I finally understand thanks to
and


http://www.moparmusclemagazine.com/tech ... index.html


Shift points are determined by the following

1) Governor
2) Line Pressure
3) Throttle Valve Position and pressure
4) Shift Valve Springs 1-2 & 2-3


For the sake of this write-up, take governor pressure to be 1 psi per 1 mph....

Line Pressure to be = 90 psi

Throttle Valve pressure to be from 0 to 100% of Line Pressure.

1-2 and 2-3 shift valves are held closed by a combination of throttle valve pressure and the 1-2 and 2-3 shift valve springs.



When you're not moving, both the 1-2 and 2-3 shift valves are closed and you're in first gear.


You take your foot off the gas and start creeping forward.....

Throttle valve pressure will equal 0, and governor pressure slowly creeps up.

When the governor pressure can overcome the resistance of the 1-2 shift spring, the transmission shifts into 2nd.

You speed up some more, and eventually the governor pressure exceeds the 2-3 shift spring and you shift into 3rd.


So the 1-2 & 2-3 shift springs control the closed throttle shift points of the transmission.

As you apply throttle, the shift points become a combination of spring pressure and throttle valve pressure (throttle valve pressure at half throttle is roughly half of line pressure, or 45psi), which will raise the shift points until you're at WOT and you will get the maximum mph for each shift point.


But lets say you don't like where the shift points are......

To lower shift points, you need to:

1) change governor so that the pressure rise is faster, instead of 1 psi per 1 mph, lets make it 1.1psi per 1mph. (60 psi at 54mph instead of 60mph)

2) Decrease line pressure so the the governor pressure will overcome the throttle pressure sooner (no effect at closed throttle)

3) Decrease strength of 1-2 and 2-3 shift springs (will lower closed and open throttle settings)

4) Decrease throttle pressure by adjusting throttle valve so it can't reach 100% of line pressure.


Conversely to raise shift points.

A) change governor so that the pressure rise is slower, instead of 1 psi per 1 mph, lets make it 1psi per 1.1mph. (60 psi at 66mph instead of 60mph)

B) Increase line pressure so the the governor pressure will overcome the throttle pressure later (no effect at closed throttle)

C) Increase strength of 1-2 and 2-3 shift springs (will raise closed and open throttle settings).



The transgo kit raises the shift points by increasing the line pressure(B above), then dialing back the throttle pressure (4 above) to achieve the desired shift points.


Changing the shift points by governor, line pressure or throttle valve pressure will move BOTH the 1-2 and 2-3 shifts together.

If you raise or lower either shift point the other one will raise or lower by about the same amount (i.e. raise 1-2 shift from 3000 to 3500 will raise the 2-3 from 3000-3500 to).



Changing the shift points by increasing or decreasing the 1-2 or 2-3 shift springs will only affect that shift. (i.e. new spring raises 1-2 from 3000 to 3500, 2-3 stays at 3000)

And will also change the closed throttle shift points.



If you want to have the 1-2 and 2-3 shifts to occur at different rpms, or correct for shifts that don't happen at the same rpm (1-2 happens at 3000, 2-3 at 4000), you have to adjust either one or both of the spring pressures.

Stiffer spring to raise, looser spring to lower.

Before changing springs and during, determine the closed throttle shift points so that you make sure the 2-3 closed throttle shift point stays above the 1-2 closed throttle shift point

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Thanks, Ed. That was simple and informative. Good example of an analog computer with some sophistication...

Lou

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Home of Slant6-powered fun machines since 1988