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Originally Posted by oab_au
The dropping resistor is in series with the A solenoid to drop the 12V signal from the TCU to about 5V to suit the 3ohm solenoid. The standard resistor is 12 ohms the solenoid is 3 ohms, so 0.8 amps flow in the system, to have the line pressure change, to suit the throttle position.
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The resistor circuit has no individual relationship with throttle position. Solenoid A is controlled by means of a combination of signals delivered the full voltage, as well as the resistor circuit. The resistor circuit, due to the reduced voltage, is not capable of properly moving the solenoid.
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If we use a higher resistance of 20.6 ohms, the total series resistance is now 23.6 ohms to flow 0.5amps. This increase will have the line pressure 37% higher than it was. The maximum line pressure will not increase, only the lower pressures are increased.
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Line pressure is adjusted by means of the pulse width and the length of time the valve is open. If the resistance/resister is increased, a point will be reached, whereby the solenoid will not remain held in for a complete cycle. N.B. Altering the resistor can not provide a degree of adjustment.
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This can help a terminally ill box to survive, in helping the band not to slip in 4th at low speed, but it will also increase the pressure to the C solenoid by the same amount, that can cause the transfer clutch to bind at low speed turning.
As for firming up the shifts. The TCU lowers the line pressure when the shift is to take place, so you are not really fixing the soft change, just making it feel better.
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If the resistor is reduced in value, below an optimum figure all control via the TCU will be eliminated. There is no half way or adjustable position.
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The Quick Change does it right. it prevents the pressure drop, and the 50% power cut during the shift, to remove the time lag, and allow the shift firmness to suit the throttle position. Harvey.
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At an intermediate fixed throttle position, the "QC" totally eliminates control of line pressure via the TCU. At and from a specific point any control relative to throttle position, is eliminated.