Driving on steep mountain grades - I've never done it before in a Class A

[Winemaker2]

Originally Posted by BobRay

3. The old adage about using the same gear coming down that you used going up is nonsense. One side of the mountain may be *much* steeper than the other.

Originally Posted by Winemaker2

I'm surprised I didn't see it above but a rough guide for descent
(of same grade as ascent)
you will want to use the same gear required to climb the same grade.

The operative phrase is "SAME GRADE" seems obvious that there is a need to adjust for greater or lesser grades but maybe need to spell that out.

[96 Wideglide]

Originally Posted by mlpeloquin

I always use the Jake full time. It save the breaks. If going slower than the posted speed limit, use your flashers so that anyone coming up behind you is warned a head of time. Do keep it at or around 1800 RPM. That is even if you are slowed down to 30mph or slower. With your setup, you should never get that slow ever. A good reference is to go down hill at the same speed as up hill. The grade is usually the same. Not always, but with time you will be a better judge. Do not get complacent. Always error on the side of caution and safety.

I'm guessing when you say 1800rpm's, you have switched to talking about climbing, not descending.
1800rpm, doesn't give you much engine braking.

[richard5933]

The adage about using the same gear going down as going up obviously requires the driver to use some common sense. It was also started in the days when most people were driving a manual transmission like I am.

If you had to downshift to 2nd gear to make it over the crest, the thought was that you stayed in 2nd. Some untrained drivers would hit the crest and immediately start upshifting as things flattened out for a minute, then disaster struck as they realized they were on the downhill side before they could do anything about it. Not as critical a mistake in an auto, but still something to keep in mind.

The adage still applies though - if you climbed a steep grade and had to push the auto down to a lower gear, when you start down that same grade on the trip home you should have made a mental note of the need to keep your speed down and be ready to hit the downshift button.

Driving a heavy vehicle on steep grades is not a hands-off experience. The driver needs to maintain control of speed at all times and not rely on the technology alone to do it for him/her.

[Ray,IN]

Originally Posted by Cougarkid

Someone can chime in and let me know the answer to this.....
Do the ISL’s have built-in regulators to control exhaust gas temps?

I have a 1998, Fully mechanical 325hp, 8.3L Cummins/Allison 6-spd . I live and die (climb) by the boost and the piro (exhaust temp) gauges. Downshift, adjust throttle, control boost, control temps by those gauges.

One thing not mentioned, but note worthy.
With a gas engine, the (more) gas you are dumping in a actually helps cool the engine.
With a diesel, as you dump more fuel in (pedal to the metal), you INCREASE the engine temp. That is why backing off the gas will help bring engine temps down.

Just my 2CW.

CumminsRV ISL engine is 8.9L = L9 engine. ISC is 8.3L. The ISL is a stroked ISC engine.

[GJohns]

When descending Wolf Creek Pass in the Rockies, we called Allison before we left. They said just let the trans do its job and you’ll be fine. And we were! We also use the books Mountain Pass West and Mountain Pass East to give us the best idea of what we’re faced with. Available from steepgrade88@gmail,com for $16.99 each or call 785-594-2489 to order.

[Doug427]

Since I have fully fallen on my sword to the point of impaling myself on it in admitting my ignorance in all this, I'll ask another question that is probably very obvious to all of you but not to me.My engine brake (Jake?) is a two setting affair - high and low. How does one determine which setting to use? I know nothing of this device called Jake.


By way of explanation, this is my first RV. I have never driven a large diesel vehicle before. I spent the first 50 years of my life on Long Island, NY where it's as flat as a pool table. I then moved to Houston for the last 11 years, where again, it's as flat as a pool table. That's my story and I'm sticking to it.


I figure it's better to sit here safely at home working this all out thanks to your expertise and generosity helping out the new guy, then bombing down a mountain out of control wishing that I had asked.

[J2battle]

Hi Doug. If you’d like to contact me by private message at jeffbattle@me.com, I’ll help you.

[Ray,IN]

Originally Posted by Doug427

Since I have fully fallen on my sword to the point of impaling myself on it in admitting my ignorance in all this, I'll ask another question that is probably very obvious to all of you but not to me.My engine brake (Jake?) is a two setting affair - high and low. How does one determine which setting to use? I know nothing of this device called Jake.


