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Shift Delay – Why does my transmission seem to “hang” or delay upshifts when cold?

April 26, 2017cold delay hang shift transmission

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Shift Delay – Why does my transmission seem to “hang” or delay upshifts when cold?

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A. On diesel powered trucks, the Allison transmission has a feature to shorten engine / cab warm-up times. This feature is called Heater Performance Mode. This feature raises part throttle upshift points (2-3, 3-4, 4-5) to increase engine speed when cold weather conditions are detected. In addition, the torque converter clutch (TCC) will not apply below a transmission sump temperature of 31°C/88°F. This also aids in warming the cab more quickly. Under these conditions, it is normal to experience upshifts that seem to “hang” or be delayed.