Engines necessary to periodically start the engine, it is rec- ommended that normal operating temperatures be attained before shutting down the engine. Allison World Transmission Pacbrake exhaust brakes on engines that are used with the Allison World Transmission MD series, are inter- faced with the transmission electronic control module (ECM). An exhaust brake enabled transmission ECM will usually provide converter lockup in gears two through six. Effective exhaust braking begins when the transmission automatically downshifts into fifth gear (62 mph or less).
Once on, the Pacbrake exhaust brake will control road speed and/or slow the vehicle sufficiently that the transmission will automatically downshift, if nec- essary, to Allison’s preselect mode. The preselect mode is normally assigned to second gear; however, the transmission can be reprogrammed by an Allison Transmission Distributor to third or fourth gear should the operator desire. If additional retarding power is required before the automatic downshifting oc- curs, you can select a lower transmission gear on the Allison shift selector. 4.33