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48 Champion: "Downshift" Issue

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  • Transmission / Overdrive: 48 Champion: "Downshift" Issue

    During my last couple of drives (each 20-30 miles, 40-60 minutes, average speed 30-45mph) maybe 2-3 times on each trip my car momentarily lurches like it wants to downshift on its own. Some details:
    • It’s never done this before in my 6 years (3,000+ miles) of owning/driving it
    • 3 speed w/overdrive (overdrive has worked for the last 3 years. It did not work when I acquired the car but a new kickdown switch fixed it and it’s worked great ever since)
    • Engine and transmission are original and not modified in any way
    • Just under 64,000 original miles
    • All transmission, OD and diff. gear oil flushed and replaced by me when I got the car
    The “downshifts” are random. They have happened at different speeds (5 to 45mph) and occur upon first hitting the road and/or after driving for 45 minutes.
    There is no gear grinding when it happens (or afterwards), and besides this issue, the car runs great and at a constant 175oF unless in traffic but even then, no overheating.

    When it happens, however, it's not really downshifting as I can continue driving normally without the engine revving. No upshifting is necessary, the car just momentary “jerks” as if I actually did downshift.

    Any help, advice, or tips to help me understand what is happening and hopefully head off any serious problems is greatly appreciated!

  • #2
    My guess would be that maybe the wire from the kickdown switch to the coil is chafing against something, and grounding out the ignition intermittently.
    Gord Richmond, within Weasel range of the Alberta Badlands

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    • #3
      Thanks - I just checked and all wires seem to be secure and in place. Some of the terminals were exposing a bit of wire but did not seem to be touching anything.

      I did, however, notice that the speedo cable was resting against the side of the kickdown switch. I never noticed that before when I replaced the switch. Could that be the cause? Is there a proper way to secure it out of the way? Perhaps to the firewall...but I don't see any obvious holes for a clamp to attach to it?

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      • #4
        For a guess, the kickdown switch or an exposed wire is grounding through the speedometer cable. It may not be touching all the time, just when some vibration brings the two parts together at speed..

        Years ago, the parking brake cable on my '47 Champion was grounding something so I put a piece of rubber tubing over it.
        Bill Jarvis

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        • #5
          Greenstude - thanks for your response. I will try that on the speedo cable and report back! It does not rest on the switch but is close enough where it could certainly bump/touch it when driving. Hopefully it is just something simple like that...

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          • #6
            make double sure that your OD cable (manual) is fully bottoming on the back land of the OD when pushed in....

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            • #7
              does this happen in overdrive only or in direct drive too? Are there any unusual sounds at the same time?

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              • #8
                I will have a chance later today to check the position of the OD cable

                mapman - I believe it is only happening in OD. It most always happens at "higher" speeds (35-50) but it has also happened on occasion as I am slowing down to 10-15, but I seem to be freewheeling at that point vs. direct drive. ...and no unusual sounds at all; just the "jolt" of feeling like a downshift, then I continue to drive normally

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                • #9
                  With the hand brake applied, wheels chocked, engine at idle speed, start wiggle testing all the overdrive wires. Wires around relay, kickdown switch, distributor, and on down to the transmission. See if you can induce a stumble or lurch.
                  So.....if I'm 'pre-approved' why do you want me to fill out an application?

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                  • #10
                    I would suggest a process of elimination, firstly disconnect the OD kick down wire from the coil and drive it that way for a while. It won't kick down from OD with that wire removed, this is just a process of elimination. See if it stumbles. You will have to come to a stop to pull the cable for conventional drive.

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                    • #11
                      Thanks for the additional suggestions! I will have a chance to try both this weekend and report back...

                      ...I did check the OD cable today and it looks to be functioning properly - it is fully bottoming on the back land of the OD when pushed in

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                      • #12
                        I have read the problem and suggestions to address it. If someone has discussed the mechanical relationship between the kick-down switch and how it mounts to the "kick-down switch bracket"...I must have missed it. So, I grabbed my trusty iPhone with its built-in camera and went to my cave to take a couple of pics of the linkage on my '48 Business Coupe. What you may be experiencing is a problem with your kick-down switch being adjusted just a tad too far in toward the "paddle" contact of the linkage. I will post two pictures. One will show the linkage contact mechanism at rest (idle) and the other much closer as when you are underway with the accelerator pedal pushed in maintaining traffic speed.

                        The trick to preventing inadvertent kick-down is to adjust the switch so that the accelerator must be at maximum (floorboard) to activate the kick-down when chugging up a steep hill or passing a slower car. It is a very sensitive adjustment and there is very little movement one way or another to find the "sweet spot" to get the switch just right. When the switch is screwed into that bracket too far, it does not take much of a bounce of the foot while driving down the road to cause an unwanted kick-down. I know, I spent a whole afternoon one day monkeying with the one on my truck. I kept moving the switch too much when making adjustments. That's when I realized that it only takes a tiny movement (in or out) to get it right. If I'm successful with the pics, the two will be below. Hope this helps.
                        Click image for larger version

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                        Click image for larger version

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                        John Clary
                        Greer, SC

                        SDC member since 1975

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                        • #13
                          Thanks jclary for the additional tip and clear photos! I remember when I installed the new kickdown switch how touchy it was to adjust; perhaps I was a bit off or it has changed it's position slightly over time. I will take a look at that as well, and hope to report back a successful solution this weekend.

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                          • #14
                            jclary, now you have me thinking...how far in does the kickdown switch actually have to go to engage?

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                            • #15
                              Originally posted by pjkush View Post
                              jclary, now you have me thinking...how far in does the kickdown switch actually have to go to engage?
                              Honestly...I don't know. You could take a multimeter, set it for continuity, and test it (static) to see how much the plunger moves to activate it. But, that is only one part of the equation. That switch just de-activates and moves the circuit to the two other wires to provide the "momentary" circuit break so the overdrive solenoid can disengage. Besides the switch itself, there is the condition of the accelerator linkage and the travel of the contact (paddle) for the switch plunger. That's the reason for the long threaded snout on the switch and the jam nuts to lock it into place. I suppose, if you run out of adjustment length, your next step would be to bend the paddle. Bending the paddle on the linkage would be my last resort.
                              John Clary
                              Greer, SC

                              SDC member since 1975

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