First time mountain grade @ 6%

[tgr1605]

What is the safe mode to ascend and descend? Let the allison tranny and the pac brake do the work or maybe do the grade in 4th or 5th. Ohio to Georgia Jellico Mt

8.3 Cummins Allison 6 speed

[dennis45]

Originally Posted by tgr1605

What is the safe mode to ascend and descend? Let the allison tranny and the pac brake do the work or maybe do the grade in 4th or 5th. Ohio to Georgia Jellico Mt

8.3 Cummins Allison 6 speed

Here's a Rule of Thumb.

Don't go down any faster than you could go up. Which means, if you go up in say third gear, go down in third gear.
The transmission will want to upshift when your speed increases to prevent engine over speed. So when it upshifts from your selected gear, firmly apply the service brake to lower your speed and the transmission will downshift back to the selected gear. Do Not pump the brakes. This will cause overheating and usually does not end well.
Firmly apply the brake to reduce momentum then release and let them cool. A 6% grade is a piece of cake and a good one to practise for the 8-10% grades that will keep your attention.
Do not worry about holding up traffic. Stay focused on the task at hand and ignore the impatient ones behind you.

Safe Travels.

P/S, going up, the best is to select the gear that holds the engine RPM in the 2000-2200 RPM range for peak torque and cooling. On Short grades you can let the Allison do it's thing but long grades it's better to manually control your speed and engine RPM.

[bamaboy473]

Don't let the engine over-rev or fall below the peak torque curve. Selecting a gear manually is what you do if the coach will not stay in that peak condition/revs.

Pump brakes as needed if you continue to increase speed down the hill, but don't ride them.

[Pepper2]

Originally Posted by dennis45

Here's a Rule of Thumb.


A 6% grade is a piece of cake and a good one to practice for the 8-10% grades that will keep your attention.

Safe Travels.

Good advice. My first experience with these grades was last summer and I was terrified, turned out my fear was unfounded.

[dennis45]

Originally Posted by Pepper2

Good advice. My first experience with these grades was last summer and I was terrified, turned out my fear was unfounded.

6% grades in our part of the world are just little hills.

[brandss]

We are brand new to a DP but here is what we did on our trip from Phoenix, AZ where we got our first coach to back home to KY. Watched a video (1 of a million) and a professional truck driver said in the video to let the engine do the work coming down a grade.

Going up if it was short we let the bus do what it did, if it was longer we went into manual and shifted to a gear to keep us around 2300 RPM's. Going down, and we normally had the cruise on up and down, we let the tranny do the work. We rarely had to touch the brakes and we would use cruise control going down to keep the speed to a very safe speed. The air brake was/is an incredible thing.

I will be anxious to see if I'm blasted by our method since we are still learning.

[wfalch]

Try the grade going from California to Oregon on I5 or do it in the reverse.

[NHRA225]

Jellico is a piece of cake going North or South .
Heading south I usually stop in that last rest area and have lunch and cool down. heading out I build speed on up to 65 or so and begin to let my Allison choose her gear-- usually 4th and cruise on up @ 55 mph or so - not in a big hurry .
Now Asheville NC is a whole different story =7 % down -- Pac Break on all the down - 6 miles or so --35 mpg All the way --Rpm 2200 and hit the Brakes every 30 to 45 seconds or so .
You'll be fine --Just take your time.

[Finance]

Never pump airbrakes. That's how you deplete the air pressure and end up with no brakes.

I hope the previous poster meant to say apply brakes intermittently, say for example 3 seconds braking then 30 seconds off brakes to let them cool. Just like hydraulic brakes in that regard.

Pick a gear where the exhaust brake does most of the work, whatever that speed is.

[CountryFit]

Originally Posted by Finance

I hope the previous poster meant to say apply brakes intermittently, say for example 3 seconds braking then 30 seconds off brakes to let them cool. Just like hydraulic brakes in that regard.

No! He didn't mean that, and most experienced RVers know that it shouldn't be like that.

Give the OP an example - on a very very deep slope, say the speed limit is 50mph. At the hill top, you start with engine idle and PacBrake on. Your RV'll creep and get momentum. As soon as it reaches at 55 mph, you apply service brake, with your full force to let it slow down as fast as possible. When its speed drops to 45mph, you release your foot, let engine idle, and let it creep again. Repeat this until you don't have to. Note, this procedure is for a uncontrollable scenario.

For a 6% slope, you don't need to do above. Once you turn Pacbrake on, the gear will drop to 4th or 2nd (make sure the RPM needle isn't in the red area) you should be easy down.

[Smitty77]

It's so easy to over generalize our answers, when the specifics of the combination of many different factors will dictate the best approach to hill climbing, and decent. (Weight of coach. Specific engine, say like the 8.3 like the OP's, with Exhaust Brake Assist vs say a CAT15 with 2 Stage Jake Compression. Gearing of coach. Drums vs Disc brakes. Etc., etc.) What is good input for one specific coach, could be dangerous to someone driving a coach with totally different parameters.

