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Thread: ST-300 modulator ?

  1. #1

    ST-300 modulator ?

    Hello,

    I have a Buick Skylark 1966 with the stock engine 300CI and the ST-300 trans too.
    When I "use" the kickdown, the engine goes up but the shifting takes 2-3 seconds before the kick ?
    There is a strange delay between the moment the engine go fast and the trans shift down.
    Do you think it is the modulator ?
    Or I need to adjust the low band ?
    Or this is the stator and detent switch to adjust ?
    Or...

    Thanks for your help and so sorry for my bad english, I hope you understand my problem.

    Vincent
    Switzerland

  2. #2
    Join Date
    Dec 2011
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    It sounds as if the stator is changing pitch first and then the gearset downshifts. I checked the trans wiring diagram and it looks like the stator solenoid and the downshift solenoid are both operated from the same switch. Because of this, I don't know how you could adjust the downshift timing to make it occur sooner.

    Ray

  3. #3
    The detent switch on the intake manifold activates the the pitch change for transmission converter around 3/4 throtttle and activates the transmission gear kick down at full throttle. A detent switch that is out of adjustment or broken could be the reason for not shifting down. I would see if the transmission is getting 12 volts for both the converter and kickdown at various throttle positions with the key on and the engine not running.
    Steve B.



    67 GS 525 Buick Stage IV
    66 GS Convertible
    65 GS HT
    63 Riv
    02 Subaru WRX Turbo
    03 Ford Cobra Convertible (Factory Supercharged)

  4. #4
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    Steve, I can see that the switch has two sets of contacts, one for the converter and the other for the downshift, but they appear to be mechanically linked inside the switch. Is there any way to adjust their relative timing so that the downshift occurs earlier, which is what Vincent would seem to need?

    Ray

  5. #5
    Yes, there is a procedure in the 65, 66 and 67 manual for the st 300 and st 400. I think bob has the 67 manual on line here. The procedure is the same for both transmissions. It is most likely out of adjustment for kickdown at the end of the throw or broken in that art of the switch.


    Sent from my iPhone using Tapatalk
    Steve B.



    67 GS 525 Buick Stage IV
    66 GS Convertible
    65 GS HT
    63 Riv
    02 Subaru WRX Turbo
    03 Ford Cobra Convertible (Factory Supercharged)

  6. #6
    Thanks a lot for your help.
    I try to adjust the detent switch like they explain it in the 1966 chassis manual.
    I come back on this forum when I have some news about it.

    Best regards to all

  7. #7
    Join Date
    Apr 2018
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    Hayden
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    Stator and dent switch

    Book says; with carburetor in wide open position and switch plunger bottomed. Adjust link until it will slip over carburetor lever pin. Then screw link into plunger 1 1/2 turns. Install washer and retainer. Inside the switch there is a plastic piece with a copper contact that connects to the linkage, it slides in and out making contacts on each end of another copper piece that has contacts that are connected to the power supply. There are contacts similar to a points contact on this part. This is where the adjustment has to be correct. I’ve had same problem working on it now. Opened it up parts fell out.
    Up date, I finished fixing the pitch control switch, it’s working well, has much more torque now than before. I had to do a little shade tree rigging because I couldn’t find a new or reconditioned part but it works, drove it about and hour yesterday no problems yet. It makes the car have lots more toque. Now I’ve got a different problem in my haste to drive the car I left the dash pot assembly on the fender and it in my yard somewhere, I just hope I can find it befor my dogs do. It’s for slowing down the throttle return on deceleration, it’s broke anyway but I can’t find another so I need to find it. Anybody know where I can get one, dash pot? Works fine without it right now maybe I can get by without it.
    Last edited by GrayGhost3480; 04-25-2018 at 07:12 AM. Reason: Up date

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