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Technical Symptoms of bad stall converter?

Discussion in 'The Hokey Ass Message Board' started by wearymicrobe, Jun 3, 2016.

  1. wearymicrobe
    Joined: Jul 27, 2007
    Posts: 265

    wearymicrobe
    Member
    from San Diego

    Banging my head against the wall on this one.

    Rebuilt to stock 365 Cadillac motor, new carb, intake all gaskets, new ignition. Everything is to factory spec in terms of dwell and ignition timing. Motor will idle 100% perfectly on the stand. Runs 100% perfectly in the car outside of idle all cylinders have compression within 5% of each other, vacuum is a strong -21in/mg non fluctuating needle.

    Motor runs great in neutral ~600rpm, idle drops 150rpm like you would expect in gear and gets a seriously rough. All the usual stuff like carb spray and leak detection shows nothing. You could balance a nickel on the motor out of gear and it will not move as you throttle up. Runs great all the way up the RPM range. No amount of timing will smooth it out. Timing is correct by light and by dial gauge setting from TDC which was marked on rebuild.

    Any chance this sounds like a dying stall converter. Its one of the very few pieces that had been on the shelf for years before the build.

    This motor is in my 57 right now but will be going into a 28 roadster in about 6 months when the body is done. Pulling this and building something modern in the 57.
     
  2. How does the car react when driven?
     
  3. wearymicrobe
    Joined: Jul 27, 2007
    Posts: 265

    wearymicrobe
    Member
    from San Diego

    Other then the idle shudder drives darn near perfect. Bring the RPM up and the motor returns to being smooth as butter.
     
  4. If you don't have a dash pit that increases your idle when you put it in gear then set your idle with it in gear. If you are running enough cam to need a converter with an adjusted stall speed then it is not going to idle @ 450 RPM ( 600-150). It shouldn't idle @ 450 anyway, that will knock your lower end out quick.
     

  5. Joe H
    Joined: Feb 10, 2008
    Posts: 1,525

    Joe H
    Member

    Put a timing light on it and watch the marks as someone drops it into gear. You could have the rpm set right where the mechanical advance is just pulled in, this makes for a smooth idle. When you drop it into gear, the rpm drops enough to back off the advance causing the rough running.

    Converters usually lock up solid or free wheel, some will slip, not cause a rough running engine. When they get real tight, the car will go down the road at idle fairly easy. When they lock up, it acts just like a clutch still engaged.
     
  6. wearymicrobe
    Joined: Jul 27, 2007
    Posts: 265

    wearymicrobe
    Member
    from San Diego

    One of the first things I did, not moving at all between park/in gear.

    I have it set at 600 in gear now, running like 800 in park but not the end of the world. Definitely running smoother that way. Cam was sold as a stock unit but maybe I got something a little hotter and they just threw it in the box. Everything passed the clearance test. I would have thought I would see more of a vacuum fluctuation with a 1/4-1/2 cam if they made that mistake.
     
  7. What trans is in it?
    Are you 100% certain the vacuume modulator is working as it should ? ( if it has one)
     
  8. Now I got to ask if you have what you believe to be a stock camshaft (I never heard of a 1/4-1/2 cam only 3/4 and full race by the way) why would you run anything other then a stock converter?

    I am not sure but if it is a stock transmission it may actually have a tauros (sp).
     
  9. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    Do as Beaner said, set the idle speed in gear, don't worry that it's above 800 in Park. Also, spend some quality time setting the idle air/fuel adjustment. Assuming this is a dual or quad, make your adjustment on 1 side, then do the other, then go back and do the first side again, then go back and do the second side one more time. Adjust the screw to achieve the highest idle speed, then re-set the idle speed, then roll the screw in until you see 20 rpm drop in idle speed, then adjust the idle speed back up. Do this for both sides, always starting with the idle speed and returning to the idle speed in between each adjustment. This can make a big difference in the smoothness of the idle in gear.
     
  10. wearymicrobe
    Joined: Jul 27, 2007
    Posts: 265

    wearymicrobe
    Member
    from San Diego


    I will give that a try. I normally just set them using a vacuum gauge.
     
  11. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    I've found the tachometer more responsive than a vacuum gauge.
     
  12. flamedabone
    Joined: Aug 3, 2001
    Posts: 5,440

    flamedabone
    ALLIANCE MEMBER

    Go buy a good dial back timing light and record the following numbers:

    At idle in park with vac advance hose removed from pot and plugged
    At 3500 rpms vac plugged
    At idle in park with vac hooked up.
    At 3500 vac hooked up.
    At idle in gear with and without vac plugged.

    The numbers for these variables will answer your question, I promise.

    -Abone.
     
  13. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 9,214

    mgtstumpy
    Member

    A friend had a Buick with similar issues and it turned out to be something simple like a blocked transmission vent pipe?
     
  14. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 6,695

    56sedandelivery
    Member Emeritus

    If you've got a converter going away, the transmission fluid going to look like a metallic paint job.
    I am Butch/56sedandelivery.
     
    falcongeorge likes this.
  15. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,213

    sunbeam
    Member

    Motors manual calls for Idle speed of 420 in drive on a stock engine.
     
  16. wearymicrobe
    Joined: Jul 27, 2007
    Posts: 265

    wearymicrobe
    Member
    from San Diego

    Replying to my own thread I am a moron. Check your tools. tach readout on my timing gun was off by 1000rpm as I was checking timing up high and 100+ at idle. New timing gun and using one of my optical tach readers idle is set at 550 and not wavering in the slightest. Any lower then that and it has some small power off idle issues. Vacuum is clean and steady and running great. Don't be a moron like me double check everything and calibrate your tools
     

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