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Discussion Starter · #1 ·
Long standing issues with a non-op TH400 kickdown switch (the one on the gas pedal assembly).

Already replaced the assumed faulty original switch with a new one when I had my old TH400 in
Then I replaced the transmision with a new TH400

Thought that between those 2 things I'd have a functioning kickdown. I've tested the switch "manually" by engaging it with my hand while driving. Nothing, so the issue is not with mounting.

Likely not the switch itself (replaced) or the electric solenoid in the trans (low odds of 2 units being both bad in 2 transmissions).

It is a simple 2 wire system (right?) where the switch completes the circuit. The wire from the switch to the trans is fine. The other wire to the power source at the panel looks fine. The harness connector looks fine.

So what do I check next?
 

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I have had a bad switch right out of the repop box. Took it apart to find it missing some guts that would make it function. Second one sent was fine.

You can bench test the switch with a multi meter (on continuity setting) or a battery, jumper wires, & and test light.

Make sure you are getting power to the switch from your wiring harness. If so, you could check for power on the switch terminal going to the transmission when the switch plunger is activated. This test would take the place of the multimeter or test light bench test. Note: these switches are self adjusting, but they have to be set up upon installation to self-adjust, I think.

There is a down shift solenoid in the transmission that could be bad. IIRC it is grounded inside the transmission by a short wire if it is a one wire solenoid. Solenoid could be bad or not grounded.
 

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Discussion Starter · #3 ·
I have had a bad switch right out of the repop box. Took it apart to find it missing some guts that would make it function. Second one sent was fine.

You can bench test the switch with a multi meter (on continuity setting) or a battery, jumper wires, & and test light.

Make sure you are getting power to the switch from your wiring harness. If so, you could check for power on the switch terminal going to the transmission when the switch plunger is activated. This test would take the place of the multimeter or test light bench test. Note: these switches are self adjusting, but they have to be set up upon installation to self-adjust, I think.

There is a down shift solenoid in the transmission that could be bad. IIRC it is grounded inside the transmission by a short wire if it is a one wire solenoid. Solenoid could be bad or not grounded.
Thanks man. I seriously doubt that 2 switches and 2 solenoids are bad, but who knows!

I suspect an issue in wire continuity and will test the circuit at the solenoid.

Several folks have told me these are "self adjusting" but I cannot for the life of me see how that can be. it just screws the the pedal brace and slides back to engage the circuit when the pedal is to the metal. I usually put a piece of vacuum tube on the switch shaft to make it engage quicker, but know of no other adjustment than that. Please LMK if I'm wrong!
 

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Cameo Ivory 1967
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One thing t o note, and I'll do some investigating in a bit... I believe there was a change in 67, so the switches dont adjust the same, which could definitely affect the activation. It happened to me and I found out that I bought a switch for a later year.

Dont quote me on this.
 

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Discussion Starter · #7 ·
Not sure my switch is the same one in the diagram.

The one in the diagram looks like a switch box with a shaft that moves back and forth in it. You appear to push it all the way forward (toward the engine), then use the gas pedal to "set" activation depth when pished all the way down. I get that.

My switch is sliding switch with a shaft that protrudes perpendicularly from the switch that engages the pedal. There is no adjutability to it. Here is the thread for the one I bought and installed:


do I have the wrong switch? Or am I somehow botching this simple procedure
 

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You cannot see the protrusion on the switch in the diagram, but it's there. I do NOT see a '66 kickdown switch listed in Ames' catalog. They have the 64/65 and the 67-77, but no '66. Makes me wonder what you have going on. Ames does say that the 67-77 switch "will also work in 1966 2-speed applications". No mention of the th400. It makes me grumpy when the stars don't align when researching old car parts. I don't see why your switch won't work with your set-up. Check for power and continuity and we can go from there.

