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Old 09-18-2020, 02:26 PM   #1
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Driving on steep mountain grades - I've never done it before in a Class A

I was reading another thread from someone asking about adequate HP for mountain grades, maintaining speeds, etc. I have never driven a Class A through the mountains. I hope to have the pleasure of doing that in the coming year. As I sit here and read some of the things written about maintaining speed and momentum, the use of engine brakes in descent and all, I realize that I really don't know how to properly do either.



My coach is a 2005 Mountain Aire 43' tag with a ISL 400 Cummins and an Allison 3000 transmission. Given all that, as far as going up and coming down, as ridiculous as it might sound to most of you who have done this - whats the best way to do this?



As far as going up, do you just push the pedal to the floor and keep it there for the climb, let the automatic trans do it's thing and go? Do you have to manually select a lower gear to keep the revs up? When they speak of only being able to maintain 45 mph or so going uphill I presume that's full throttle and let the engine do the best it can? Coming from a history of gas only engines, that sounds abusive, but I guess diesels are OK with that?


Coming down I have a two speed (High-Low) engine brake. I presume that as the coach gets momentum coming downhill, you engage the engine brake and comedown essentially at idle power and the engine brake keeps the coach from gaining speed and you having to constantly use the brake pedal to keep the speed under control. How do you decide to use low or high setting?



I'm sure all this becomes self evident as you do it but it'll be nice to have a basic idea going into it.
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Old 09-18-2020, 02:38 PM   #2
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Going up hill--engine RPMs are your friend--with my 400ISL, 1800-2000 RPMs is a pretty good sweet spot[to include good engine cooling], so manually select your gears to stay in that range. Get your speed and momentum up at the bottom of the hill--again, RPMs are your friend....down hill--engage the jake [high setting] at the top of the grade, keep your speed comfortable at the beginning by manually selecting your gears. Some rigs allow you to "feather" the jake on and off with the accelerator pedal to maintain desired speed...you can also use service brakes periodically for short periods to help determine the correct gear for the jake to hold you at the desired speed ...you will get the feel for it pretty quick--just start the process at the top of the grade, and not when your speed is already "uncomfortable."
PS-- some say just let the Allison auto-select the gears but I like to manually control both up hill RPMs and down hill speed--works for me....
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Old 09-18-2020, 02:39 PM   #3
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This will bring out all kinds of replies. Do a search and you will find all kinds of articles for mountain driving. Here is one: https://rvlife.com/tips-driving-an-r...untain-grades/

Another: https://commutter.com/rv-mountain-driving/

And Another: https://rv-roadtrips.thefuntimesguid...ntain_driving/

Again: https://roadslesstraveled.us/rv-moun...ountain-roads/

And a discussion: https://community.fmca.com/topic/225-mountain-driving/
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Old 09-18-2020, 02:42 PM   #4
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Old Scout has pretty much nailed the procedure I use.

Others prefer to just let the trans do the shifting.
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Old 09-18-2020, 02:45 PM   #5
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Choose an engine compression brake setting (Hi or Low) AND the correct gear (use the down arrow) such that your speed is in equilibrium-- you are neither speeding up nor slowing down.


Based on physics, your speed will be faster than a loaded 18 wheeler, slower than an empty one.


If you find you are accelerating, use the brakes firmly enough and long enough to allow you to drop to a lower gear.


Again, this is GRADE-dependent, not curves (slow down more for curves). Said another way the road could be straight for the next 10 miles, yet your equilibrium speed may only be 30 MPH.
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Old 09-18-2020, 02:56 PM   #6
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Nice to see a new driver asking for help before he gets behind the wheel.

Old scout has the right idea.

If in doubt on the decent, get behind a semi and use him to gauge your speed.

Safety first.
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Old 09-18-2020, 03:18 PM   #7
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So, again I realize this probably sounds dumb but I've never done this in a big diesel. I understand that I want to maintain the optimum power band of 1800-2000 RPM. If the coach won't maintain whatever speed I'm looking for (for discussion sake lets say 50 mph) I just keep my foot flat to the floor, max throttle at 1800-2000 at whatever gear holds that and get the rig to go as close to the speed I want it to go as it can manage, at full throttle? Being a gasoline driver all my live, going up hill at 2000 RPM with my foot flat to the floor on the gas pedal seems like a very foreign concept. On a gas engine that's incredibly abusive treatment to the engine.
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Old 09-18-2020, 03:25 PM   #8
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So, again I realize this probably sounds dumb but I've never done this in a big diesel. I understand that I want to maintain the optimum power band of 1800-2000 RPM. If the coach won't maintain whatever speed I'm looking for (for discussion sake lets say 50 mph) I just keep my foot flat to the floor, max throttle at 1800-2000 at whatever gear holds that and get the rig to go as close to the speed I want it to go as it can manage, at full throttle?

First, NOT a dumb question. Hitting mountains without knowing what to do-- THAT would be dumb.



All good, UNLESS, repeat UNLESS coolant temperature starts rising (i.e. the thermostat is no longer able to control coolant temperature even when it is fully open).


