02 Allison Transmission Operation

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2021 Allegro Bus Chassis: Chapter 2

Driving Conditions

• Normal driving – best fuel economy

o Select “D” and “Mode On”

• Performance

o “Mode Off”

o For mountain driving, select lower gears to maintain 2000+ engine RPM

• Hill climbing on hot days

o Keep RPMs high to cool engine

Driving Tips with the Allison 3000MH or 4000MH Transmission:

The points at which shifts occur depend upon predetermined speeds and other operating conditions. A transmission “shift calibration” includes several sets of shift points used according to current or anticipated operating conditions, such as engine or transmission fluid temperature. You can change shift schedules using the MODE button.

The transmission control module (TCM) includes the capacity for two separate and distinct shift calibrations, one for use in “Primary Mode” of operation and one in “Secondary Mode.”

Primary – This shift schedule is typically used for all normal vehicle operations.

Secondary – This is an alternate shift schedule that the TCM uses upon request. This is operatorcontrolled using the MODE button.

When you are driving under normal road conditions, the DRIVE mode is recommended for the best performance and fuel economy. The MODE switch should be set to ON for economy mode, but MODE off should be used when climbing hills and when extra performance is required.

The display screen on the shift control pad will indicate the highest selected gear for the transmission. When mountainous or up-and-down terrain conditions are encountered, you should manually select a lower gear, preferably lower than 5th gear. This can be done at any road speed by pressing the down arrow repeatedly until the desired gear is indicated in the window of the shifter pad. When your road speed decreases to a safe point, the transmission will downshift at a higher RPM than normal. This will decrease the use of overdrive while pulling hills, which can result in excessive heat build-up in the transmission, and keeps the engine operating at peak horse power and performance.

When ascending a grade, maintain engine speed to within 400-500 RPM of governed engine speed. Governed speed will be 2200 RPM on the Cummins ISL engine model. Road speed may decrease, but the engine will be at its peak in the power curve.

It is especially pertinent to monitor your water temperature gauge when climbing steep grades. Keep in mind that it is not uncommon for the temperature to increase, especially in hot weather. If the gauge reaches 225°F or if the temperature warning light on the gauge panel should come on, reduce your road speed, shift to the next lower gear and keep your tachometer within 500 RPM of engine governed speed. In many cases this will stabilize the water temperature. If the temperature gauge continues to rise, or if the stop engine light comes on, pull to the side of the road and shift the transmission into neutral. Bring the engine RPM to 1,700—2,000 RPM until the temperature drops down into the normal range. This should occur in a relatively short period of time. If the temperature gauge does not begin to drop, stays in the red zone, or continues to rise, shut down the engine and allow it to cool. After the engine is allowed to cool check the fluid level in the reservoir and add coolant if needed.

A good “rule of thumb” for descending grades is to never use a higher gear than was used to climb the same or similar grade. Try to keep the engine within 500 RPM of governed speed. This will give the best engine braking and reduce the need to use the service brakes. Select a gear that will keep you at a safe speed with minimal brake application. Never ride your brakes when descending a grade since excessive brake heat will build up and your brakes could fade, leaving you with little or no braking power.

Your vehicle is equipped with an engine brake. The engine brake will assist in slowing your vehicle on a downhill grade. With the engine brake switch in the on position, release the accelerator and depress the service brake to activate the engine brake. When the engine brake is activated the transmission will pre-select a lower gear to aid in braking. This is indicated by a “2” in the left hand pane of the transmission shift selector. The transmission will begin to down-shift as soon as the road and engine speed will safely allow. This will produce a slowing effect and will remain engaged until ether the exhaust brake switch is turned off, the accelerator is pressed, or the engine speed drops to 800 RPM. If your initial speed is high, you may have to step on the brake to slow the vehicle before the transmission will down-shift from 6th gear to 5th gear. This is normal.

Always select (N) neutral on the transmission shift pad prior to turning off the vehicle engine.

Fluid Level Check

Use the transmission shift pad for best results in checking the transmission fluid level. The transmission will not reach operating temperature until the coach has been driven for at least 15 miles. Therefore it may be best to check transmission fluid level at the end of your driving day.

Transmissions do not consume fluid. If your transmission shows to be low of fluid it should be inspected for leaks.

Check the transmission fluid level with the following steps:

Conditions that must be met

• Be sure transmission is at operating temperature (104° to 220° F)

• Vehicle is parked on level ground with the parking brake is set

• Transmission in neutral and engine at idle

• Wait until vehicle has been stationary for two minutes

• Simultaneously press the up and down arrow keys