They are self adjusting. They are meant to send power to the kickdown solenoid at WOT. You can cheat it my only giving it partial pedal, but as soon as you give it full pedal, it adjust to that. Adding a piece of hose to the nub will not work since it will readjust the next time under WOT. The problem with that is if the hose cheat takes the switch to it's travel limit before WOT...it will be the switch trying to stop you from reaching WOT. This will end up keeping you from giving full throttle and eventually break the switch.

You could wire up a positive wire to a toggle switch, then to the wire going to the solenoid and test it on the road. The reason our kickdown system does not allow higher speed kickdowns is because the transmission knows not to downshift at too high of an RPM. It's a conservative limit built in the transmission. Don't ask me how it works, it just does.

I can remember in my youth trying to down shift manually when it was not appropriate, meaning higher RPM's, and the transmission would not do it until I slowed down, then if would downshift to the gear the selector was in. If there is any proof that the 400TH is a great transmission...it's the way I treated it in my teens.
 

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Cameo Ivory 1967
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I was wondering about that too. My info was from a later year, but was the only bit that I could find.
It does specifically list 69 and up, so one would assume that there is a 67-68 switch out there somewhere...

Ames lists this one for 66-77, specifically stating that it worked for the 2 speed in 66, however... it seems contradictory to me that one switch covers 66-77, and another covers 69-72.

The mere fact that this issue exists, leads me to believe that we need to investigate.
 

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Cameo Ivory 1967
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Not sure my switch is the same one in the diagram.

The one in the diagram looks like a switch box with a shaft that moves back and forth in it. You appear to push it all the way forward (toward the engine), then use the gas pedal to "set" activation depth when pished all the way down. I get that.

My switch is sliding switch with a shaft that protrudes perpendicularly from the switch that engages the pedal. There is no adjutability to it. Here is the thread for the one I bought and installed:


do I have the wrong switch? Or am I somehow botching this simple procedure
So... am I to assume that after all this crap, it's still not downshifting?
 

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I'm reaching for other reasons for ylwgto 's the non-functioning kickdown I guess...

I assume he has the 66 2 speed kickdown bracketry by the go-pedal and using a later model switch. I have to question the mounting geometry. I would still perform all the circuitry testing to verify the parts being used...then tackle the location of the switch and how it operates. Some slight mods may be needed to correct its mounted position, but I doubt it since Ames says that the 67 and up switch will work with the 2 speed auto. I'm still putting my money on a short somewhere or...

Some 400TH transmissions had 2 wire connections, one for kickdown and the other for something else (I think something to do with the emission's TCS system). Maybe the kickdown wire is connected to the wrong spot at the transmission.


Font Auto part Sharing Event Rectangle


This is all my Ames catalog shows for kickdown switched, but it is a couple years old.
 

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Here's the connector at the transmission for the 2-wire set-up. You cannot see it on the left side, but there are two connections on both sides. Not only could the wire be on the wrong pin outside the transmission, but it could be wrong inside (and/or).

Automotive tire Automotive lighting Rim Automotive wheel system Auto part

Something to be aware of if the circuitry tests go well. Is the solenoid even hooked up in there?
 

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I'm reaching for other reasons for ylwgto 's the non-functioning kickdown I guess...

I assume he has the 66 2 speed kickdown bracketry by the go-pedal and using a later model switch. I have to question the mounting geometry. I would still perform all the circuitry testing to verify the parts being used...then tackle the location of the switch and how it operates. Some slight mods may be needed to correct its mounted position, but I doubt it since Ames says that the 67 and up switch will work with the 2 speed auto. I'm still putting my money on a short somewhere or...

Some 400TH transmissions had 2 wire connections, one for kickdown and the other for something else (I think something to do with the emission's TCS system). Maybe the kickdown wire is connected to the wrong spot at the transmission.


View attachment 156116

This is all my Ames catalog shows for kickdown switched, but it is a couple years old.
If it has two tabs on the one connector at the TH400, the other tab is for a switch pitch torque converter, but those are pretty rare these days. That could be a bonus if you have all the parts installed. If that's the case, let me know and I will try to help you out.