When that occurs, you do not want to be at WOT (Wide Open Throttle). Down arrow to a gear where going from 80% throttle to 100% will give you a little acceleration. That 80% throttle at higher RPM of engine's RPM range IS the way to climb if cooling system can't keep up with heat load.


And "emergency cooling"-- turn off dash A/C and turn on dash heater. Fan to MAX. That may make you uncomfortable for a few minutes, but avoid a much more uncomfortable moment when you write a LARGE check for engine repair or are forced to stop in an unsafe location.


Yes, for those with side radiators and hydraulic fans with HIGH speed on the fans coming in 10 or so degrees above thermostat fully open, that higher temperature is the point where you cooling system is no longer able to keep up with your heat load-- BACK OFF.
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Old 09-18-2020, 03:57 PM   #9
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...Good question but point here for uphill grades is to maintain the sweet spot for RPMs and the MPH will take care of itself--you will get what you get at 1800-2000, engine cooling should be at max, and you probably wont be at WOT, as at WOT, the RPMs would eventually begin to drop, signaling the OP to drop down a gear
...going down hill, the jake brake on an ISL is pretty robust....so again, start the process early, select gear to keep you at your "comfort" speed, use the service brakes sparingly, anticipate curves and slower traffic, enjoy the ride....
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Old 09-18-2020, 04:58 PM   #10
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As far as going up, do you just push the pedal to the floor and keep it there for the climb, let the automatic trans do its thing and go?
I use the automatic transmission. I've found my Allison does a much better job of maintaining speed than I do.

I only have an exhaust brake, but no engine/compression Jake brake, on my 350HP which I flip on and off along with occasionally hitting the brakes on the way down. The idea is to keep both the engine and brakes from overheating.

I've learned to keep my water tank level low on mountain trips.

Also, a couple of handy "elevation" resources . . .

GARMIN 780 GPS with Elevation feature:



RV TRIP WIZARD - for trip planning:

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Old 09-18-2020, 06:22 PM   #11
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If I remember right, Mike Cody from Camp Freightliner, gave us a “rule of thumb” is to apply the engine/ exhaust brake if you couldn't see the bottom of the hill, otherwise your service brakes will handle it.

As others have said, don't ride your brakes going downhill, let the speed build up and “stab” the brakes just long enough to get down to a comfortable speed, then let off. Repeat as necessary.

Once your brakes get overheated, you have serious problems!
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Old 09-18-2020, 06:25 PM   #12
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There are two things to avoid: transmission hunting, and using your service brakes.

If you find your transmission keeps switching between two gears, spending only a few seconds in each, you should hit the down arrow until you've selected the lower of the two gears.

If possible, use your jake brake only. If the jake brake by itself won't hold you, apply your service brakes firmly until you are going slower than your desired speed. Then take your foot off the brake pedal. If you find yourself having to use your service brakes more often than every ten seconds or so, you are going too fast. It's critically important that you give your service brakes time to cool off between applications.

I suggest that you focus on those two things first. Once they are second nature to you, then you can start doing things like trying to stay in a particular rev band, modulating your engine brake, etc.
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Old 09-18-2020, 06:53 PM   #13
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Tthree comments:

Old-Scout is spot-on with this comments.

NEVER, NEVER let your engine lug. In short if you press on the pedal and you do not gain any speed you are lugging your engine. You need to be in a lower gear. Here's a reference lifted from elsewhere.

"......There is one firm rule that every equipment operator and truck driver memorizes on their first day: NEVER LUG A DIESEL ENGINE! With the throttle wide open under load, keep the RPMs above 80% of the maximum RPMs. For example, if your maximum engine RPM is 2600, never let it lug below 2000. When you get below that you will drop off the power curve anyway, and lugging a diesel will hammer the rod bearings right out of the engine....."

If you still don't understand engine lugging, Google it.


I leaned to drive in the Rockies and lived here my entire life. To me, you should never feel uncomfortable while driving up or down a mountain road. I will manually shift gears as I feel it's needed. Even more so on the down slope. At the TOP of the decent I will engage the exhaust brake and downshift to slow my speed. It's very easy to allow a little more speed to build up on the down slope but can be hard to drop it. My goal is to never touch the service brakes on the decent unless I really have to. Sometimes I succeed and sometimes I don't. Don't ride your brakes in any case.

Don't fret too much about traffic backed up behind you. If there is a line of traffic I pull over in a safe place and allow them to pass, then continue down. Remember your job is to get you, your passengers and rig down safely not making other drivers happy. Always pay attention to weather changes in the Rockies, it can snow any month of the year on some of the higher passes.
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Old 09-18-2020, 07:10 PM   #14
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Everything I have read for post above is all good advice and there is a few other points I would like to add.

#1 the Allison can be programed to have two distinct shift modes. It can hold a gear to long if the factory didn't consider the HP of the motor and weight of the coach . If you fine your running below 1400~1500 RPM up hill and it will not downshift you should consider going to a Allison dealer to change the TCM shift patterns to better suit your motor. It also can be programed for ECO mode and Performance mode . just by hitting the mode button on the fly. Some engine platforms can be programed to run the cooling fan with the Jake brake to add even more engine braking for down hill use.


#2 be careful on slippery roads and using High engine retard this can cause the rear wheels to slide in snow.
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