Ideal Shift points for 904

Transmission and Drivetrain Tech

  1. C2ndLTpigeon

    C2ndLTpigeon Mopar or no Car! FABO Gold Member

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    Hello,

    I wanted to see if anyone might know what the target speed should be for 1-2 and 2-3 shifts in a 904 transmission? Im talking about a gradual up to speed transition and not WOT launches.
    Mine will shift relatively close and pretty much be in 3rd gear at around 20 MPH.
    Shift transition has been happening sooner since I swapped from 2.76 gears to 3.55's.
    My 904 has less than 1000 miles on the rebuild and it also has a B&M shift kit installed.
    Might need to adjust my kickdown.
    Any help would be appreciated.
     
  2. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    Kinda late tonight for this old man, but I don't think you are making sense. What engine/ what tires (diameter) and rear gear? ?Engine RPM?
     
  3. 70aarcuda

    70aarcuda Master Hoader of SBM FABO Gold Member

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    this is what google said...and they are never wrong...

    On level ground with moderate acceleration, the 904 typically shifted 1-2 at about 12-16 mph and 2-3 at about 23-25 mph. Full throttle, 1-2 could be as late as 35-40 mph and 2-3 as late as 65-70 mph
     
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    • C2ndLTpigeon

      C2ndLTpigeon Mopar or no Car! FABO Gold Member

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      Ok ill make it a little more simpler, before I swapped rear ends I had a 7 1/4 with 2.76 gears Stock Steel 15 inch rims. 1-2 used to shift about 15 mph and it would be in 3rd gear at 25-30 mph on smooth acceleration.

      Now I swapped a 8 1/4 with 3.55 gears, same rims and 1-2 shift is at about 10 mph and in 3rd gear at or before 15 mph under smooth accel.
      I will get RPM shift speeds tomorrow. Ive been going off the speedo.
      Would the now taller gear ratio be the cause since RPMs are higher with the new ratio?
      Would an adjustment of the kickdown be needed after changing gears?
       
    • C2ndLTpigeon

      C2ndLTpigeon Mopar or no Car! FABO Gold Member

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      So possibly a throttle pressure/Kickdown adjustment to make shifts later
       
    • DFX 340 Duster

      DFX 340 Duster FABO Gold Member FABO Gold Member

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      Did you change the speedometer gear to the right number of teeth for the gear ratio and tire?
       
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      • C2ndLTpigeon

        C2ndLTpigeon Mopar or no Car! FABO Gold Member

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        Yes I did, has the correct one in there, Red 36 teeth, verified speed is correct by GPS.
         
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        • CudaFactHackJob

          CudaFactHackJob FABO Gold Member FABO Gold Member

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          Higher rpms? yes....readjust kickdown? of course not. KD has one setting. Linkage might be mismatched.
           
        • AJ/FormS

          AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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          Automatic upshifts are a highly personal affair.
          But IMO, into third by 20, is too soon for all but grandpa-style driving.
          Your choices for correction, if the linkages are right, are;
          Less governor pressure /(a lighter fly-weight) or more throttle pressure/(KD adjustment) to suppress the shift.
          Sooner or later, you will run out of KD adjustment and the carb will no longer go to WOT. At this point you will HAVE to go to the governor, or to reduce the Line-pressure ... which usually is not a good thing to do. In any case, adjusting the governor is easier.
          You can tie back the TP lever at the trans, in such a way as to set the minimum upshift pressure, but you have to do it in such a way that still allows the linkage to push the lever all the way to the rear.

          If you have a factory KD linkage, then you will see a long slot for the carbstud to rotate thru. This allows a lot of throttle opening before anything even happens at the trans. In this case your only option is to change the governor.
           
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          • C2ndLTpigeon

            C2ndLTpigeon Mopar or no Car! FABO Gold Member

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            That's a good description of gradual acceleration, grandpa driving. But yes I agree it does not feel like it should be in 3rd at 20 MPH

            Ok, so before I did any work to my engine and trans I did not have this issue when the teener was a 2 bbl stock. Once I went to 4 bbl and had to find a kickdown lever for a four barrel as you will see in the pictures this is my current set up. I purchased the kickdown rod from Johnny Dart on here and its the same setup he is using on his and works great.
            It is a non adjustable rod at the carb so the only way I can adjust it is with the 2nd rod linkage connecting to the bell crank.

            Im hoping its as simple as an adjustment.

