What's this?

[OUbesto]

I came across this switch sitting on top of my TH400. It has two red wires attached with two empty posts and has a plunger on the end. I'm thinking it might an old kickdown that was used on the OE carb. PO installed updated 4bbl Holley electric choke model. One of the red wires attached to the switch is connected to a male lead on the tranny. Is this switch even necessary anymore? Is red wire to tranny necessary?

[bill3rail]

Neutral Safety Switch????

[100%Chevy]

It is a kick-down switch(passing gear).The other wire should go to 12 volts positive at the fuse panel.
You need it if you want your passing gear to work.
Mike.

[FirstOwner69]

It may be a kick-down switch, but is not a factory kick-down for a TH400. 67-70s with a rod carb linkage used a switch mounted with the carb. 71s and 72s with the cable carb linkage used a switch inside the cab actuated by the accelerator linkage. It's probably a homegrown or aftermarket switch to work with your Holley.

[AussieinNC]

Its the kick down switch that mounts to the carb...have seen these on various factory 4 BBL's...

Most of the mods I do with these is to mount a push button on the shift lever...and wire it thru to the male terminal on the trans...

Anytime you need passing gear, push the button and the gas pedal...release the button to allow trans to shift back up again.

[FirstOwner69]

Originally Posted by AussieinNC

Its the kick down switch that mounts to the carb...have seen these on various factory 4 BBL's...

Most of the mods I do with these is to mount a push button on the shift lever...and wire it thru to the male terminal on the trans...

Anytime you need passing gear, push the button and the gas pedal...release the button to allow trans to shift back up again.

Interesting. I've never seen one like that on this generation of truck with TH400s. Is that an original installation on one of our trucks? Here's a picture of the original from my 69.

[OUbesto]

Im not sure if it was an original equipment install. I do have a vacuum line that is connected to the passenger side of the tranny and runs directly from the manifold. Since PO replaced original 4 bbl carb with Holley and did not hook up this switch, my assumption is that I don't need it anymore, right? Assuming I do not need this switch anymore, then I'm wondering if the red wire connected from the switch to the tranny is necessary. Can anyone shed some light?

PS - I'm getting ready to do a complete re-wire and I'm trying to sort out what's old, what's new etc..

[OUbesto]

Originally Posted by 100%Chevy

It is a kick-down switch(passing gear).The other wire should go to 12 volts positive at the fuse panel.
You need it if you want your passing gear to work.
Mike.

Thanks Mike for your reply. So is it the electrical connection that engages the "passing gear" in the tranny? I'm assuming it must be since the plunger no longer functions by just hanging on top of the tranny.

[100%Chevy]

Originally Posted by OUbesto

Thanks Mike for your reply. So is it the electrical connection that engages the "passing gear" in the tranny? I'm assuming it must be since the plunger no longer functions by just hanging on top of the tranny.

Yes,there's solenoid in the trans that engages the passing gear.
The TH-400 was originally introduced in 1965.GM has used it on most all their products since.That switch was used on all until later when a different version was added to the throttle pedal.
Also,on a TH-400,that vacuum hose to the modulator isn't for the passing gear like you find on TH-350 and others.
Mike.

[OUbesto]

Originally Posted by 100%Chevy

Yes,there's solenoid in the trans that engages the passing gear.
The TH-400 was originally introduced in 1965.GM has used it on most all their products since.That switch was used on all until later when a different version was added to the throttle pedal.
Also,on a TH-400,that vacuum hose to the modulator isn't for the passing gear like you find on TH-350 and others.
Mike.

Thanks Mike for your reply and information. So when I do my re-wiring, should I eliminate the kickdown switch since it is not connected to anything?

[100%Chevy]

Yes,you can eliminate it.
But,I would save it as you may find you need it later on down the road.
Mike.

[AussieinNC]

I would personally recommend you keep the kick down function available, and perhaps either move the function to a later model pedal mounted style or, as I mentioned in my previous response, place a press button on the gear stick to enable the passing gear solenoid...(aka Kick down solenoid).

