on other sites More sharing options...
ChrisM Posted January 22, 2019 Author Share Posted January 22, 2019 And would you know by chance if it will just slip off once the shaft is removed and the bolts are removed? Thanks Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted January 22, 2019 Share Posted January 22, 2019 Hey Chris, usually a slight tap with your hand by the tailshaft seal (driveshaft seal) should do it. Quote Link to comment Share on other sites More sharing options...
Paul Bell Posted January 22, 2019 Share Posted January 22, 2019 The tail housing gasket is just that-a gasket. While you have the tail housing off the unit, replace the driveshaft seal. It installs just like a timing cover crank seal. Quote Link to comment Share on other sites More sharing options...
Mike Brichta Posted January 22, 2019 Share Posted January 22, 2019 I'm pretty sure that you will also have to remove the speedo cable and gear before removing the tail shaft. That also has an "O" ring around it. Can anyone else verify that? Thanks!! Mike Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted January 22, 2019 Share Posted January 22, 2019 Only the speedo cable is necessary. You could remove the gear housing if you wish but is not necessary. Quote Link to comment Share on other sites More sharing options...
ChrisM Posted January 22, 2019 Author Share Posted January 22, 2019 Awesome, thanks everyone or the info!!! I've got some work ahead of me this spring! Quote Link to comment Share on other sites More sharing options...
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