Th 400 ¿?s/problems Help!!!!

Discussion in 'The Garage' started by primerk5, Jun 15, 2006.

  1. primerk5

    primerk5 1/2 ton status

    Jan 13, 2001
    Likes Received:
    Finksburg MD
    My friends Truck has a TH 400 Tranny It seemed to work fine before but now it won't shift out of second gear. The Module in the side went bad so we replaced it with a new one out of a TH 350. He was told that this would work because you could adjust a screw inside the vacume port. Now there is an oarnge wire on the driverside of the transmission. What is this for??? We changed cabs on the truck and It's not pluged in anymore. He swears to me it has never been pluged in since he got it. The wire comming from the cab was just hanging. Also when you do drive the truck and it gets to the top of second gear and you let off the gas it just coasts to a stop. You can do this in first gear also. The transmission dosen't go "against" the engine to slow the truck down like it normally would. It used to because thats how we slowed it down when the brakes were not working right when he first got it Before we changed the body.

    So my questions are
    1. What dose the Orange wire do and how can we hook it back up if we need it.
    2. Dose the TH 350 Module make a difference?
    3. What the heck is wrong with this thing.

    Thanks any help would be great. He's planning on taking this rat trap to Bloomsburg for the 4wheel jambo. We got to get this straightend out.
  2. onetonbb74

    onetonbb74 1/2 ton status Premium Member

    Dec 1, 2005
    Likes Received:
    Morgan Hill, CA
    orange wire: Kick down solenoid. hooks up to the switch on the gas pedal and the other wire off the switch goes to the fuse panel as accessory 12v hot.

    th350 vacumm module: same part number for th400 no difference

    wrong: who knows, mine goes into third but has no compression braking in 2nd gear at all (if you let off the gas, your in neutral). Also, the tranny lugs out of the hole sometimes like there is no power and sometimes its perfect. Id have to say a stuck valve body or an internal pressure leak. Mine was hooked to a blown motor when i got it in my truck so i ran it because it was in there already and now i need to pull it a year later.
  3. diesel4me

    diesel4me 1 ton status Premium Member

    Jul 24, 2003
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    could be...

    Is the modulator you swapped in GOOD?? might have had a blown diaphram too! sounds like the modulator when you say the tranny "coasts" when you let off the gas,that and not shifting into 3rd are the common symptoms of modulator failure,or loss of vacuum to it...are you sure vacuum is getting to the modulator??..maybe the hose fell off at the motor,or the steel tube rusted thru, or got kinked..

    Try manually shifting the tranny --shift into "low"then second,then move the lever into "drive" when you think it should shift on a test ride..if it goes into third then,its most likely a modulator problem...could be valve body troubles too..(sticky valve,or a blown gasket between the spacer plate and valve body..)..good luck.:crazy:

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