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Technical Abother SBC shift issue

Discussion in 'The Hokey Ass Message Board' started by Daniel Boyce, Jun 29, 2021.

  1. Daniel Boyce
    Joined: Jan 8, 2016
    Posts: 5

    Daniel Boyce

    I'm seeking advice from the congregation.

    I have stock, very mild cammed 350/400 combo in a friends truck that I’m working on and I can’t seem to find a culprit to my issue. My issue is that when I shift from park to any drive gear it revs up slightly, slams into gear and stalls. I have to work the brake and skinny to keep it going and when I mange to get it in gear without stalling it feels like it has a lot of load on it as well.

    I couldn’t find any vacuum leaks, and everything seems to be getting vacuum from the proper location. The engines makes 18hg. The converter feels stock-ish and is to the owners knowledge. The trans fluid is fresh and so is the carb. The engine runs good otherwise. I'm leaning toward the converter but have never experienced this before and wanted to double check with you guys before I drop the trans.

    Thoughts?
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 49,339

    squirrel
    Member

    What is the idle speed? and does it really change, when you move the shift lever? If so, that indicates it might not have any free play in the throttle linkage, which could be the problem.
     
  3. Daniel Boyce
    Joined: Jan 8, 2016
    Posts: 5

    Daniel Boyce

    Idle speed is about 750 in park and 850 in gear. The throttle linkage has enough slack for that not to be an issue.
     
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 49,339

    squirrel
    Member

    Well, something funky is going on if it changes when you move the lever out of Park. Figure out what it is that's happening.
     

  5. squirrel
    Joined: Sep 23, 2004
    Posts: 49,339

    squirrel
    Member

    What type of carburetor does it have?
     
  6. Daniel Boyce
    Joined: Jan 8, 2016
    Posts: 5

    Daniel Boyce

    It has a new edelbrock 600 with vacuum secondaries.
     
  7. greybeard360
    Joined: Feb 28, 2008
    Posts: 1,750

    greybeard360
    Member

    Have you tried driving it?
     
  8. Daniel Boyce
    Joined: Jan 8, 2016
    Posts: 5

    Daniel Boyce

    I have a few miles on it and it shifts firm and where I'd like it to.
     
  9. Sounds backword. Is there an AC idle solenoid causing the issue?
     
  10. Daniel Boyce
    Joined: Jan 8, 2016
    Posts: 5

    Daniel Boyce

    The truck doesn't have AC.
     
  11. squirrel
    Joined: Sep 23, 2004
    Posts: 49,339

    squirrel
    Member

    If you can't find anything in the throttle linkage that's causing the problem, then I don't know what it could be....

    The idle speed is kind of high for a stock converter, which is why it clunks.
     
  12. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 3,401

    2OLD2FAST
    Member
    from illinois

    Why would the no load speed be higher than the loaded speed ?
    Try disconnecting the vacuum advance , reset the idle & test...
     
  13. TA DAD
    Joined: Mar 2, 2014
    Posts: 435

    TA DAD
    Member
    from NC

    this is like another " my flywheel won't line up "
     
    ottoman and squirrel like this.
  14. With a non-OEM carburetor especially, you'll want to make sure that the return spring is sufficient to close the throttle at idle. Also make sure the throttle cable/linkage isn't routed in such a way that it's putting itself in a bind. TH400 trans uses a switch for the kick-down, doesn't it?
     
  15. jimmy six
    Joined: Mar 21, 2006
    Posts: 9,508

    jimmy six
    ALLIANCE MEMBER

    I’ve never seen a SBC shift.
     
    ottoman likes this.
  16. squirrel
    Joined: Sep 23, 2004
    Posts: 49,339

    squirrel
    Member

    Yes, it does.
     
  17. Pete Eastwood
    Joined: Jul 27, 2011
    Posts: 1,020

    Pete Eastwood
    Member
    from california

    I'd really double check the throttle linkage .
    Watch what happens when you drop it in gear .
    I've seen it be a problem , especially with cable throttle linkage !
     
  18. Hollywood-East
    Joined: Mar 13, 2008
    Posts: 1,469

    Hollywood-East
    Member

    It's called LS, part of the alphabet group LGB..etc.
     
    jimmy six likes this.
  19. DDDenny
    Joined: Feb 6, 2015
    Posts: 15,091

    DDDenny
    Member
    from oregon

    I've seen plenty of sbc "core shift" Jimmy!
     
    ottoman likes this.
  20. jimmy six
    Joined: Mar 21, 2006
    Posts: 9,508

    jimmy six
    ALLIANCE MEMBER

    That doesn’t count…:rolleyes:
     
  21. jimmy six
    Joined: Mar 21, 2006
    Posts: 9,508

    jimmy six
    ALLIANCE MEMBER

    LS = Y-block.
     
    Hollywood-East and 30tudor like this.
  22. Budget36
    Joined: Nov 29, 2014
    Posts: 6,792

    Budget36
    Member

    How about a pic of the carburetor and what’s hooked to it? Could a bad/loose motor mount be clocking the engine over and pulling some on the throttle?
     

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