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Kick Down or Not?

A late shift won't hurt the trans., but may be too high an rpm for the engine. That can be worked on with governor adjustments but that's tricky to do. I have found that usually the linkage needs to be adjusted so when the carb is at WOT you have just a bit more room to push the throttle pressure linkage back a bit more. I leave a bit of room so the linkage isn't forcing the trans. lever further than it's allowed to go.
 
On mine, I'm running the Bouchillon cable setup and with the trans portion of the adjuster bracket full back to the firewall, it also shifts at higher mph for both 1-2 and 2-3 like that. If I move it too far forward then it shifts soft or very quick which is no good. For my cable setup it's a fine line.
 
In all automatics there are a number of different fluid pressures that are separate systems within the trans. The oil pump (or 2 if used) will supply unregulated pressure to the pressure regulator. From there these systems use different pressures for different jobs. For example, it takes more pressure to hold certain geartrain items in reverse than forward gears, so that "Line" pressure will be increased in reverse gear to allow bands or clutches not to slip. "Throttle Pressure" is what the kickdown linkage is involved in. At light throttle input throttle pressure is lower, and this helps to create normal, softer shifts for passenger comfort. At higher throttle openings, increased engine torque demands the clutched and bands to be applied faster and with with greater pressure to lower slippage between shifts. The whole key to this is "throttle pressure" increases with more engine load. Governor pressure is another type of fluid pressure that dictates when the transmission will upshift or downshift, dependent on engine load (directly affected by throttle pressure). "Kickdown Linkage" actually is referring to this same mechanical connection from the carburetor to the throttle pressure valve inside the transmission. Although we commonly refer to this as "Kickdown Linkage" (and it does have a say in kickdown) it more correctly should be addressed as the connection that controls throttle pressure. If there is no linkage installed an internal spring on the valve body will force the internal linkage to return to a kind of "idle" position, making the trans think there is very little or no throttle being applied. So if the trans "thinks" the engine is under low or no load when in fact it's at full throttle, you can see how the clutches/bands would be under heavy load with insufficient throttle pressure to prevent slipping. That in a nutshell is why we need that linkage. If you have a full manual valve body modifications to the valve body eliminate the need for this linkage.
MoparMur knows what he's talking about. I've overhauled a few hundred automatics at the dealership. They all work basically the same. Some use vacuum modulator and kick down linkage to determine engine load others just a throttle linkage but either way it needs to be hooked up and adjusted properly. There's a little hole for a rig pin in the bell crank linkage at the back of the intake manifold that helps you adjust the upper and lower linkage rods properly. As I remember it takes an 1/8" drill bit. The adjustment is all in the factory shop manual. Good luck.
 
Thanks StrokerSpanky. And you just taught me something - I didn't know about the hole in the linkage and drill bit. Gotta love this place!
 
A late shift won't hurt the trans., but may be too high an rpm for the engine. That can be worked on with governor adjustments but that's tricky to do. I have found that usually the linkage needs to be adjusted so when the carb is at WOT you have just a bit more room to push the throttle pressure linkage back a bit more. I leave a bit of room so the linkage isn't forcing the trans. lever further than it's allowed to go.
Thanks again for all the info, I was totally in the dark on this system and it's effect on shifting/trans functioning. I'm just now getting ready to set up the cable for the throttle pressure, and this last nugget is just what I needed. :thumbsup:
 
When they did my trans. RMVB with no compression braking in first. They also had to remove the governor.
 
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