Gears and Grades Q

So we have a 27 foot school bus with a duramax engine. We’re headed through Montana and all we can find when we try to look up what gear to use coming down the mountains is “use the right gear” or the old “use the gear you used to come up” adage.
Anyone have any input?

Good thing it has an engine but the transmission is a mystery. Please include type and specific transmission. Maybe some drivers have an idea. I was in first when I removed the mirror so goodbye and I have no advice.

Can I presume this school bus has an eaton fuller manual transmission?

I don’t want to sound like a smart alec, but as you’re going up the hill, you should already be thinking of the correct gear going down the hill

You do NOT want to downshift when you’re already going downhill . . . it’s possible that you’ll shift out of gear and won’t be able put it into the lower gear you’re hoping for, and then you’ll be in a bad situation

And if this does have an eaton fuller transmission, do you know if it has synchronized gears or straight cut gears. A stick with straight cut gears is trickier to shift, versus the other other kind. Double clutching is the name of the game, in my opinion

If the bus has an automatic, it’s an Allison automatic, and I’m not sure which model. If it’s got a shift lever, it’s probably a 2000 series, if it’s got push-button, it’s probably a 3000 series. In any case, you shouldn’t be in “D” going downhill, but I would say the next lower setting

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Sounds like an Allison 2000 series. Sorry I don’t mean to be a da this is just all brand new.

Move the shift lever at least one position down from “D” when going down hill

you don’t want to gather too much hill going down these hills . . . presumably quite steep?

Does this school bus have air brakes?

If so, it’s extremely important to be in an appropriate gear, because you definitely don’t want to run out of brakes, so to speak

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Diesel engines don’t engine brake effectively unless they have an exhaust brake or are of late model with integrated exhaust brake.

In any case the engine should be operated within its design limits. A diesel engine should not be operated above 3,000 RPMs. When down shifting to control the vehicles speed, chose a gear that keeps the engine within its design limits.