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Old 09-05-2018, 09:31 PM   #43
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Originally Posted by A Traveler View Post
Wow.

That is some of the absolute WORST advice I have ever seen posted here! PLEASE don’t drive like this!

It is so bad that I don’t know where to start in trying to explain why it’s bad advice. So I won’t...

WOW IS RIGHT!!! Professional Oversize lowbed driver for over 40 years 130,000 plus pound loads and I LOVE to read this stuff.
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Old 09-05-2018, 10:32 PM   #44
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"Cruise will keep a steady amount of power or braking at your set speed"
Cruise control does auto braking? Not in many vehicles.
Some engine braking (no accel applied = engine braking) but not wheel braking.
But I get and mostly agree with your larger point.


Sorry, I was out of line. I assumed jake brakes were standard issue. With an engine brake going downhill is much less of a concern.
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Old 09-05-2018, 10:42 PM   #45
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With all due respect, I strongly disagree. When climbing steep hills, manually selecting a lower gear permit me to run my C12 in the 1800-2000 rpm range which improves engine cooling and keeps the engine at roughly peak HP.



Coming down a mountain, manual gear selection allows me to keep the rpm's close to engine red-line which significantly increases the braking HP of the Jake Brake.



In contrast, the Allison, even without cruise control engaged, will repeatedly attempt to upshift to 5th (even 6th) going uphill which forces the engine to run in the~1200-1400 rpm range which results in it getting significantly hotter. Going downhill, my transmission is set to automatically shift to 4th when the Jake is applied, but going down some of the steepest hills this summer I've put it into 3rd a couple of times.


I bought my Coach with 17k miles, now have 84k. I have never touched the manual shift buttons. I’ve climbed west out of Denver a half dozen times, SW to/from Vegas a few times and also in and out of Jackson Hole west bound with that crazy hill. East and west on hwy 3 in southern BC. The engine and tranny have never needed my help other than to make sure the brake is set to 3rd. The Coach weighs in at 52k. None issue. Sometimes pull a trailer with a car. Most often no tow. I don’t ever try to manage rpm.
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Old 09-05-2018, 11:22 PM   #46
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Sounds like you have a great transmission.
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Old 09-06-2018, 12:03 AM   #47
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After reading thru all these posts, I gather most here are driving newer (less than 10 years old) rigs that have electronically controlled engines.
We drive a 1998, 42’ DP with a 350hp Cummins 8.3l/Allison combo. Completely mechanical - no fancy electronics to “help” it along.
Been on the road for the last 5 years. Still finding better and better ways to control the engine when climbing.
I manually shift a lot. Drop a gear and run 5th gear at 55-60mph driving.
I have to keep my eye on the boost/exhaust temp/engine temp at all times when climbing hills. Max boost is 19, rpm’s need to be between 2050 and 2350. This allows me the best torque/speed and temp. If I over boost, the exhaust temp rises and so does the engine temp. Boost and piro gages were relocated for easier viewing.
We have successfully several passes out west, with the air temps in the high 90’s. Practice and patience have let us travel wherever with minimal issues. We toad, also.
If I allowed the tranny to shift on it own, we would overheat at almost every steep grade. Just not set up that way. Wants to stay in higher gears too long.
Everyone has to find out how THEIR rig needs to be driven. They are all different.
Just my 2C.
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Old 09-06-2018, 12:04 AM   #48
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I bought my Coach with 17k miles, now have 84k. I have never touched the manual shift buttons.
With my C12 and Allison 4000 transmission I don't "have" to shift manually when going up and down hills but I feel there is a performance improvement by doing so. Going up steep grades, by shifting to 4th I can climb at max HP and prevent the transmission from "hunting" between 4th and 5th gears. For my MH that means that engine temp doesn't rise above ~197 on even the steepest grades and the transmission stays <194 because it's not shifting back and forth.

I like to descend steep grades in 4th (or 3rd if they're very steep). By staying in 4th my Jake comes on and off as I use the accelerator without causing the "jolt" of a downshift. I can descend a 6-8% grade in 3rd pretty much without using anything other than the Jake.

I'm not trying to convince you to change your approach to driving; I'm just providing the rationale for why some of us choose a different approach.
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Old 09-06-2018, 08:12 AM   #49
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Touching the transmission or not may have a lot to o with how the transmission is tuned to the weight of the coach. The shift points are one size fits all, which is in the ball park, but not correct for every coach. Because I installed the transmission in my previous coach, I programmed the shift points vs load characteristics. As a result, the trans was tuned to the weight of my coach, the horsepower, and my driving style. I had a manual push button shifter, but never used it. I did have a performance button that I occasionally used, but never used the push buttons. So I believe manually shifting is just compensating for the weight differences of some coaches.
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Old 09-06-2018, 09:05 AM   #50
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Echoing what some others have said - i have adopted a simple rule: if i need to use my brakes to avoid speeding up while going down, i am going too fast. First try: downshift. If that does not slow me, turn on engine brake (mine is only single stage). If i still speed up, turn off engine brake, downshift one and apply service brake until the transmission actually downshifts. If still speed up, apply engine brake, etc, etc. pretty quickly i find the right combination for that grade. Sometimes i just toggle the engine brake on and off to keep within a range of 5 mph or so. Sometimes this translates into 60 mph or so (rolling grades in eastern NM, sometimes 25 mph or so (I70 eastbound into Denver). My bottom line is to find a place where i DONT need to use my brakes.

