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stingray_76

11-11-2013 08:32 PM

What is this?

What is this? Why was it unplugged? Do I need it? Does it explain why my turbo 400 tranny won't downshift at WOT? What colour wires should be looking for to connect it?
Got an 87 1/2 ton with a 305 tbi.

http://i938.photobucket.com/albums/a...ps595813c7.jpg

beamn7

11-11-2013 09:21 PM

Re: What is this?

Yep! That is the kickdown switch for a THM-400 One side should have key hot power, the other side should get power when the gas pedal is fully depressed, sending power to the single spade connector on the side of the transmission which engages the kickdown solenoid inside the trans.

stingray_76

11-11-2013 09:53 PM

Re: What is this?

What colour are the wires for the original connection in the cab?
And if I have this, why do I have a vac modulator on the RH side of the tranny?

willett

11-11-2013 10:19 PM

Re: What is this?

Orange and white I think

4x4k30

11-11-2013 10:35 PM

Re: What is this?

Quote:

Originally Posted by stingray_76 (Post 6359217)

What colour are the wires for the original connection in the cab?
And if I have this, why do I have a vac modulator on the RH side of the tranny?

that is the kickdown switch for the turbo 400 i think it has red and white wire ran to it.. the wire that goes down to the transmission is orange. if you dont have a turbo 400 you dont need it.. the turbo 350 and 400 both have a vacum modulator thats what causes it to shift .

beamn7

11-12-2013 01:09 AM

Re: What is this?

THM-400 uses an electric kickdown whereas the THM-350 uses a detent cable aka kickdown cable. Both transmissions use a vaccum modulator as noted by 4X4k30, a modulator has more control over upshifts. Wire it back up and you will have downshifts again.

KQQL IT

11-12-2013 01:19 AM

Re: What is this?

Pull the shifter down. Isn't required.

ironroad9c1

11-12-2013 11:34 AM

Re: What is this?

yea the arm on my pedal won't even reach my kickdown switch.

stingray_76

11-13-2013 10:51 PM

Re: What is this?

I can't find the harness in the cab for the kickdown switch for the life of me.
The tranny still had the harness end with orange wire attached. Was only about 6" long. Found what I believe is the other end cut off up on the fire wall. Ran new wire to connect the 2 ends.
Where should I be looking in the cab?!
I'd really like to get this thing working. Truck is gutless and terrible on fuel.....:waah:

4x4k30

11-13-2013 11:26 PM

Re: What is this?

Quote:

Originally Posted by stingray_76 (Post 6362749)

the switch is located rite around on top of the accelerator foot pedal inside the cab. but it could be gone or your truck may have not had a turbo 400 in it and it was swaped in. and really this switch is just for it to go into passing gear it doest control the shifting. it only kicks in at full throttle ,

stingray_76

11-13-2013 11:47 PM

Re: What is this?

The switch was there, but absolutely no wiring for it. At least not any I can find.
Where would the wiring typically be?

4x4k30

11-13-2013 11:55 PM

Re: What is this?

Quote:

Originally Posted by stingray_76 (Post 6362822)

The switch was there, but absolutely no wiring for it. At least not any I can find.
Where would the wiring typically be?

i will look on my 79 tomorrow and see what i can find out for you

4x4k30

11-15-2013 04:34 PM

Re: What is this?

1 Attachment(s)

Quote:

Originally Posted by 4x4k30 (Post 6362835)

i will look on my 79 tomorrow and see what i can find out for you

here is a pic of the wires going to it. they are orange and pink with black stripe

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