I really didn’t wanna go down this rabbit hole, but I can answer a few things below. I have given this a lot of thought and a lot of work and I believe I have the kick down set up correct. However, it might be a little aggressive and that may be what you’re referring to, and I certainly can dial it back. This is what I wrote in the 4Bbodies in my restoration page.
Here is a link with pictures:
1970 Plymouth Sport Satellite from Junk to......
The kickdown (KD) assembly is based on the original set up. With an altered intake manifold and carburetor it’s a challenge to get the original rod type of KD set up correctly. This is why many people go to a cable set up. I like the stock rod type linkage and wanted to keep it that way.
The issue/resolution I had was two fold.
1. I didn’t know that there is inherent play/slack in the KD lever at the trans lever moving through the KD linkage all the way to the carburetor. This means no initial trans throttle valve engagement until you’re well past 20-40% of the KD travel. This slack needs to be taken out!
So just having the KD set to move just as the throttle moves is not how I have determined it should be set up. You must take out most of this slack in the KD so it engages sooner/faster! It’s nuanced, but important the kick down valve needs to be asserted right away and that slack prevents that from happening.
2. The stock set up the ratio is very close to one to one 1:1. However with a 2-4 barrel carb conversion and subsequent intake manifold change the ratio is off quite a bit and more like a 4:1 from what I found on my set up. This requires a ratio change and subsequently a longer horizontal KD rod and a longer vertical rod to accommodate this ratio change.
There are several ways to accommodate the ratio change. One can use a longer lever from the transmission arm, or changing the ratio at the bell crank upper or lower. I’m modified the upper bell crank because it’s right there and you can get at it easily.
Most importantly one must to alter the ratio. To do this I made an extension on the bell crank. It’s extreme but thats how far off it needs to be when the slack is removed and hence total travel of the KD is reduced compared to the total travel of the throttle. They must end up matching or else one will bottom out BEFORE the other which is no bueno.
I simply made an extension bar for the upper bell crank with two bolts so it’s not a permanent modification. You can clearly see this in the pictures below to the right.
To accommodate this ratio change I used a 2” spacer on my vertical rod and a custom/longer horizontal rod that I fabricated. Note the horizontal bar needed a specific bend in order to clear the air cleaner assembly during actuation.
Now it works as it should. As soon as the throttle starts to move the KD starts as well. The slack is gone and they both reach full throw together! The shift points are now correct as well which is the proof in the pudding.
At some point for aesthetics I may make the modifications at the lower vertical bell crank and get the upper bell crank back to stock.
Just found this in the fsm. This is what I wanted as a reference. No 340 but it ballparks me.
My specs
28” rear tires
3:55 rear gear
340 high compression solid lifter
No cam spc but definitely not stock
