By Bryan Couch
Motor Coach Industries

Operators have two basic choices in transmissions when they purchase a new motorcoach: the Allison B500 or the ZF-AS Tronic. Both transmissions are equally intelligent when it comes to warning drivers of a problem.

On MCI coaches, for example, drivers are warned of transmission malfunctions two ways: early-warning dash lights and via the shift-selector screen. If either system activates, a technician should inspect the coach immediately.

Here are a few important maintenance tips for both transmissions. More are available through MCI, Allison and ZF Web sites.

Allison B500/B500R
The Allison B500 and B500R transmissions operate in a similar manner to other automatic transmissions, but with some special features. A pre-selectable shift enables the operator to select any gear at any time, though the transmission will only shift to the selected gear once output RPMs reach sufficient speeds.

While the mode button, located on the shift-selector pad, has multiple functions, its primary function is to allow switching between economy- and performance-shift modes. Economy is the startup mode. It allows early up-shifting to improve fuel economy. In performance mode, the transmission remains in gear slightly longer, allowing for better performance. Drivers can switch between modes even when the vehicle is in operation.

Proper transmission oil level is important. This check is made by using the selector pad display and should be done when the transmission is at normal operating temperature. The display will show one of the following two codes: O,L,O,1 when the oil level is one quart low, or O,L,H,I,1 when the oil level is high one quart.

Transmission error codes also should be checked. If "Mode On" is illuminated when reading any of these codes, it means the code is active and should be reviewed before further operation. A total of five codes can be stored in memory and can be switched by depressing the mode button.

ZF-AS Tronic
One of the newest additions to the MCI powertrain family is the ZF-AS Tronic transmission, which offers greatly reduced maintenance costs. Currently, 30 percent of new coaches are equipped with the AS Tronic, and MCI will soon offer an intarder option with the system.

The AS Tronic has no paper-element filters to service and no oil cooler to replace. The oil capacity is three gallons and only requires changing every 185,000 miles, or every two years.

The AS Tronic was designed to take the worry out of transmission maintenance. The estimated clutch life exceeds 500,000 miles, and the driver's display will indicate "CW" when the clutch finally requires service, which should only be performed at a qualified service center.

Aside from servicing the oil and clutch, no preventative maintenance is required, thanks to a microprocessor-controlled, self-adjusting system.

However, to assure long life and dependable operation of the AS Tronic, operators should carefully review all applicable manuals prior to operating the coach. A few important items to consider:

1. Unless circumstances prove it necessary to use the manual shift mode, leave the transmission in auto mode by simply selecting "D," or drive.

2. Do not attempt to select a gear until the "air low" (AL) indication has stopped.

3. When shifting from drive to reverse, or reverse to drive, first stop the coach. With the service brakes applied, select neutral, then either drive or reverse.

4. The engine must be at normal idle before shifting. If the coach is at fast idle, turn fast idle off and wait for the idle speed to slow before shifting.

5. Select "N," neutral, if the coach will be stopped with the engine running for long periods.

6. During extremely cold weather (-4 to -22 degrees Fahrenheit), allow the AS Tronic to warm up for at least 10 minutes prior to operation.

Bryan Couch is vice president of product development and technical support at MCI.