It is not that hard to do, especially if you are doing re-wiring etc...

To wire a manual kick down button, you will need an ignition hot power source, fused of course, to the press button, out from the press button to the kick down solenoid fitting on the side of the transmission. When the truck is driving, pressing the button down will engage the solenoid, dropping the trans into 2nd or 1st, depending on the road speed at the time.

[CG]

Originally Posted by AussieinNC

place a press button on the gear stick to enable the passing gear solenoid...(aka Kick down solenoid).

. When the truck is driving, pressing the button down will engage the solenoid, dropping the trans into 2nd or 1st, depending on the road speed at the time.

Make a little label that says NOS next to the switch and make sure the switch actuator is blue ... fool your friends.

[71CHEVYSHORTBED402]

If I recall, the 71-72 used the electric kick down that runs from RADIO on the fuse box to the gas pedal, and from the gas pedal to the what-u-call-it at the transmission. Maybe it's a solenoid. I've heard it referred to as a "pass through". The "solenoid" may be one or two prongs. Two prong is for kick down and TCS. My 71 had two prong, but I'm eliminating the TCS, it's worthless.

Prior to 71, I believe they used what you've got. I'm not aware of the configuration however.

[OUbesto]

Originally Posted by 71CHEVYSHORTBED402

If I recall, the 71-72 used the electric kick down that runs from RADIO on the fuse box to the gas pedal, and from the gas pedal to the what-u-call-it at the transmission. Maybe it's a solenoid. I've heard it referred to as a "pass through". The "solenoid" may be one or two prongs. Two prong is for kick down and TCS. My 71 had two prong, but I'm eliminating the TCS, it's worthless.

Prior to 71, I believe they used what you've got. I'm not aware of the configuration however.

Tony,
The red wire from the kickdown switch is connected to one of the two male prongs on the tranny. I haven't traced the red wire from the "KD" switch to see where it originates. I'll do that this weekend.

[AussieinNC]

My friends usually dont notice anything other than the blower whine...and the force of being pushed back in their seats...after the first time, they usually ask me not to use the button...

I cant imagine what NOS and a 6-71 together would result in, other than more dollars out of this old mans pocket...

[71CHEVYSHORTBED402]

Originally Posted by OUbesto

Tony,
The red wire from the kickdown switch is connected to one of the two male prongs on the tranny. I haven't traced the red wire from the "KD" switch to see where it originates. I'll do that this weekend.

I believe it's supposed to be orange. Here are my notes on it, for whatever they're worth:



Switch mounting: The kick down switch mounts to the accelerator bracket using one 3/8" notched tipped screw. The screw thread is 1/4" x 5/8". The screw inserts from the RH (TS). The switch plate has two tabs that insert into holes in the accelerator bracket from the RH (TS). The two pins for the connector are on the lower side of the switch. The pins face the LH (TS).

Kick down switch wiring: A two point connector (pink & orange) plugs into the kick down switch with the orange wire on top.

• Pink wire: This wire plugs into fuse box label "RADIO". A connector comes from the fuse box with a second pink wire, which is for the radio.

• Orange wire: The orange wire routes through the firewall using the same grommet as for the oil pressure line. The wire is above the oil pressure line (see oil line for correct positioning). This wire is in woven sheath to approx. 4" from the grommet in the engine compartment.

• The orange wire connector plugs into a second orange wire connector, which runs to the transmission boot connector. This wire uses two retainers spot welded (or riveted) to the firewall. One is located on the LH (TS) of the firewall pocket and the other is parallel below it.

A wire(s) retainer mounted on the transmission using a 1/4" head machine tap screw. The screw hole is approx. 6" from the end of the boot connector. The screw thread is #10 x 5/8".

NOTES:
For a two pin system (i.e., kick down & TCS), the vertical terminal on the transmission is for the kick down.

See Transmission Controlled Spark.

See this thread for the solenoid/pass through: http://67-72chevytrucks.com/vboard/s...d.php?t=730139

[OUbesto]

Tony, thank you so much for the great info. This is why I like this forum and its members!