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Very sluggish shift from second to third while accelerating - 1961 Lark V8 Automatic

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  • Transmission / Overdrive: Very sluggish shift from second to third while accelerating - 1961 Lark V8 Automatic

    My 1961 Lark wagon just developed an annoying habit over the past few days. While hopping on the freeway and accelerating, I've noticed that the shift into third is occurring more around 40-50mph in some cases, typically when I'm applying a lot of gas on the on-ramp. In general, that sluggish shift only happens once or twice on a highway drive of 10-12 miles (my morning commute) as I have noticed since the problem developed about a week or two ago. I think it is doing the same even in slower cases of accelerating (street driving) where the shift into third feels like its happening around 35-40mph as opposed to 30-35, but it's much less noticeable in those cases.

    History of the car: The engine and transmission were rebuilt around 3500 miles ago, or 3 years ago. They are original to the car - a 259 V-8 and a three-speed automatic transmission (I have to check the fluids when it is in Drive, so I believe it's a Flight-o-matic). I am now really starting to break it in having the opportunity to take it on a few longer highway trips from San Diego to LA, or out the high desert as well as using it on my 2x a week commute from SD to La Jolla. Work done on the car: installation of a 4bbl Edelbrock carburetor around 1800-2000 miles ago and a few months of follow-up tuning of the carb. Front and rear suspension rebuilt (1500 miles ago). Motor mounts and transmission mounts are new. Problems noticed that are possibly related: Prior to installation of the new transmission mount, the car would not really go into park. That's been fixed. However, sometimes it's hard to distinguish between being in Drive and Low - I mean I know when I'm in Low and I know when I'm in Drive while driving, but in the act of shifting I only need to give a slight push of the selector either up or down in order to switch from between D and L - as opposed to the more noticeably physical act of transitioning (pulling back the selector and feeling slight resistance) from N to D or L to R.

    Reading through the shop manual, I am suspecting that this a linkage related issue, and may even have something to do with how the carburetor is linked to the transmission but would really love to hear the opinions of more knowledgeable persons!


    - - - Updated - - -

    Also, are there mechanics in the San Diego area tied to the club who may be able to help out with this?

  • #2
    Can you force an upshift by lifting your foot off the accelerator, at say, 30 mph?
    Gord Richmond, within Weasel range of the Alberta Badlands


    • #3
      I'll try that! I'm going on a small trip tomorrow on the freeway to visit the alignment shop (rear tires needed rebalancing). If that works, I'll note it on the thread!

      Just to be clear, though, if I'm entering the onramp at 20-25mph and not taking my foot off the accelerator until hitting 50-55 in order to enter the slow lane, should I expect such a sluggish reaction? Should I normally have to take my foot off the pedal at around 30-35mph in order for the shift to occur at the proper speed? Thanks!


      • #4
        No, normally you don't have to lift your throttle foot for it to make an upshift, unless you really have your foot in it. I would expect closed-throttle upshift to occur at 20-30 mph, and full-throttle upshift at 60-70 mph. It sounds like your throttle valve linkage may need adjustment. Collapsed transmission mounts often manifest as shift timing problems. Please note that the transmission throttle valve is not simply a "kick-down" linkage; it's the only means for the transmission to "know" how much engine power is being demanded by the operator, since there is no vacuum modulator valve.

        There is normally a half-inch thick spacer between the left side transmission mount and the crossmember. Is that in there?
        Gord Richmond, within Weasel range of the Alberta Badlands


        • #5
          I was suspecting something with the throttle valve linkage after reading through the shop manual. I don't think it would be the transmission mounts since I just had it replaced, but then again - was it put in right? I'll double check. Not sure if there is a spacer - I'll check for it. What does it look like?


          • #6
            It is just a round, cast iron spacer that is slightly tapered smaller upward, larger at the bottom, about 5/8" thick used ONLY on the Left.
            A stack of Fender Washers drilled out to fit the Large Studs will work.

            It IS a good idea to make sure they are the correct Mounts, installed in the correct position, and on the correct side.

            However after reading all of your "Story", the most likely problem is the Throttle Pressure adjustment has been upset by the installation of the Edelbrock.

