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Allison Automatic generally makes good transmissions - *FOR THE SERVICE FOR WHICH THEY ARE INTENDED*. We're talking about school bus, some transit buses, straight truck, yard switchers, and even giant off road dump trucks.
The AT545 is an old transmission, built in the days of all mechanical engines. They served well on school bus routes because they did a lot of stop-and-go. They were *DESIGNED* for it. Yes, yes, I know some school districts and routes had their share of difficulties, but I submit that pencil-pushing bean-counters tried to have the buses spec'ed in a way that was supposed to save money (fuel efficiency) at the cost of performance. Another subject for another discussion ...
These transmissions weren't designed for hauling heavy loads up steep mountains at highway speeds. Transmission coolers can be added (and will help extend the life greatly) but ultimately it's not their intended role. Many newer Allison designs are better engineered for this. They are more designed to help improve fuel economy (and do this to an extent), lowering engine RPM at highway speeds. These days some routes are longer than they were in the 70's (when the AT545 was about the only thing available) and it simply makes sense to save every gallon of fuel that you can. It's more of a side benefit that these transmissions are better able to handle highway cruising and towing (within reason). I wouldn't expect to move a 65,000 pound road trailer with a school bus transmission - at least, not far, and not daily (and maybe even not at all).
Yard trucks are very geared down and the Allison transmissions (even those mated to the common 12V Cummins engine) are designed for this task. And even the giant rock quarry trucks that have automatics, these transmissions were made for the job.
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