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Old 06-07-2018, 06:33 PM   #1
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How to drive a steep downgrade?

I have a 36' conventional bus with a Cummins 5.9 engine and an Allison 2000 transmission. The engine is governed at 2500 RPM and the speed is governed at 60 MPH. No retarder, jake brake, or magic magnetic driveshaft thingie.

I understand "stab" braking (coast until you hit your max desired speed, brake with gusto to get it down 5 MPH, rinse and repeat). I also understand poking my way downhill rather than letting the speed get up at all.

I have heard that downshifting is a good trick to know. I also think that the transmission will not cooperate if the downshift puts the RPM too high. But while I can grab the gearshift and click it down one more notch, I don't know how and when (or how much) to downshift.

Can someone give me specifics as to what to do so I don't need a runaway ramp? We'll be crossing the Rockies with the back loaded with dressers, piano, and a cow (well, in a freezer).

Thanks!
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Old 06-07-2018, 06:43 PM   #2
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Shifting down one gear will not allow the bus to pick up as much speed.
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Old 06-07-2018, 07:57 PM   #3
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Quote:
Originally Posted by o1marc View Post
Shifting down one gear will not allow the bus to pick up as much speed.
OK, so do that at the top of the hill, presumably, and try to never pick up excessive speed in the first place?

I have "OD, D, 2, 1" or some such. Just take it into Drive instead of Overdrive?
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Old 06-07-2018, 07:59 PM   #4
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Originally Posted by Dapplecreek View Post
OK, so do that at the top of the hill, presumably, and try to never pick up excessive speed in the first place?

I have "OD, D, 2, 1" or some such. Just take it into Drive instead of Overdrive?
Yes, maybe even 2nd if the situation calls for it.
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Old 06-07-2018, 08:00 PM   #5
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Put it in 2d gear, not Drive or Overdrive, before you start down hill. Then, stab braking.
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Old 06-07-2018, 08:02 PM   #6
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Put it in 2d gear, not Drive or Overdrive, before you start down hill. Then, stab braking.
And this is from someone who lives in the Rockies. Thanks, pal!
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Old 06-07-2018, 08:03 PM   #7
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It kind of sounds like you've got it, everything you spoke of is pretty much what I do the only thing I would add is that I would actually pull off the highway when space was available, and let the brakes cool down and give the engine a chance to rest I'm talking about on the big downstroke of the mountain. A few years back I went from Minneapolis up through Montana Idaho Utah Washington and Oregon... I cringed every time I saw a sign that said semi-truck chain up pullover area... That meant there is a mountain coming and there was probably 25 or more 3 to 5 Mile pulls up the mountain the only good thing is you got to come down the other side and I'll tell you a little trick you might be afraid to do this but there's a thing called Georgia Overdrive which means when you can see what's coming at the end of the road like a long straightaway put it in neutral and let it roll. My bus would over rev if I left it in gear at 75 miles an hour in neutral I could do 85... Passing all the semi trucks that passed me on the other side this sounds really dangerous and I'm sorry but it's what I did and it was a blast.
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Old 06-07-2018, 08:07 PM   #8
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AND if you're going downgrade and stab braking, PUT ON YOUR FLASHERS.
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Old 06-07-2018, 08:13 PM   #9
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They'll hear me screaming, too...
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Old 06-07-2018, 08:15 PM   #10
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Will they need a pry bar to get you out of your seat?
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