727 Not down shifting. :(

Engine, Transmission & Driveline

  1. WOT440

    WOT440 Member

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    As title states, transmission not down shifting when coming to a stop (always). I say always as sometimes, I feel it downshift. The last test run, it up shifted fine. Normal hard shift from 1st to 2nd and from 2nd to drive. Kick down works as it should. Throttle and kickdown linkage adjusted to FSM. My issue is when I slowed down to turn into my drive, which is an upward incline, the transmission felt like it was still in drive, and never shifted down to accommodate for the incline. Any thoughts would be appreciated. TIA. I should add...this is a rebuilt 727 from Advance Auto, with less than 200 miles, installed by the PO. Also should add the linkage geometry is slightly off from stock, due to Edelbrock performer intake.
     
    Last edited: Oct 17, 2021
  2. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    What year?

    Later cars have a part throttle down shift module that can be added to earlier cars if needed. Both my cars have been changed to this and it’s a great mod.
     
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  3. cbarge

    cbarge World Famous Barge in a Budget FCBO Gold Member

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    John IIRC he has a 68 300. So possibly no PTKD.
     
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  4. CBODY67

    CBODY67 Old Man with a Hat

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    This would be a valve body issue rather than a throttle linkage adjustment issue. Possibly a shuttle valve spring has broken which does not let the valve move in the valve body as it shiould, resulting in no speed-related downshift when slowing to a stop. Or a sticking shuttle valve itself? Might get them to check the governor weights, too, for unrestricted operation?

    The shuttle valves in the valve body operate on a pressure vs spring principle. As the governor pressure builds, it compresses the spring to move the valve to put fliuid in another circuit, then cycle repeat until it is in direct gear (i.e., 3rd gear in "D"). Then the process reverses when the speed drops, unless the throttle is moved past the kickdown/downshift point in relation to road speed.

    Take it back to them quickly! To ensure any existing warranty might still be in effect!

    Please keep us posted on how things come out.

    CBODY67
     
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  5. WOT440

    WOT440 Member

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    Sorry it's a 68' Chrysler. I'll look into the part throttle down shift module mod.
     
    Last edited: Oct 17, 2021
  6. WOT440

    WOT440 Member

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    Thank you for the explanation. I read that if the governor pressure to high it could result in downshift problems. What I don't understand is why it will down shift with no problems when I manually shift.
     
    Last edited: Oct 17, 2021
  7. my5thmopar

    my5thmopar Member

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    I had the exact same issue with a 904 I rebuilt. It was a bad governor valve. Cleaning didn’t fix it and the shuttle moved freely. I had to replace it. As already mentioned, take it back but, the warranty is probably for the PO. It’s pretty easy to get the tail shaft off. I don’t remember exactly but, there’s a snap ring to be removed. Craig
     
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  8. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    Thinking about this, and looking at the FSM, the trans should downshift to first if you get under 10 MPH.

    So, maybe the thing to do is look at the entry speed into your driveway first so you can figure that part out. Maybe even try stopping first. Not saying that's correct, just thinking out loud to help with diagnosing.

    So, also looking at the FSM, the easy things to check would be the linkage... Since the geometry has been changed, that makes the linkage first on the list. I recently saw an Uncle Tony video about the linkage. Might be worth a watch.



    From there... I'm just knowledgeable to get into trouble with transmissions so a look at the FSM gives some better suggestions.
     
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  9. CBODY67

    CBODY67 Old Man with a Hat

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    When you manually downshift, you're moving the valves manually rather than let governor pressure move them against spring pressure. Additionally. manual "1" is not the same as "D" when coming to a stop or taking off--different sections involved.
     
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  10. WOT440

    WOT440 Member

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    Last edited: Nov 1, 2021