TH400 needs help

[85k10383]

With my new engine finally up and running strong, it has come to my attention that the trans needs some attention. Firstly, I am not sure if I have the modulator hooked up to the correct port on the front of the carb.

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By null at 2010-08-23
The modulator line is the little skinny thing that is going into the carb to the right of the PCV hose in the picture. There are two ports one is "timed" with vacuum at idle. The other is "untimed" with no vacuum at idle I believe I have the line attached to the "untimed" side. Now the problem, the trans absolutely WILL NOT kickdown, for any reason Does the modulator govern this or do I need to look at another component? Also, would an adjustable modulator serve any real purpose? The trans shifts fine BTW, it just won't drop out of gear for passing etc. Thanks in advance guys!
Ross
PS The only things I have done to the tranny is add a B&M +2 quart pan, and fill it with Jegs "Trick Shift" fluid. The TC I have no idea what it is, but it is slow and slushy, like stock.

 

[nvrenuf]

Kickdown on a th400 is controlled by a switch on the gas pedal bracket, the modulator does not control this function.

 

[85k10383]

Fascinating! I didn't know that, would LMC have the little bugger, or would I be better off going to my local NAPA? I don't suppose you could tell me where it attaches to the tranny could you? Thanks for the info BTW!

 

[GothRod]

In Car Craft magazine they suggested using the microswitch they sell in Summit or Jegs for nitrous activation for the kickdown if you have an aftermarket carb or lost the clunky stock piece.

A quick search on Summit pulled this up....

http://www.summitracing.com/search/?keyword=nitrous switch edelbrock&dds=1

Oh, and you do have the vaccum line hooked up right BTW lol

-John

 

[85k10383]

Well I'm glad i asked! I don't think the PO ever hooked up anything to handle kickdown at all! Its a damn good thing the new motor makes a goodly amount of torque. Still I would like to be able to get on the highway in some gear other than third LOL I need more info on how this system was supposed to work originally, ie, where it was powered from, where it connects to the trans etc.....
Update: I went in search of a bolt on solution as my misadventures with the dashboard have shaken my faith in my abilties at wiring. Found a kit from Lokar that should work perfectly for 75 bux.

 

[HotRodPC]

Have you got this resolved yet??? I just happened to be getting ready to post a thread in this section and seen your problem. Its a piece of cake. It is an electronic kickdown switch and your trans probably has it already. Look for an orange wire under the truck somewhere. But wait, if this was not an original T400 truck, it won't have it, so you'll have to wire it in yourself, still not hard to do. Here is a pic of the kickdown switch on the driver side of the trans, so you know the location of it. It should be a single spade.

 

[HotRodPC]

Here are some pics of the gas pedal kickdown switch. This switch is to be wired to the switch on the transmission. Pic #1 shows the left side of the switch where the wiring goes. Pic #2 shows how the switch mounts to the gas pedal assembly bracket. Pic #3 although blurry, will show you how it function. I think what I'd probably do, if you have a Pull a Part. Go to a pull a part and look for a 3/4 or 1 ton truck since most of them has Turbo 400's. There you should be able to rob the switch and possibly even the harness that goes from the switch to the trans. If not, just get the switch from a parts store install and wire it in yourself.

 

[85k10383]

Thank you for the pics and info^^!! Heres the funny thing, the truck was originally a 305/700r4. The PO bought it after the 350/TH400 swap and never touched anything with the tranny. The switch is there on the gas pedal, and the single spade connection on the tranny is present as well. I can't figure out why in the world you would go through all the trouble to swap out a motor and trans and not finish wiring it up like that! I am going to use the Lokar or Jegs kit since that will free me from worry about the wiring aspect of it. And no I haven't done it yet, the mad money fund got eaten alive by other things recently....

 

[HotRodPC]

Thank you for the pics and info^^!! Heres the funny thing, the truck was originally a 305/700r4. The PO bought it after the 350/TH400 swap and never touched anything with the tranny. The switch is there on the gas pedal, and the single spade connection on the tranny is present as well. I can't figure out why in the world you would go through all the trouble to swap out a motor and trans and not finish wiring it up like that! I am going to use the Lokar or Jegs kit since that will free me from worry about the wiring aspect of it. And no I haven't done it yet, the mad money fund got eaten alive by other things recently....

Believe it or not, if you got both switch, one at the pedal, and the on the trans, save yo money and just buy you a roll of wire and do it yourself. I do believe, all you'll do it go from an ign HOT wire off your fuse box which is just about a foot away on the other side of the steering column, to one side of the pedal switch, then another wire from the other side of the pedal switch to the single spade on the drive side of trans, and you are in bidness. That's all there is to it. I sure wouldn't spend no $40 for the Lokar kit if you have the pedal switch already in place. A roll of wire couldn't be more than $3-$4 depending on the guage and amount. I'd think 16 or 18guage wire would do the trick. It doesn't have to be real heavy.

 

[85k10383]

Hell I've got plenty of wire, I just figured there was some kind of magic "kick-down gennie" inside those little boxes they sell! I will give it a shot this coming weekend and see what happens. Thanks again!

 

[HotRodPC]

Nope, all you are wanting to do is wire that gas pedal switch, so that when you nail it, it activates the solenoid inside the pan near the valve body. That is the majic when the solenoid is activated it pushes a valve. I have even seen a guy put his to a push button switch also, so he didn't have to go full throttle to activate it. I guess whatever works, but if you are gonna do that, may as well just manually hit 2nd gear. Cuz my truck has such talls gears, 3.21's. My kickdown will go all the way down to first gear. So lets say I am coming up on a service rd to an on ramp for the freeway at 35-40mph, then I nail it to get on the highway, then it drops into first, and will stay there unitl 55mph then go to 2nd, if I keep it to the floor, and if I still keep it to the floor, it won't go into 3rd until something over 85. Maybe 90, I dunno for sure since the speedo quits at 85, buts its right there close to 85 or just over before it will hit 3rd. You'll sure like you truck alot better with it hooked up. What I don't like, is you have to go full throttle to get it to hit. I like the Turbo 350 cable better. I think it does a better job and is more adjustable. Now I have also been told the gas pedal switch is adjustable, and I should check into that, but I am actually OK the way it is, I am used to it now. There are just time when I'd like to go half throttle pick up a little speed and have drop into 2nd to get it there, but no, gotta go full throttle then instead of gradually gaining speed, you gain it quick and waste a gallon of fuel in a 454. Not you have need it, but here is a pic of that magic solenoid that is inside the pan. You can see the wire where it goes to the plastic switch inside the pan, and then of course that is where the spade is for your kickdown on the outside of the trans.