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The automatic transmission (C6) in my 66 Fairlane GT/A (390 engine) was recently overhauled internally.

When tested on the road it works fine and shifts up smoothly, however, there is a BIG "but": it won't downshift when conditions require it (a hill, or in general applying a heavier load on the car) and it will not "kick-down" either.

I am sure the cause must lie within the vacumm valve that controls these changes: in my case it is new but I asume it should be set to operate at a very specific vacumm setting.

Would this be the fault?

If so, how can I possibly get the setting correct, so the transmission will work as it should?

Thanks for your help!


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Not sure if your problem is the same as mine, but I'll give it a try....

Is your transmission a "Green Dot" version? Mine was. It seems that Ford had a version with a green dot on the shifter bezel that when placed in the first detent below neutral (green dot at that location) IT WOULD LOCK OUT LOW GEAR!!!! It would start from a stop in 2nd gear and then shift to high. Perhaps it would also change the down-shift points as well. I was told by a Ford mechanic that it was introduced to compete with the old 2-speed Chevy transmissions. If you place the shifter in the second detent below neutral, it would shift normally starting from low gear.


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I thought Fords of this era used a manual kickdown linkage, either a rod or cable, that needs to be adjusted. Has your car been converted to vacuum for this function or am I wrong about that.

My Falcon's kickdown rod got bent once driving in a severe snow storm (ice built up behind it during an extended drive) and I was never able to adjust it all the way back again. It's possible that you just need to adjust the linkage.

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Hello Lars:

I had the same problem on our '66 Mustang with the C4 transmission. Both the C4 & C6 have a vacuum modulator AND a 'throttle lever'. As was mentioned, the modulator controls up-shifts. It ALSO controls downshifts at low speed. At higher speeds (somewhere above 35 MPH), the 'throttle lever' controls downshifts.

Our 289 V8 Mustang uses a short braided steel cable to connect the accelerator linkage to the 'throttle lever'. The 'throttle lever' shaft is concentric with the 'gear select shaft' (PRND21). That short cable was missing & flooring the accelerator would not cause a 3-2 downshift at speeds above (roughly) 35. However, flooring the accelerator at lower speeds would allow either a 3-2 or 3-1 downshift to occur (speed dependent).

As a test, let your C6 up-shift into 3rd under light throttle and before you reach say, 25 or 30, floor the accelerator. A partial flooring should produce a 3-2 downshift while a full flooring should result in a 3-1. See what happens. Your 390 V8 will really pull when that C6 drops into 1st...!

As mentioned, I believe the Fairlane uses a combination of 2 or 3 rods with accompanying pivot points to connect the throttle shaft (at the carb) to the 'throttle lever' (at the transmission). If that linkage is misadjusted (or missing), higher speed downshifts won't occur.

I have a factory shop manual for the '66 Fairlane & can scan a diagram if you wish.

Keep us posted.


Edited by pfloro (see edit history)
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  • 2 weeks later...

Hello: Frank, Daver, Melvin and Paul!

My apologies to all of you for not reacting proptly to all your helpful repliues! I am sorry, I was on a short trip and had no access to the forum (rather an age related technological problem....)

Now I have gone through your very welcome comments and have convinced myself that the blame should go on my linkage, because I in fact believe something is not connected as it should there!!

Will check it out!

Thanks again, all of you!!


PS: Frank, no I don't have the green dot you mention.

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