Getting the engine serial number, and calling to get that specific engine's operating parameters, is a good move for any owner. Max HP/Torque. Max RPM. Max RPM with Exhaust or Jake Compression.

A few general observations, from many of you and others over the years, has helped me over the years:

-On hill climbs. The ECM's of engine and transmission 'react' to grade changes. Us who are driving, have our eye's to see the change of grade ahead. So we can pro actively downshift to maintain the optimum RPM for our specific engine. Which us usually relatively close to Max HP RPM. While climbing a hill, if our coach will not say hold the speed in say 5th gear at the Max HP RPM, once it's dropped about 100-150, maybe even 200 RPM's below this Max HP RPM, manually downshift. (Experiment, as this will vary based upon tire sizes, and rear end gear ratios.)

-Learn to reach over and on your specific coach, feel the transmission keypad, and memorize it's layout. So that you can reach over and Down/Up shift, without removing your eyes from the road.

-On down hills. I do understand the rule of thumb mentioned about going down as you came up. But way too many times, the decent is totally different then the grade, and or number of curves compared to what you may have just climbed! So, sure keep it in mind. But again use your eyes, and judge what is ahead of you. (We like the Mountain Directory (East or West) for Trucks and RV'er's. It gives you a good feel for what to expect on both climbing, and descending.)

-As much as possible, use the combination of you're engines compression and transmission gearing to try to hold your speed. Limit your braking, if at all possible. That being said, a big difference in what a BIG BLOCK 2 or 3 Stage Jake Compression combo of Braking Horsepower is, compared to a Small or Medium sized block engine, and Exhaust Assist braking's Braking Horsepower will provide. (CAT C7/C9 and Cummins ISB, ISC and ISL are Small to Mid Block sized engines. I consider anything above 10 liters, to be the entry into Large Blocks (Many will say it's 12 Liters and above, and that's OK!). But take say a BIG BLOCK ISX engine, 12 or 15 liters, but in this example, the 15 liter - lots of Braking Horse Power via Jake Compression!)

-Since their are so many variables in our coaches engine sizes, and again Jake Compression vs Exhaust braking, along with Drum vs Disc brakes - learning how your coaches combination of Braking Assist, and actual braking, work with each other - is an important step of learning your coach.

-I personally, when to able to maintain a desired down hill speed while using my Mid Size ISL with 2 Stage Jake Compression. Like to firmly apply my brakes, and slow down to about 5MPH's below my desired speed. Example If I'm truing to 45MPH in 4th gear, and in High Compression Braking position. Once my speed gets up to a max of 50MPH, I firmly brake until my MPH is dropped down to 40 MPH. (I use common sense on picking the speed I allow my coach to go up to above my desired speed. Based upon is it a straight downhill say vs curves with slower speeds dictated. I also watch the grade changes. If I see it's getting to a steeper decline, I might brake at say 48 or even 47MPH.). But the key, is to slow your coach down as relatively as fast as you can, to a speed somewhat below what you feel is what you want to hold (And not always the posted MPH's, as they are for cars, unless specifically calling out Truck MPH too, and do follow the Truck posted MPH limits.). Then get off that brake pedal, so the drums/pads or disc's can cool down.

And practice. Go learn your coach. Always drive within your comfort zone. Don't worry about people behind you. SET YOUR FLASHERS ON, if going up a hill to slow, and or down a hill too.

This is not a race. And with 30 up to 55K pounds of coaches under our seats - driving for safety and for your rig, is a skill to master.

$.02!

Be safe, have fun, and learn the specific's of your coach!
Smitty

[Mr_D]

Nice write up Smitty!

[IASM]

To add to this thread.
Dont be afraid of grades. You do have to understand your weight. its the old e+mc squared. Speed is the driving factor and you will get a feel over time. Your pac brake is an exhaust brake so higher rpms offer better braking . a slow turning engine is not using much energy pushing air thru the exhaust tube flap.A diesel has no carburetor so there is no resistance other then the flap on the pac brake or the exhaust valves on a jake style.You might find 3rd gear at 1800 is 40 miles per hour. You can check while driving on flat ground what gear and speed at close to redline so you have a quide line.

Watch truck traffic. you dont need to be passing trucks going downhill. They know the road and are managing there speed without using any brakes.
I likely have more jake hp then most but did have an inspire with a c7 and exhaust brake and could manage my speed effective. another trucker trick is turn on your ac. that will activate you fan providing about 30hp more braking.
In my younger years i drove heavy haul sometimes grossing 600,000 lbs. A 6 percent grade with a load like that it was about 20 miles per hour full jake giving around 700hp and i could manage my speed by turning the fan on and off . it get that close.Brakes turn energy into heat. once the drums have sucked up the heat your done until they cool down and that takes a half hour.
I am not trying to scare you. its no big deal. just keep the speeds way down until you know what you can get away with on your setup. If you have to ride your brakes your likely going to fast.

[rampage42]

Dennis45 nailed it. NEVER go down faster than you could go up.
I learned this the hard, dangerous and expensive way!