ALLISON MD 3060 AUTOMATIC TRANSMISSIONS

Allison MD 3060 Automatic transmissions are electronically controlled and the only transmission we use in our school bus fleet.

The one element these transmissions do not get along with is moisture which causes problems like crossed signals and fault codes. In our Thomas ER pusher buses the engine and trans. are located in the back end where all the moisture, salt, dirt etc. is sucked up like a huge vacuum. Wiring is another problem, mainly from rubbing along the frame and constant vibration from being encased in plastic loom.

Of course these problems are not caused by the manufacturer, the Allison MD 3060 is an excellent design that monitors every input and output and adjusts transmission operation instantly when required.

Below are some pics of the PRO - LINK, the diagnostic tool needed to troubleshoot these transmissions.

Checking For Fault Codes is the most important procedure in the troubleshooting process.


Hooking up Pro-Link to data link found under dash, the very first step... gathering information.

On-Board Diagnostics

Allison MD 3060 Electronic transmissions require a'Pro-Link' reader for troubleshooting purposes. This tool connects to a data link that will tell you what's going on with the trans. including trouble codes, temperatures, clutch engagement, rpm's, throttle position and much more.

The Pro-Link also performs on-board troubleshooting with action requests. With pressure guages hooked up to each clutch pack pressure port, we can use the Pro-Link to engage whatever clutch we desire while the bus is stationary. Comparing each clutch pressure reading to main pressure indicates if there is a worn clutch pack, which will cause excessive heat and slippage.

This tool is invaluable and without it you're pretty well sunk unless you can physically find open or shorted wiring. We have been finding a lot of faulty wiring from the Electronic Control Module to the transmission externally mounted speed sensors and Throttle Position Sensor. The wiring is a twisted pair so we replace it all, with new shielded wiring. This is much faster compared to finding where the exact fault is and doing a spot repair.

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THE NEW FREIGHTLINER C2 MODEL

This the first one in our school bus fleet and so far it's been met with positive feedback from our operators. What I like about it is the headroom, in the older buses I've caught my hair in the roof seams many times! The engineers must have heard my cries.

The Mercedes MBE 900 engine is performing well at 230 horsepower. Time will tell how this engine responds to the demanding stop and go driving habits and our below freezing weather.


They come with a diesel fueled coolant heater and automatic pre-trip system, the operator just has to casually walk around the bus while the exterior lights and stop arms go through the motions.

These buses are quieter than the older Freightliners, a common complaint from drivers is cab noise.

We are currently changing the oil on all our electronic diesels at 15,000 km [9,000 miles] and taking oil samples for analysis. No problems have arisen since we started this program.
I recommend finding out all you can about Motor Oil & Engine Filtration, it will save you a bundle!

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The principles of a diesel engine are very basic but certain conditions must be met before ignition occurs.

• Extreme heat
• High compression
• High pressure atomized fuel injected into the cylinder at the right time.

This scenario is performed inside each cylinder of a diesel engine at high rpms and under heavy loads.

The INTAKE valve opens allowing air into the cylinder on the piston downstroke.

Both valves are closed on the COMPRESSION stroke creating extreme heat and compression in the cylinder, as the piston comes to top dead center the injector delivers a high pressure spray of atomized fuel. Fuel delivery timing is essential at this stage.

This causes an explosion in the cylinder and the POWER stroke comes alive.

As the piston comes up once again the EXHAUST valve opens, pushing out the previously ignited gases.

This a simple over-view of a 4 stroke diesel engine.

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Greetings!

Welcome to the very first post of my 'School Bus Mechanic' Blog!

My name is John Whelan, I live in Kamloops, B.C. Canada. My day job? Heavy Duty Mechanic for the Kamloops School District. Repairing and maintaining a fleet of 70 school buses and numerous support vehicles is what I do, along-side the other mechanics I work with.

Today's school buses are far more advanced than you may think. The diesel engines and transmissions are all electronic with on-board computers that monitor emissions, driveability and faults.

There's still the typical 12 volt systems, air brakes, steering and other components that make a school bus run.

Here's the plan; I will be taking my digital camera with me and taking daily photos of our operation, giving you a rather interesting insight into the daily happenings of a typical school bus garage!

I've always wanted to do this as no one really knows what a School Bus Mechanic does all day. Some jobs are easy and others aren't but that makes the job interesting with lots of challenges filled with variety.

Sharing some AHA! moments will make postings even more interesting, troubleshooting faults and problems can be painstaking but always thought provoking!

After working in this trade for 28 years it's nice to be able to pass on my knowledge and experiences, both past and present.

One thing for sure, no one knows everything; Technology is always changing, humility and patience is needed when it comes to learning something new.

I'm hoping curiosity seekers, other mechanics or bus owners will leave a message or two and have some input or ask questions. There are no barriers or restrictions here, everyone is welcome!

Thanks!

John Whelan