I Give Up - Why an A-904 Rolls A Sprag?

Transmission and Drivetrain Tech

  1. doc540

    doc540 Well-Known Member

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    My local shop (with decades of MoPar rebuilding experience) gave me most of my money back today. They can't fix my transmission.

    The A-904 in my '61 Lancer has rolled the sprag TWICE.

    The second time it rolled the sprag of an AandA Transmission bolt-in sprag kit. http://www.http://www.aandatrans.com/Default.aspx.com

    The Slant 6 isn't making more than 200hp, I haven't raced it, I'm not doing burnouts or driving it hard.

    It has simply shifted from First to Reverse when in Drive.


    Why?:banghead:
     
  2. TrailBeast

    TrailBeast AKA Mopars4us on Youtube

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    Just off the top it seems like it would almost have to be a linkage issue.

    Do you mean for no apparent reason it shifts down into low all by itself?
    And that this is why the sprag is rolling over?
     
  3. doc540

    doc540 Well-Known Member

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    Thanks for offering help.

    The '61 A-904 is cable operated from the pushbuttons (no external linkage on the trans).

    When in "D" and taking off (slowly) from a stop, instead of shifting from "1" to "2", is shifts back down into REVERSE and rolls the sprag.

    Same result as if one was driving 20+mph and manually shifting to reverse. It frags it. :pale:
     
  4. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    What has been changed? I can barely spell "Torqueflite" but sounds like a VB, bad, leak, drilled, ??
     
  5. doc540

    doc540 Well-Known Member

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    Just the normal rebuild - clutches, etc.
     
  6. Mopar Tim

    Mopar Tim FABO Gold Member FABO Gold Member

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    VB issue. Doing that will sure blow the sprang.
     
  7. doc540

    doc540 Well-Known Member

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    That's something we haven't changed.

    I can get another one from AandA for $200 with a core exchange.
     
  8. RustyRatRod

    RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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    Get another valve body.
     
  9. doc540

    doc540 Well-Known Member

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    Thanks for the help.

    I got one lined up.
     
  10. doc540

    doc540 Well-Known Member

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    Another local shop is going to rebuild it.

    They seem knowledgeable and have A-904 parts in stock including a valve body. They also do machine work and repair.

    Thanks for all the info and putting up with my whining. :eek:
     
  11. TrailBeast

    TrailBeast AKA Mopars4us on Youtube

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    I did that once a long time ago at 60, but it didn't roll the sprag.
    The crankshaft reversed direction instantly but the cam didn't. :D

    It looks like you got the advice you needed.
    I asked what I did to clarify what the symptoms were, and it HAS to be the valve body (OR possibly sealing rings left out on the rebuild) 2nd gear oil circuit crossing over to the reverse band servo somehow with the drivetrain still trying to drive the other direction, but I sure can't see how that could happen.
    Also the more I think about it the more I have a hard time believing a valve body could do that at all with no driver input.

    Air checking is the way to go, but I also understand that it's hard to tell someone that supposedly knows what they are doing how to do it. :D

    BTW, a cable is still a linkage that can move causing problems. :D
     
  12. FredS

    FredS Well-Known Member

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    does the current valve body have a shift kit supplied manual valve in it? Easy to spot if you're looking at the valve body. If it does, and they didn't file the vb top piece end land for this manual valve, it'll vent 3rd into the reverse port and either fry reverse or nail the sprag.
     
  13. doc540

    doc540 Well-Known Member

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    Thanks again, gents.

    FredS, I'll print your comment and make sure the rebuilder takes note.
     
  14. TrailBeast

    TrailBeast AKA Mopars4us on Youtube

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    But that would be on the 2-3 shift and I understood it does it on the 1-2.

    That's a dang good call though if that's what it does Fred.
     
  15. nm9stheham

    nm9stheham Well-Known Member

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    I had similar issues with a C4 once..... it was not engaging the right items and trans was doing the wrong thing (with no damage fortunately). Turned out the be the VB gasket to the case.
     
  16. AJ/FormS

    AJ/FormS 68 Formua-S fastback clone 367/A833/GVod/3.55s FABO Gold Member

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    I studied the stock hydraulic circuits for a good long while, and could not see it happening with stock parts, unless something in the VB was busted, allowing a pressure crossover. Even then,that circuit is dumped straight into the pan, in every manual valve position except reverse. And at such a low rpm, the throttle pressure is very low, and at almost zero driveshaft rpm there will be little to no governor pressure. I would have thought that not enough line pressure could leak into the reverse circuit, to cause this situation.
    Hydraulically I couldn't see it.
     
  17. AJ/FormS

    AJ/FormS 68 Formua-S fastback clone 367/A833/GVod/3.55s FABO Gold Member

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    nm9
    I had a situation with a C-4 once too. As to automatics, I normally stick to Mopars and old TH350/400s (cuz they're easy),but many years ago my broke neighbor talked me into rebuilding the tired old tranny in his Ford Ltd.
    Well, when I was done it worked great; except there was no engine-braking in Drive.Take your foot of the gas and it might as well have been in Neutral. After RnR-ing the tranny again and the VB separately,as well, and spending a lot of time head-scratching, I came to the conclusion that I had no clue what to do. I did what I believed was the right thing to do. I gave him all his labor money back. He drove that car,in that condition, as a DD for many years, until the engine was really,really,really tired.He replaced it with a Plymouth.
    I told myself no C4s ever again.
     
  18. doc540

    doc540 Well-Known Member

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    I appreciate the discussion.

    Monday it goes back on the lift at another shop.

    If they find anything, I'll report it here.
     
  19. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    I know little of these. Some pinhole, etc, in the VB? Leaking across channels under the cover plate, etc?
     
  20. doc540

    doc540 Well-Known Member

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    2nd shop is now on its second rebuild.

    We've learned that all front planet gears are not the same.

    They changed after 1961, and we've been using the wrong ones.

    Cross your fingers that the third time's a charm.
     
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