Transmission problem

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  • Sigblitz

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    I thought about posting this in the hot rod thread, but it would be easier to manage here.

    1967 Chevy C10, turbo 400 trans. The truck sits a lot. It won't go into gear, unless you step on the gas and let the revs come down. It slips back out of gear if you give it a lot of gas.
     

    mom45

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    Forward, reverse or both? We had issues with my '84 suburban that has the TH400 not wanting to go into reverse. Turns out the tube that picks up the fluid had fallen off and was laying in the pan.
     

    PaulF

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    I thought about posting this in the hot rod thread, but it would be easier to manage here.

    1967 Chevy C10, turbo 400 trans. The truck sits a lot. It won't go into gear, unless you step on the gas and let the revs come down. It slips back out of gear if you give it a lot of gas.

    So, first a bit of a disclaimer...the transmissions I have experience with are all computer-controlled, so my diagnostic skills don't line up perfectly for your scenario, but I'm glad to maybe help rule out a couple of things.

    I would recommend a quick check of the basics. Is it leaking transmission oil? Low fluid level can result in a bevy of symptoms. There might be a dipstick to check the fluid level. Off the top of my head I think that old Chevys had to be at operating temp and in neutral to take a correct reading...could be mistaken about that though.

    I think the old mechanical automatic transmissions used vacuum to determine load/demand. My gut it telling me you might have a vacuum leak or possibly a bad diaphragm in the vacuum modulator.

    Do you have the tools or desire to dig into this yourself?

    EDIT TO ADD: I just thought about the butterfly governor...if the car doesn't get driven much you could have sticky counterweights or a gunky valve.

    Again, I am no expert with the older mechanical automatic transmissions, or with domestic transmissions in general...so I could be way off the mark, I'm just hoping to help.
     

    WebSnyper

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    I thought about posting this in the hot rod thread, but it would be easier to manage here.

    1967 Chevy C10, turbo 400 trans. The truck sits a lot. It won't go into gear, unless you step on the gas and let the revs come down. It slips back out of gear if you give it a lot of gas.


    We need some pics of the 67 C10... Love the old trucks.
     

    Sigblitz

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    Forward, reverse or both? We had issues with my '84 suburban that has the TH400 not wanting to go into reverse. Turns out the tube that picks up the fluid had fallen off and was laying in the pan.

    Yep. That goes to the reverse servo. It pushes on the band to grab the reverse clutch.
     

    Sigblitz

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    We need some pics of the 67 C10... Love the old trucks.

    It's a morning picture, so it's ugly.

    qd2cQmI.jpg
     

    Sigblitz

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    My google fu says front band is sticking. So it's enguaged?:dunno: I'm thinking the servo isn't engaging to press the band. Or the band is just stuck open, and slips more when gas is applied.
     

    Sigblitz

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    My google fu says front band is sticking. So it's enguaged?:dunno: I'm thinking the servo isn't engaging to press the band. Or the band is just stuck open, and slips more when gas is applied.

    No noises. Has fluid.

    Think I figured it's a stuck band from sitting.
     

    Sigblitz

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    I watched a video of a teardown. Customer's car sat for a while. It's a Rolls but still a T400. The valve body sprung up when he took the last bolt out, because the plastic servo was in half, leaking of course, and the spring inside the 2 halves sprung up the valve body.
     

    JCSR

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    Maybe I can run transmission fluid through it to clean it out.

    Might look into the Lucas transmission stuff. I use their power steering additive and that stuff works! My guy at NAPA said customers have had good luck with the trans additive as well.
     

    Sigblitz

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    I watched a video of a teardown. Customer's car sat for a while. It's a Rolls but still a T400. The valve body sprung up when he took the last bolt out, because the plastic servo was in half, leaking of course, and the spring inside the 2 halves sprung up the valve body.

    I think the stuck band pushed his servo in half. It couldn't press it shut, so it pressed the servo in half.

    Which goes to show, don't leave a car sit around.
     
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