By way of explanation, this is my first RV. I have never driven a large diesel vehicle before. I spent the first 50 years of my life on Long Island, NY where it's as flat as a pool table. I then moved to Houston for the last 11 years, where again, it's as flat as a pool table. That's my story and I'm sticking to it.


I figure it's better to sit here safely at home working this all out thanks to your expertise and generosity helping out the new guy, then bombing down a mountain out of control wishing that I had asked.

According to the sales brochure;

it has an engine brake for the ISL Cummins engine, and is much more effective than an exhaust brake. An engine brake alters the valve timing and somewhat turns the compression backwards, which makes the engine retard the drivetrain instead of propel the drivetrain.

[richard5933]

Originally Posted by Doug427

...My engine brake (Jake?) is a two setting affair - high and low. How does one determine which setting to use? I know nothing of this device called Jake. ..

It's not as complicated as it might seem and depends largely on how steep the grade is. As you are going down the grade, put the engine brake on high if you think it's a steep grade and on low if you think it's not too steep. If you're not sure, then start with high. You'll know soon if it's too much engine braking as you'll slow down more than you want.

If you are on the low setting and the coach keeps gaining speed just coasting down the grade, switch to high.

Ideally, the engine brake should be holding you at the desired speed as you descend. On really steep grades you may have to use the service brake occasionally, and in those situations do something called "stab braking" (Google it or watch some videos). This intermittent braking allows the service brakes to cool between applications. Riding the brake all the way down the grade is a good way to start a fire in your brakes or lose your brakes.

[shoalsgary]

Originally Posted by rarebear.nm

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.

I HAVE noticed that Allisons WILL let the engine lug more often than not.

[arcaguy]

There's really not much to add here, most of it has been covered several times. I will just add something I once heard about pilots that applies equally to RV drivers: "There are old pilots and there are bold pilots, there are no old bold pilots." Safe travels and don't ride the brakes.

[MN_Traveler]

I guess I am lucky in that I don’t have any engine/ trans / exhaust temperature issues. Oh, I watch them ... but they just never get out of control to the point where I need to take action. But then again, I focus on keeping speed under control, so maybe the temps just follow? Maybe newer technology (2012). I will say that the engine temp can climb, but then something in the system kicks in and quickly pulls the temperature down - then the cycle repeats. I don’t know what it is that is kicking in - maybe someone here does? (ISB, Allison trans)

[Crasher]

Originally Posted by MN_Traveler

). I will say that the engine temp can climb, but then something in the system kicks in and quickly pulls the temperature down - then the cycle repeats. I don’t know what it is that is kicking in - maybe someone here does? (ISB, Allison trans)

You have a 2 stage fan. When my engine temp gets up to 210 on a long assent, the fan clutch locks up turning the fan faster till the temp falls back to approximately 185 when the clutch releases. If needed, the process repeats itself.

[Crasher]

Originally Posted by Doug427

Since I have fully fallen on my sword to the point of impaling myself on it in admitting my ignorance in all this, I'll ask another question that is probably very obvious to all of you but not to me.My engine brake (Jake?) is a two setting affair - high and low. How does one determine which setting to use? I know nothing of this device called Jake.


By way of explanation, this is my first RV. I have never driven a large diesel vehicle before. I spent the first 50 years of my life on Long Island, NY where it's as flat as a pool table. I then moved to Houston for the last 11 years, where again, it's as flat as a pool table. That's my story and I'm sticking to it.


I figure it's better to sit here safely at home working this all out thanks to your expertise and generosity helping out the new guy, then bombing down a mountain out of control wishing that I had asked.

You have had a lot of advice given as I predicted earlier. Not having any experience driving a big heavy vehicle, you have a big learning curve ahead of you. Take it one small step at a time. My advice is to stay away from the mountains till you feel comfortable driving, slowing and braking your new coach on level roads. Next learn what happens in small hills. Learn how much force it takes to stop it when descending a small to moderate hill. This will give you an indication what it will be like when the downhill is several miles long. Don't wait till you're topping your first mountain pass to learn these things or you might not get a second chance. Experiment with the HI and Lo of the Jake brake. Learn how to slow down without the foot brake. The Allison and Jake brake are your best friends when descending a long 6-7% mountain grade. Most RV owners have been where you are now. Common sense and caution should be on your mind as soon as you start the engine.

Good Luck and be Safe.