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th400 question

Discussion in 'The Garage' started by Jonny-K5, Aug 24, 2005.

  1. Jonny-K5

    Jonny-K5 1/2 ton status

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    i just swapped out the original th400 in my 65' pickup with another th400 out of a 79 pickup. everything bolted up fine, but now i cant manually shift under load, i have to let off the gas to move the column shift lever. is there something internal that could be causing this? or is linkage the only possibility. its got me scratching my head causs the old tranny worked fine. the 79' th400 worked fine as well before being pulled.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    But it's ok if you put it in drive and head out? Shifts gears ok and what not?

    Only thing that controls manual shifting is the shift assembly, under load only reason I can think of a difference would be the transmission torquing to one side under load messing with the linkage. Seems unlikely, but everything internal that deals with manual shifting shouldn't care whether the tranny is under load or not.
     
  3. Jonny-K5

    Jonny-K5 1/2 ton status

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    ya, shifts fine if you leave it in drive. besides the fact that it shifts around 3000rpm at full throttle.

    torque twisting the linkage is all i could think of too. but i dont know why it would only affect this tranny. i did replace the tranny mount, the old one was split in two. seems like that would make things better, not worse.

    i plan to put a floor shifter on it eventually. hopefully that will eliminate the problem
     
  4. HarryH3

    HarryH3 1 ton status Author

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    Check your motor mounts also. If the tranny mount was broken, it could be because the engine is moving around too much.
     
  5. asisco72

    asisco72 Registered Member

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    did you hook you vacum line back to the diphram looking thing on top of the trans
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    Modulator affects how firm the tranny shifts, and a bit towards WHEN it shifts, but even unhooked it isn't going to physically prevent the manual shifting of the trans.
     
  7. Jonny-K5

    Jonny-K5 1/2 ton status

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    mounts are new and i have a safety chain hooked to the motor so if it does break, it isnt moving much.
     

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