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  1. #1
    Master Mechanic rustyk2's Avatar
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    Question More transmission issues

    Hey guys, got the tranny to stop dumping fluid but now it developed a real problem. When it first starts up and I engage the tranny, it runs through the gears fine. After a few minutes it will drop from third to second. Can manually shift down, then slid the shifter to D and it shifts up then drops again. Think the bands toasted but not sure. Replaced the modulator valve and fluid and filter. Hope it can be saved, but do not hold out much hope.
    Thanks in advanced

    Dana Pelletier
    Dana South Carolina

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  2. #2

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    Quote Originally Posted by rustyk2 View Post
    Hey guys, got the tranny to stop dumping fluid but now it developed a real problem. When it first starts up and I engage the tranny, it runs through the gears fine. After a few minutes it will drop from third to second. Can manually shift down, then slid the shifter to D and it shifts up then drops again. Think the bands toasted but not sure. Replaced the modulator valve and fluid and filter. Hope it can be saved, but do not hold out much hope.
    Thanks in advanced

    Dana Pelletier
    A restricted vacuum line can cause this problem. Make sure the top hose at the intake manifold is not cracked ot pinched.
    Jim

    2004 SILVERADO 2500HD LS
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  3. #3
    Master Mechanic rustyk2's Avatar
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    Hi Jim, Tried cleaning out the steel line had some restriction, cleaned it out. replaced the rubber hose connections on the line but still same problem. Question, can you tighten or adjust the band? if so how and where. I heard the adjuster is under the pan by the valve body.
    I really appreciate the help.
    Thank You,
    Dana

  4. #4

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    Quote Originally Posted by rustyk2 View Post
    Hi Jim, Tried cleaning out the steel line had some restriction, cleaned it out. replaced the rubber hose connections on the line but still same problem. Question, can you tighten or adjust the band? if so how and where. I heard the adjuster is under the pan by the valve body.
    I really appreciate the help.
    Thank You,
    Dana
    Dana, Unfortunately your transmission's band has nothing to do with your problem. The THM 350 and THM 400 both have one band. The band is only used for engine braking in 2nd gear. You didn't say what trans you have but your problem is not the band. If your transmission is full of fluid it should engage immediately when shifted into gear. If it delays you either have a problem with the filter, restricted, missing o ring, etc, or the forward clutches are burned up. How did the pan look when you serviced it?

  5. #5
    Master Mechanic rustyk2's Avatar
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    Sorry about the lack of info. Have the th400. The fluid was medium dark, but not burnt smelling, the filter was really bad the magnet had the usual crap on it and some grit in the pan. no peices or chunks of gears or the like. I'm afraid the only cure is a rebuild. but any help is greatly appreciated.
    Thank You,
    Dana

    Edit...The tranny engages immediately when shifted to D, runs through the gears then drops into 2nd and stays there. When I stop, it shifts through the gears goes to third then drops again
    Last edited by rustyk2; 03-28-2010 at 01:10 PM.

  6. #6

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    Try unplugging the kickdown wire at the gas pedal or at the trans. Either end. If the switch is stuck it will do what yours is doing.

  7. #7
    Master Mechanic rustyk2's Avatar
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    Thanks, will try that tomorrow, getting late and raining in SC. thanks again for all the help. Could the detent switch be bad?

    Dana
    Last edited by rustyk2; 03-29-2010 at 05:02 PM.

  8. #8
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    murdog94's Avatar
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    Please keep us informed im kinda learnign as this thread progresses. Since alot of my buddies have these trannies...
    Mike

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  9. #9
    Master Mechanic rustyk2's Avatar
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    tried to unplug the wire, got it off, no change still dropping third. Any more options?

    Thank you,
    Dana

  10. #10

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    Quote Originally Posted by rustyk2 View Post
    tried to unplug the wire, got it off, no change still dropping third. Any more options?

    Thank you,
    Dana
    Are you are sure you have good manifold vacuum at the modulator? If you pull the line off the engine should speed up. If the vacuum is good and there was no oil in the vacuum line then what I would do next is look at the governor. Take the 4 bolts out and remove the cover. It's on the left rear of the transmission. These governors have a plastic gear which can wear out. Once it wears out the trans wont shift but if it's almost worn out or the gear is loose it can fall out of high gear.

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