(Aside: an earlier poster mentioned Wolf Creek Pass. Many years ago i bicycled that baby, and at the time wondered what it would be like to drive it. Very steep grade and some crazy hairpin turns with very high drop offs! Someday i really need to take the DP over that road!
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Old 09-06-2018, 03:49 PM   #51
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That never made sense to me. Up hill grade is 6%, down hill is 3%. I will be in a different gear.

J
Me too
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Old 09-06-2018, 04:09 PM   #52
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FLavionics, the Cummins ISB was originally designed as a joint venture by Cummins and Case as a tractor/backhoe engine. Later it was also adapted to the Dodge pickup line. It is a great engine as long as you keep the gross weight down. Unfortunately, some motorhome manufacturers have installed it in coaches over 30,000#. It will function okay, but it will not win any awards for high speed up hills or mountain grades especially in hot weather.

Try to keep your gross weight down if traveling into mountainous areas and enjoy the scenery.
Best of luck!
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Old 09-06-2018, 06:59 PM   #53
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So my new to me DP is rated 360HP @ 2400RPM
and 800 ft-lbs @ 1800RPM.

When climbing a mountain would it be best to stay at maximum torque by manually shifting which would be 1800RPM?

And what about descending
First if you in fact have a 6.7 Cummins(great engine) an coach weing3200lb an perhaps a toad you will struggle going up a 6 or 7 % grade.As others said manually keep engine at 2000 rpm .Shift down when engine is pulled down to perhaps 1800 you will get to top. Experience will let you know when shift will be done smooth
Now for serious thing . At most serious grades there will be a pull off an mandiatry for large trucks to pull off==== YOU PULL OVER Also read the signs posted-most allow 20mph maximun down grade. You rv an with a toad is very heavy. As you again start down hill that might have more steepness or less follow a tractor trailer who stays in right lane holding 20 mph.If you have a exhaust brake only use gear that will hold pposted speed In my trucking days i never lost brakes but on hills farming i have an when sudenly there are no brakes it is not a pleasant thing.But alweys start slow down long steep grades an you will never get in a situation where you might end up in a truck runoff ramp or worse.
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Old 09-06-2018, 07:56 PM   #54
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"hrw" may not be wrong. Take a look at his coach. It's a high end coach with a huge motor. If everyone had that motor, there wouldn't be much discussion. It has the HP to pull big grades.

For everyone else, many are trying to pull grades with engines that are great on flat land, but not so stellar in the mountains. The REALITY.....the smaller the engine, the more work you'll have to do to climb a grade without sitting between two semis doing 35 mph.
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Old 09-06-2018, 08:04 PM   #55
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Those of you who espouse just putting the transmission in “D” and engaging cruise control don’t understand that this method is fatally flawed. If you use your cruise control in mountainous territory and start up a grade, your coach can only react to something that has already happened. It cannot anticipate anything. Driving this way gets the engine behind the power curve, lugging uphill at low rpm and high boost pressures. By the time the transmission figures out that you’re going up a hill and shifts down a gear, it’s too late.

By ANTICIPATING the grade you see ahead of you and getting into the right gear to get the engine at its HORSEPOWER peak BEFORE you get into the grade sets you up for a much easier climb...easier on you and your engine.

These big coaches are not cars. You CANNOT just put them in “D” and drive.
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Old 09-06-2018, 08:10 PM   #56
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"hrw" may not be wrong. Take a look at his coach. It's a high end coach with a huge motor. If everyone had that motor, there wouldn't be much discussion. It has the HP to pull big grades.
Given that he states that his coach weighs in at 52,000 lbs, my HP to weight ratio is equal to or better than his. Yes, his engine is large enough to make it possible to drive the way he wants. It doesn't mean that his choice is the most sensible, even if he has the HP to do it.

For example, I can do drive exactly as he describes and my engine temp going up a steep mountain pass at ~50-55 mph will be in the ~203-205 range by the time I reach the top. OTOH, if I gear down and keep my revs up I can keep the temp in the 195-197 range while still climbing the hill at the same speed.

I'm not saying that the modest reduction in temperature is a big deal, but keeping the engine and transmission as cool as possible seems, to me, to be a sensible approach.
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