Otherwise, a switch that completes the circuit is all you need. If have ignition key to run but engine not running and you manually move the switch, do you hear a faint click from the transmission?
 

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It would be helpful to know the year of your transmission and other nameplate data as to what car it came out of. The nameplate is on the passenger side.
Later T400s have the VIN on the drivers side pan rail.
Also be helpful if it has the two terminal connector on the drivers side or one.

Early Buicks and Olds had the switch pitch converter and it did have a two terminal connector. That was phased out and the single terminal became standard. In 1970, the two terminal connector came back, one terminal for KD, the other for the distributor vacuum solenoid.
Internally the terminal for the KD goes to a solenoid which alters the oil flow to enable a lower gear but only if certain conditions are met. Depending on how your 400 is calibrated those conditions could prohibit KD above 60 mph.
Internally the second connector terminal for the distributor vacuum solenoid ground is controlled by a switch that closes to ground in 3rd gear. If the wires were mixed up, when the transmission shifted to third, it would blow the fuse for the kick down circuit.

There are numerous ways to approach this problem.
1. Test light or meter; Check for voltage at the kick down switch. 1966 Tempest models had two Orange wires at the switch. One comes from the wiper fuse at the top, the other goes to the firewall connector and then to the transmission.
With the ignition ON, engine not running, you should have 12 volts on one terminal. Place the meter lead to the second terminal, and press the accelerator to WOT. It should show 12 volts at WOT. If not, then your problem is in the switch. Try moving the switch actuator arm manually and check for voltage.

2. If the switch checks out, pull the terminal cap off the transmission connector. Insert meter lead inside the terminal cap and check voltage again, helps to have a helper to push the accelerator to WOT. If you have voltage then you have a bad or miswired solenoid. No voltage means there is an open in the wire between the accelerator and transmission. Possibly the firewall connector.

3. A final check would be is to take a long jumper wire from the positive battery to the transmission connector terminal. Touch the transmission terminal and listen for a click. If it clicks, solenoid is good. if not...
 

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It would be helpful to know the year of your transmission and other nameplate data as to what car it came out of. The nameplate is on the passenger side.
Later T400s have the VIN on the drivers side pan rail.
Also be helpful if it has the two terminal connector on the drivers side or one.

Early Buicks and Olds had the switch pitch converter and it did have a two terminal connector. That was phased out and the single terminal became standard. In 1970, the two terminal connector came back, one terminal for KD, the other for the distributor vacuum solenoid.
Internally the terminal for the KD goes to a solenoid which alters the oil flow to enable a lower gear but only if certain conditions are met. Depending on how your 400 is calibrated those conditions could prohibit KD above 60 mph.
Internally the second connector terminal for the distributor vacuum solenoid ground is controlled by a switch that closes to ground in 3rd gear. If the wires were mixed up, when the transmission shifted to third, it would blow the fuse for the kick down circuit.

There are numerous ways to approach this problem.
1. Test light or meter; Check for voltage at the kick down switch. 1966 Tempest models had two Orange wires at the switch. One comes from the wiper fuse at the top, the other goes to the firewall connector and then to the transmission.
With the ignition ON, engine not running, you should have 12 volts on one terminal. Place the meter lead to the second terminal, and press the accelerator to WOT. It should show 12 volts at WOT. If not, then your problem is in the switch. Try moving the switch actuator arm manually and check for voltage.

2. If the switch checks out, pull the terminal cap off the transmission connector. Insert meter lead inside the terminal cap and check voltage again, helps to have a helper to push the accelerator to WOT. If you have voltage then you have a bad or miswired solenoid. No voltage means there is an open in the wire between the accelerator and transmission. Possibly the firewall connector.

3. A final check would be is to take a long jumper wire from the positive battery to the transmission connector terminal. Touch the transmission terminal and listen for a click. If it clicks, solenoid is good. if not...
Thanks for the education on the later TH400s. I never knew they did a second terminal for a distributor vacuum solenoid. Was that to advance timing as it downshifted with the kickdown activation?
 
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