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11-11-2013, 08:32 PM
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#1 |
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Registered User
Join Date: Oct 2013
Location: Huntsville
Posts: 5
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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. 
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11-11-2013, 09:21 PM
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#2 |
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Registered User
 Join Date: Oct 2011
Location: Wildomar, CA
Posts: 466
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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.
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11-11-2013, 09:53 PM
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#3 |
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Registered User
Join Date: Oct 2013
Location: Huntsville
Posts: 5
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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? |
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11-11-2013, 10:19 PM
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#4 |
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Another Day, Another Dollar
Join Date: Nov 2008
Location: North Vancouver, BC
Posts: 1,316
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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" 
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11-11-2013, 10:35 PM
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#5 | |
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Registered User
Join Date: Jun 2003
Location: ga
Posts: 630
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Re: What is this?
Quote:
__________________
4x4k30 if trouble was money i would have plenty |
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11-12-2013, 01:09 AM
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#6 |
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Registered User
Join Date: Oct 2011
Location: Wildomar, CA
Posts: 466
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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.
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11-12-2013, 01:19 AM
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#7 |
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At the body shop.
Join Date: Aug 2009
Location: Land of fruits and nuts.
Posts: 5,257
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Re: What is this?
Pull the shifter down. Isn't required.
__________________
" That didnt make it any newer " " Dont antique the equipment " |
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11-12-2013, 11:34 AM
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#8 |
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Master Hater
Join Date: Apr 2006
Location: Temple,Tx.
Posts: 402
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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 |
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11-13-2013, 10:51 PM
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#9 |
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Registered User
Join Date: Oct 2013
Location: Huntsville
Posts: 5
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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..... 
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11-13-2013, 11:26 PM
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#10 | |
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Registered User
Join Date: Jun 2003
Location: ga
Posts: 630
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Re: What is this?
Quote:
__________________
4x4k30 if trouble was money i would have plenty |
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11-13-2013, 11:47 PM
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#11 |
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Registered User
Join Date: Oct 2013
Location: Huntsville
Posts: 5
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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? |
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11-13-2013, 11:55 PM
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#12 | |
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Registered User
Join Date: Jun 2003
Location: ga
Posts: 630
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Re: What is this?
Quote:
__________________
4x4k30 if trouble was money i would have plenty |
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11-15-2013, 04:34 PM
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#13 | |
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Registered User
Join Date: Jun 2003
Location: ga
Posts: 630
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Re: What is this?
Quote:
__________________
4x4k30 if trouble was money i would have plenty |
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