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Help Needed!!

Discussion in '1982-Present GM Diesel' started by TK5, Mar 6, 2003.

  1. TK5

    TK5 1/2 ton status

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    /forums/images/graemlins/confused.gifI had a busted piston skirt and replaced it and rings. Everything is running Fine, but I have a new problem. Now the transmission (TH-350) won't shift after everything is back together. I've checked the vacuum pressure from the pump (idling 5-15 psi), (with the motor accelerated (30-75 psi). I am told it should be stationary all the way round, idling and accelerating? Is this true? Could I a vacuum pump going bad? I have checked all vacuum lines and hoses and they are fine.

    Any help is really appreciated. I'm getting tired of driving my Granny Van (6.2 GMC 2500) around. It's starting to crack my style plus it has been in the 60's this week and would love to drop the rag top.

    Thanks in Advance. /forums/images/graemlins/k5.gif
     
  2. TK5

    TK5 1/2 ton status

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    WEll the tranny is shifting, but not quite the way it sshould I by-passed the vacuum module that the vacuum pump runs to and runs to the transmission. So I'm guessing the vacuum module is bad. I checked the vacuum from the module to the tranny and it was 0-5 at idle and at accelerated throttle there was no vacuum.
     
  3. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    The vac module controls the upshift, but I'm not exactly sure how that would work on a diesel. On a gas engine isn't the vac module connected to manifold vacuum? Less vacuum equals more throttle and the tranny would shift later. The diesel uses a vacuum pump and a vacuum resevoir right?

    Rene
     
  4. TK5

    TK5 1/2 ton status

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    That's how it works. I'm no diesel expert, just trying to apply gasser mentality tro the diesel. The diesel has the vacuum pump but there is not a reservoir for vacuum.. I know that it is not shifting like it was before I replaced the piston and rings, but it is shifting, further along than I was yesterday.

    I was hoping some diesel guru here could shed a little light on my situation. /forums/images/graemlins/k5.gif
     
  5. bigblock454

    bigblock454 Clack Clack Clack Premium Member

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    In a gasser the transmition is connected directly to manifold vacuum. The lower the vacuum the higher the shift point. If you disconnected the vacuum line the trans would shift at max possible RPM.

    Since diesels don't make manifold vacuum they use a vacuum pump and a Vacuuum Regulator Valve. This valve is connected directly to the injection pump and is perportional to the throttle position. The higher the throttle the lower the vacuum. This basically copies the gasser function.
     
  6. TK5

    TK5 1/2 ton status

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    Thanks, that is what I was thinking. I read too much, but that is basicly what I have read. You just said it in a more clear method than the book or the net.

    I also came to a conclusion that I may have reversed the vacuum lines. I will check it out tomorrow.

    Thanks again.
     

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