What is this? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

stingray_76 · 11-11-2013, 08:32 PM

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.

beamn7 · 11-11-2013, 09:21 PM

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

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?

4x4k30 · 11-11-2013, 10:35 PM

Quote:

Originally Posted by stingray_76

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 .

willett · 11-11-2013, 10:19 PM

Orange and white I think

beamn7 · 11-12-2013, 01:09 AM

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

Pull the shifter down. Isn't required.

ironroad9c1 · 11-12-2013, 11:34 AM

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

stingray_76 · 11-13-2013, 10:51 PM

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.....

4x4k30 · 11-13-2013, 11:26 PM

Quote:

Originally Posted by stingray_76

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.....

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

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

Quote:

Originally Posted by stingray_76

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

Quote:

Originally Posted by 4x4k30

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

11-11-2013, 08:32 PM	#1
stingray_76 Registered User Join Date: Oct 2013 Location: Huntsville Posts: 5	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.

11-11-2013, 09:21 PM	#2
beamn7 Registered User Join Date: Oct 2011 Location: Wildomar, CA Posts: 466	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.

11-11-2013, 09:53 PM	#3
stingray_76 Registered User Join Date: Oct 2013 Location: Huntsville Posts: 5	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?

11-11-2013, 10:19 PM	#5
willett Another Day, Another Dollar Join Date: Nov 2008 Location: North Vancouver, BC Posts: 1,316	Re: What is this? Orange and white I think __________________ -78 K20 Cheyenne 454 long box, 4" lift, 35" MT's, '84 cab, '80 box "its hip to be square"

11-12-2013, 01:09 AM	#6
beamn7 Registered User Join Date: Oct 2011 Location: Wildomar, CA Posts: 466	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.

11-12-2013, 01:19 AM	#7
KQQL IT At the body shop. Join Date: Aug 2009 Location: Land of fruits and nuts. Posts: 5,257	Re: What is this? Pull the shifter down. Isn't required. __________________ " That didnt make it any newer " " Dont antique the equipment "

11-12-2013, 11:34 AM	#8
ironroad9c1 Master Hater Join Date: Apr 2006 Location: Temple,Tx. Posts: 402	Re: What is this? yea the arm on my pedal won't even reach my kickdown switch. __________________ 1997 C1500 ECSB 4.3/NV3500 8.5 3.42 "This evening, all of you bleeding hearts... why don't just go ahead and hug yourself for the next 20 minutes or so, because there's a really good chance you're gonna be offended".- Captain Owen Honors

11-13-2013, 10:51 PM	#9
stingray_76 Registered User Join Date: Oct 2013 Location: Huntsville Posts: 5	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.....

11-13-2013, 11:47 PM	#11
stingray_76 Registered User Join Date: Oct 2013 Location: Huntsville Posts: 5	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?



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.