            In the FUEL SECTION, the Shop Manual describes the correct method of adjusting the upper Carb. linkage to the Bellcrank, BEFORE attempting the Procedure in the Trans. Section to adjust the LOWER Throttle Pressure Linkage to the Trans.

            It sounds like you may have a bit TOO much Oil pressure, the later shift is usually accompanied by a harsher shift especially when using the correct Type "F" ATF.
            Last edited by StudeRich; 03-21-2019, 11:12 PM.
            Second Generation Stude Driver,
            Proud '54 Starliner Owner


            • #7
              Update on the issue:

              I had to drive the car yesterday morning on the freeway to check the issue once more - after applying a considerable amount of pressure on the accelerator to make it to speed on the on-ramp, the car finally went into gear at about 55mph. After that, the car shifted into gear fairly normally for the rest of the trip.

              I spoke with my Stude mechanic who lives in LA about the issue - he mentioned that if this JUST started happening and was not a consistent problem, that is to say repeating itself frequently, that it might not be the linkage but perhaps the governor in the transmission. However, I have my doubts that it's an internal transmission issue because of the following:

              My local mechanic in SD came to visit in the afternoon. He looked at the throttle (gas pedal to carburetor) and noted that when I depressed the pedal all the way down, the upper carburetor linkage (a hollow rod) was not fully telescoped out. After some minor tinkering, and a few heavy stomps on the pedal, the pedal (which is screwed down to the floor) all of a sudden felt like it had loosened up a bit. I could now more fully engage the throttle (the rod attached to the carburetor now telescoping outward fully extended). I took the car out yesterday afternoon and it shifted fine. I took it out this morning, and it seemed fine again. Could this be due to my pedal not being adjusted properly and therefore not allowing full kick down? Is this issue perhaps affecting or necessitating further upper throttle adjustment?


              • #8
                If you are stretching the Bellcrank to Carb. Rod (it has a built-in spring) to reach wide open Throttle the Rod is adjusted WAY TOO short.

                Only the procedure in the Fuel Section of the Shop Manual as mentioned in post #6 will work to get that Rod correct, your friend had no idea how it SHOULD be adjusted, but was correct that it (AND the Lower Rod) are out of adjustment. ...BACK to Post 6.

                Note that the kickdown procedure 3rd. to 2nd. is a whole different thing than a Normal 2nd. to 3rd. medium throttle UPSHIFT. Your first post referred to that being at too High a Speed, how is THAT doing?
                Last edited by StudeRich; 03-23-2019, 10:26 PM.
                Second Generation Stude Driver,
                Proud '54 Starliner Owner


                • #9
                  So I shouldn't be stretching the Bellcrank to Carb Rod at all, or it should be stretching before reaching wide open throttle? There is currently no stretching until I hit the pedal all the way to the floor. All that said, I'm going to consult the notes you gave me and the shop manual to make sure that the rod is correctly adjusted. Could it have just fallen out of adjustment? - this only really became a problem in the last week or two.

                  The upshift is the problem that worries me - it had been happening at around 50mph. After the futzing around with the bell crank to throttle rod and adjusting the peddle a tad the problem more or less seemed solved although I think that just happened by chance and what needs to be done is a proper adjustment of the rod as you described.


                  • #10
                    Really a little early or late shifts do not worry me as long as they are not too extreme and are FIRM and quick.

                    What you SHOULD worry about is; if it does a "Slip Shift", meaning the Engine is spinning up and the shift takes too long.
                    If THAT happens you are damaging Clutches and or a Band and will eventually destroy the whole Transmission.

                    Normally LOW Throttle pressure adjustment, internal leakage, Low Oil or worn parts cause that, NOT Good.

                    About the Stretch Rod you asked about: normally if you have someone push the Pedal to the floor while you watch the Carb. Lever move, the Carb should be all the way open at it's stop BEFORE the Rod begins to stretch.
                    This also prevents damage to the Carb. by not having enough pressure to force the Carb. beyond wide open.

                    This allows the kickdown switch if it were an Overdrive car to activate AFTER or very near reaching wide open throttle and FULL Oil Pressure to the Trans. for the downshift if it is an Automatic as yours..
                    Last edited by StudeRich; 03-26-2019, 12:05 AM.
                    Second Generation Stude Driver,
                    Proud '54 Starliner Owner