55.2-59 Turbo 400 kick down question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

toymanbob · 09-30-2024, 11:28 PM

I've found a wire attached to the trans and assume it's related to kick-down. Is it triggered by 12V and from where? Bob

**mr48chev** · 09-30-2024, 11:52 PM

Best idea is to check the wiring diagram for the donor rig. Or search out Turbo kick down switch or passing gear switch.

dsraven · 10-01-2024, 09:20 AM

turbo 400 has an electric switch activated by the accel pedal inside the cab normally. it is 12v fused supply from a "hot with key in run" fuse box connection. just google the topic for a few images of what the switch normally looked like and what the aftermarket hotrod suppliers are supplying.

**mr48chev** · 10-01-2024, 08:24 PM

The switch can be inside the cab connected to the gas pedal or on the throttle linkage at the carb.

https://www.ebay.com/itm/12598909698...G090XKZ6B0HAFJ

https://www.ebay.com/itm/13467992884...YaAizlEALw_wcB

The switch for the Edelbrock carb would probably be the simplest to hook up on a truck. The other switch goes on the throttle pedal assembly and you pretty well have to use the whole assembly.

The style in the photo was used on Oldsmobiles a lot but you have to have the lever on the carb designed for it.

dsraven · 10-01-2024, 10:31 PM

It's a simple switch. There are lots of variations you could use. Back in the day as a heavy duty mechanic Mack trucks used a simple micro switch on the linkage in order to operate the Jake brake. It had a built in diode to stop reverse power flow from energy developed when the magnetic fields collapsed in the Jake actuator solenoids

dsraven · 10-01-2024, 10:39 PM

this is what they looked like just for reference. a switch similar to this could be easily placed on the throttle linkage so that the kickdown would operate properly. not necessarily this switch but you get the idea

https://www.ebay.com/p/2099396414

here is a thread that discusses the kickdown switches. it is interesting that some are operated by a chain that lookslike a tub drain plug chain. whatever works and has longevity I guess. i seem to remember Ford had a similar set up

https://67-72chevytrucks.com/vboard/...d.php?t=679916

**mr48chev** · 10-01-2024, 11:31 PM

Ebay sellers are nuts on used OEM Chevy kick down switches. Only for the restorer shooting for a 100 point car.

Personally I'd look into the 30 something buck micro switch. I may have to get one of those for my 71 GMC with the Cad 500 in it. I want to get it running and driving before winter.

1project2many · 10-02-2024, 08:54 AM

With a BBC installed, it seems like someone must have replaced the original gas pedal with one from another vehicle? Here's a square body truck gas pedal with a THM 400 kickdown switch. The switch is near the top of the picture. It's the tan parts.

This one is for sale for $25 from a guy in PA.
https://www.hillbillywizard.com/cucv...bly-for-th400/

If you use a microswitch or other low current device you might want to consider using a relay to go with it.

If you have a column mounted dimmer switch you could use the old floor switch to control kickdown. I have done this and it can be nice to force downshift at light throttle for a little help accelerating or going uphill.

Loving the heater bypass hose.

09-30-2024, 11:28 PM	#1
toymanbob Registered User Join Date: Aug 2020 Location: Grants Pass Or Posts: 39	Turbo 400 kick down question I've found a wire attached to the trans and assume it's related to kick-down. Is it triggered by 12V and from where? Bob Attached Images Last edited by Rickysnickers; 10-01-2024 at 08:59 AM.

09-30-2024, 11:52 PM	#2
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 15,633	Re: Turbo 400 kick down question Best idea is to check the wiring diagram for the donor rig. Or search out Turbo kick down switch or passing gear switch. __________________ Founding member of the too many projects, too little time and money club. My ongoing truck projects: 48 Chev 3100 that will run a 292 Six. 71 GMC 2500 that is getting a Cad 500 transplant. 77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around.

10-01-2024, 09:20 AM	#3
dsraven Registered User Join Date: Nov 2010 Location: calgary alberta Posts: 8,185	Re: Turbo 400 kick down question turbo 400 has an electric switch activated by the accel pedal inside the cab normally. it is 12v fused supply from a "hot with key in run" fuse box connection. just google the topic for a few images of what the switch normally looked like and what the aftermarket hotrod suppliers are supplying.

10-01-2024, 08:24 PM	#4
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 15,633	Re: Turbo 400 kick down question The switch can be inside the cab connected to the gas pedal or on the throttle linkage at the carb. https://www.ebay.com/itm/12598909698...G090XKZ6B0HAFJ https://www.ebay.com/itm/13467992884...YaAizlEALw_wcB The switch for the Edelbrock carb would probably be the simplest to hook up on a truck. The other switch goes on the throttle pedal assembly and you pretty well have to use the whole assembly. The style in the photo was used on Oldsmobiles a lot but you have to have the lever on the carb designed for it. Attached Images __________________ Founding member of the too many projects, too little time and money club. My ongoing truck projects: 48 Chev 3100 that will run a 292 Six. 71 GMC 2500 that is getting a Cad 500 transplant. 77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around. Last edited by mr48chev; 10-01-2024 at 08:33 PM.

10-01-2024, 10:31 PM	#5
dsraven Registered User Join Date: Nov 2010 Location: calgary alberta Posts: 8,185	Re: Turbo 400 kick down question It's a simple switch. There are lots of variations you could use. Back in the day as a heavy duty mechanic Mack trucks used a simple micro switch on the linkage in order to operate the Jake brake. It had a built in diode to stop reverse power flow from energy developed when the magnetic fields collapsed in the Jake actuator solenoids

10-01-2024, 10:39 PM	#6
dsraven Registered User Join Date: Nov 2010 Location: calgary alberta Posts: 8,185	Re: Turbo 400 kick down question this is what they looked like just for reference. a switch similar to this could be easily placed on the throttle linkage so that the kickdown would operate properly. not necessarily this switch but you get the idea https://www.ebay.com/p/2099396414 here is a thread that discusses the kickdown switches. it is interesting that some are operated by a chain that lookslike a tub drain plug chain. whatever works and has longevity I guess. i seem to remember Ford had a similar set up https://67-72chevytrucks.com/vboard/...d.php?t=679916

10-01-2024, 11:31 PM	#7
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 15,633	Re: Turbo 400 kick down question Ebay sellers are nuts on used OEM Chevy kick down switches. Only for the restorer shooting for a 100 point car. Personally I'd look into the 30 something buck micro switch. I may have to get one of those for my 71 GMC with the Cad 500 in it. I want to get it running and driving before winter. Attached Images __________________ Founding member of the too many projects, too little time and money club. My ongoing truck projects: 48 Chev 3100 that will run a 292 Six. 71 GMC 2500 that is getting a Cad 500 transplant. 77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around.

10-02-2024, 08:54 AM	#8
1project2many Registered User Join Date: Mar 2012 Location: Lakes Region NH Posts: 3,189	Re: Turbo 400 kick down question With a BBC installed, it seems like someone must have replaced the original gas pedal with one from another vehicle? Here's a square body truck gas pedal with a THM 400 kickdown switch. The switch is near the top of the picture. It's the tan parts. This one is for sale for $25 from a guy in PA. https://www.hillbillywizard.com/cucv...bly-for-th400/ If you use a microswitch or other low current device you might want to consider using a relay to go with it. If you have a column mounted dimmer switch you could use the old floor switch to control kickdown. I have done this and it can be nice to force downshift at light throttle for a little help accelerating or going uphill. Loving the heater bypass hose.



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