            137652396_398486354555623_3119551334122178969_n.jpg 138062658_399804064441284_292261656228905408_n.jpg 137672718_1467288536950845_2932602154589325898_n.jpg
             
          • C2ndLTpigeon

            C2ndLTpigeon Mopar or no Car! FABO Gold Member

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            I will check, from what I read the throttle should be WOT and the KD lever all the way back?
             
          • AJ/FormS

            AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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            yes.

            But as you can imagine, the KD mechanism, only delays the upshifts when it is actively adjusting the pressure inside the trans.
            To see what I mean; flip the green return spring off the KD link, then gently push the rod to the back until you feel resistance, then hold it there. Next open the throttle until it stops at the back of the slot. When it does, this is now at the throttle opening required for the KD link to begin doing something .
            Obviously, at lesser throttle openings the KD mech is NOT DOING ANYTHING at all.
            So , in this dead-zone, is where the governor is commanding the shifts. If you want the trans to behave differently in that zone, then you will have to make changes to it; as detailed in my earlier post.
             
            Last edited: Jan 10, 2021
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            • C2ndLTpigeon

              C2ndLTpigeon Mopar or no Car! FABO Gold Member

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              I will mess with this after work and post my findings.
               
            • C2ndLTpigeon

              C2ndLTpigeon Mopar or no Car! FABO Gold Member

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              From what I can tell based on what you said, is with the spring off and holding it at the first sign of resistance my throttle plates are about half way open.

              From time to time when I WOT the car hit will have delayed shifts which feels about right, but obviously we don't always WOT green lights (unless you want a ticket)
              So this is where (grandpa driving comes in) Just wanted to make sure the transmission is operating correctly. I don't want to run the risk of smoking the transmission I just rebuilt.
               
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              • AJ/FormS

                AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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                If you have synced the Throttle WOT to the WOT KD position. then your trans will be fine.
                The delayed upshifts speak to the Line-Pressure having been increased.
                If you don't like the grandpa PT upshifts (too early), you can only change that by modding the governor. Which really is not overly complicated. The thing that will take the longest is just getting the back of the car up high enough to scoot under it,lol.
                 
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                • C2ndLTpigeon

                  C2ndLTpigeon Mopar or no Car! FABO Gold Member

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                  I will double check this later on.

                  Once again I appreciate all your help.
                  Lots of things to learn making the switch from 4 cylinder cars to real cars!
                   
                • toolmanmike

                  toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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                  You need to adjust your kickdown in my opinion. I always set mine a little tight. The shifts are higher and firmer. In all the years of Mopars I have only had 1 Torqueflite fail and the link between the servo and the reverse ban fell out because the band needed adjustment. I lost reverse and found the link in the bottom of the pan. After I replaced the transmission of course. I was working at the speed shop and B&M Torqueflites were pretty cheap back then.
                   
                • C2ndLTpigeon

                  C2ndLTpigeon Mopar or no Car! FABO Gold Member

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                  Could you explain what you mean by a little tight? Is this bringing the KD rod towards the front of the engine more?
                   
                • toolmanmike

                  toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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                  Yes. Let me see if I can find a photo.
                   
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                  • toolmanmike

                    toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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                    There should be no gap between the back of the slot and the pin. I start there and adjust the slot towards the front a turn or two at a time until it feels right.

                    kickdown.JPG
                     
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                    • C2ndLTpigeon

                      C2ndLTpigeon Mopar or no Car! FABO Gold Member

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                      And since mine is a fixed rod at the carburetor and not threaded like yours will doing this at the middle rod like I showed above achieve the same result?
                       
                    • toolmanmike

                      toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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                      Yes it should. I would lengthen it to make it shift a bit higher.
                       
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                      • CudaFactHackJob

                        CudaFactHackJob FABO Gold Member FABO Gold Member

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                        Don't use the gas pedal to set it unless you know it is actually opening the carb all the way WOT.
                         
                      • C2ndLTpigeon

                        C2ndLTpigeon Mopar or no Car! FABO Gold Member

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                        Ok so while I am trying to get WOT set, I have it at the max the gas pedal will allow but the plates could open just a tad more. I cant adjust the cable any more since this will not let it return to idle. Any suggestions to getting the throttle pedal to open that last bit of throttle?
                         
                      • CudaFactHackJob

                        CudaFactHackJob FABO Gold Member FABO Gold Member

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                        Disconnect the gas pedal to set it, then hook it back up..
                         
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