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I got a th400 trans and Ive been told that the kickdown is activated either by vacuum or by an electrical switch. How can I tell which one I have. There is a tube which runs from the manifold to the trans, but there is also a little tab that sticks out on the drivers side right next to the speedo cable. When I floor it it doesnt kick down. which one do I have and if its the vacuum type how do I fix this problem. I know its alot but any help would be greatly appreciated! Thanks in advance!
 

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I always thought that all TH400s had electrical kickdown. I may be wrong. The vacume line you see is for the vacume modulator. It tells the trans. when to shift acording to how much vacume(how far the pedal is down). The electrical switch should be on the right side of the gas pedal. It mounts on a little bracket, so its not actuated until the pedal is down to the floor. The wire going to the trans. hooks up on the right lower side about 1/2 way back. Kickdown prob. could well be the switch. Just a little insight.
 

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All Turbo 400's use an electrical solenoid to control the kick-down. The connector is located on the driver's side of the transmission. When the solenoid is activated (12 volts), the line pressure also increases slightly resulting in a slightly higher rpm shift point. If your transmission still won't downshift (3rd to 2nd) when the switch is activated, then you may need to check the wiring in the transmission. Some people disconnect the wire inside the transmission during rebuilds since it is not required for racing purposes.
 

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The vacuum part of the picture also has to do with shift points; the higher the vacuum, the lower the shift point. The manifold vacuum port that this line is attached to has greater vacuum at idle, and decreases as acceleration increases. If you disconnected this vacuum line, your tranny would shift at high rpms, regardless of the amount of acceleration. Mine shifts from 1st to 2nd at about 40-45 mph when disconnected (use to have a problem keeping that line attached), whether I have my foot in it or not.
However, once the tranny has shifted, removing this vacuum would not cause it to downshift; if your doing 35 in third and disconnect the line, you're not going to all-of-a-sudden be in 1st or 2nd. You would have to slow way down before it would down shift.
 

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OK, the guy previous owner of my car didn't have the kickdown hooked up. I don't know if that was on purpose or not, he said he liked to shift manually. I was going to clean the switch, and the plastic disintegrated in my hands. I found a Skylark switch that I can easily modify to work.

Back to the solenoid, is it a bullet proof item? If I still have one in the trans, what is the probability it will still work after having been disconnected for 6 years? If I am laying under the car (not running) and jump 12V to the switch, will I be able to hear it click?

And back to vaccuum, mine has a pretty radical Lunati cam, will that affect shifting? It only has 7 in of vaccuum at idle.
 

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Theres not a whole lot to the solenoid, and I don't think non-use would hurt it. I don't think I would even consider messing with it until the switch/wiring is installed, and it still doesn't work. An easy test setup would be to run a toggle switch into the passenger compartment, wired to a 12v source(it should eventually go to the "IGN" terminal at the fuse block when you do the final installation) and the tranny. Get up to about 40 and flip the switch on. It should downshift.
Regarding getting under the car: I'm not sure if you will be able to hear it, but Fred (from Ontario) has suggested in the past that if you tune your AM radio to 1400, and activate the solenoid, that you should hear a "pop" on the radio.
I use to have a large cam in my car and it didn't effect it as far as I could tell.
 

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OK, I rolled under, and put 12V across the terminal lugs. I heard absolutely nothing, and I was inside my quiet garage. I did see tiny sparks jump as the test wires contacted the battery terminals. So there is something inside, and it's pulling a small current. I just wish I had heard a click.

So if the solenoid is fried or stuck, how deep in the tranny is it, how hard to replace? Can you still buy the solenoid?
 

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gibbons; you said that you put 12v across the terminals (plural?). If the tranny has two terminals then you have a th400 with the TCS switch and kickdown. I beleive the top terminal is the kickdown but not sure. You should only need to touch a 12v source to one terminal, ground is through the case of the tranny.

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Steve Strasemeier (70SS)
 

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I have a built TH400 in my 70 SS. It is also the 'switch-pitch' (Variable Stall) variety. Maybe there's a tranny guru out there that can tell us which terminal activates the kick-down, and which the torque converter. (One is verticle, the other horizontal) Thanks!
 

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I have 2 pictures one showing the connector for the variable pitch two connectors.One for the single spade connector the single is for the down shift and it is in the verticle position...FRED
 
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