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jkoeni01

Mountain driving

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I will be driving I-75 in Tennessee where there is reported to be a 4 mile climb and then a 4 mile descent at a 6-7% grade. My rig is a Newmar Kountry Star with a 330 hp diesel engine. I will be towing my 3000 lb subaru. I've also come across discussions regarding transmission heat but never found any good explanation of how I tell when there might be a problem brewing.

Any suggestions on gear selection for the climb and, more importantly the descent. I've never driven in the mountains with an RV and definitely not anything this size.

Thanks for any recommendations.

Jkoeni01

2005 KSDP 3910

Toad 2003 Subaru Legacy

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With your Allison 3000 transmission, heat under climbing conditions should NOT be an issue. The torque converter is LOCKED in 2,3,4,5 and 6th gear. It is slippage in the torque converter that produces most transmission heat. In fact about the only time the Allison will heat up is in stop and go traffic where the torque converter IS slipping. So if stopped at a long light, etc, put it in Neutral.

As far as gear to climb, your Cummins (same for Caterpillar and 4 stroke Detroit Diesels) can most economically climb at any RPM at or above PEAK TORQUE RPM. So, Wide Open Throttle as anything over peak torque RPM is fine-- all day long.

The only reasons to higher RPM:

1. A (little) more speed.

2. If coolant temperature begins to rise, higher RPM spins the water pump faster/circulates more water to the radiator. Note: particularly on rear radiator configurations, the FRONT of the after-cooler (look inside the fan shroud/between fan blades) needs to be cleaned at least annually to keep the cooling system working properly.

And gear for descent (with exhaust brake ON) is "the gear that holds your speed in equilibrium-- so you are neither speeding up nor slowing down. That speed/gear may be 15 mph or 60 mph depending on the grade. Physics dictates that your equilibrium speed will be somewhere between that of a loaded 18 wheeler (you will be faster) and and empty one (you will be slower). And even if on a perfectly straight road and 7% grade, your equilibrium speed will be SLOW-- well below how fast you could "take the curves".

Brett Wolfe

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One more tip for driving in mountains with a motor home. Truck drivers will tell you that it is better to use your pedal brakes periodically to slow the motor home significantly rather than using the brake pedal continuously. Continuous use of the pedal brakes will heat them up to the point where they become ineffective. If you notice the RV speeding up as you descend, let the speed increase for a little while then use the brakes to bring the speed back down. When the speed is back down, release the brakes and let the engine brake work while the pedal brakes cool down. If you learn the RPM shift points for your transmission, you can effectively prevent the transmission from up shifting as your speed increases. I know for instance that when our transmission approaches 2500 RPM it is reaching a shift point. At that point I will apply the pedal brakes to bring engine RPM back down to about 2000 and then release the foot brakes.

One of the keys to having the engine brake do most of the work (most desirable) is to top the mountain grade at a slow speed and engage the engine brake before speed begins to build up on the down slope. If you are facing a long down grade at 6% you will likely want to be in third gear, not fourth gear. Some people seem to be comfortable on these down grades at 60 mph. I wouldn't be able to stop the RV at that speed if I came around a curve to find stopped traffic or an accident and don't want to be going faster than I can quickly bring the RV to a stop. I usually have truckers (real pros) passing me on down grades, they must be empty or hauling potato chips! The really loaded trucks will be traveling about the same speed I am traveling. When I see the heavily loaded truckers starting to accelerate I know the bottom of the grade is near and then I'll let the transmission upshift.

You will get the hang of it as you travel, it really isn't difficult to do and nothing to be feared if you take time to learn the basics as you are doing here. Consider this trip as a beginners course for some travel in the west! Enjoy!

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I agree with Tom on HOW to use the service brakes (brake pedal) if it is needed on a descent.

BUT (read that a large BUT), if you continue to need to use the service brakes to keep your speed in equilibrium, use the service brakes long/hard enough to slow you down enough TO GRAB A LOWER GEAR that WILL keep your speed in equilibrium.

Basics are that service brakes are for stopping ONLY, not for controlling speed of descent on long grades.

Brett Wolfe

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Hi Jim,

I hope your still reading this thread. Sorry to be a bit late in posting a reply. We just got back from the Newmar Kountry Klub Florida State Rally.

My coach is the same as your coach. The transmission should NOT be in economy mode. Leave it in the default power mode. On the up hill, let Allison decide what gear it should be in. As you reach the top of the hill/mountain, turn on the engine brake. On I75 that should be enough for you to comfortably descend. If you continue to gain speed, stab the service brake (brake pedal) hard to slow the coach. When you release the service brake, manually downshift the Allison one gear. If you need to stab the brakes again, once you release the brake pedal, manually downshift the Allison one more gear. Repeat until you are comfortable with the speed the coach is holding. On I75, I have never needed to do this, but you may want to try it. This way if you need to do it someday, you'll be comfortable with the process. Once at the bottom of the hill/mountain manually up shift the Allison back to 6th gear.

I tow a 5.2K lb GMC ENVOY. My combined weight is a bit more than your weight at 34K+ lbs. I've had to use the manual downshifting of the Allison only with grades much steeper than 6%.

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Gary,

As you suggest, there are certainly different (equally acceptable) techniques for climbing a grade. It really boils down to how much driver interaction one wants as well as how robust the engine cooling system is.

I prefer to use economy mode and use the down/up arrows to TELL the transmission what I want done. It is equally acceptable to leave it in either economy or power mode and let the Allison "do its thing".

I think we both agree, but want to make VERY clear about one point.

You said, "Repeat until you are comfortable with the speed the coach is holding." For those new to driving heavy vehicles, we need to point out that the "comfortable speed" has little to do with how straight or curvy the road is, and EVERYTHING to do with holding the vehicle's speed in EQUILIBRIUM. You will see just as many truck runaway lanes on straight descents as on curvy ones! Once a heavy vehicle's speed gets too much over equilibrium speed, the brakes are truly inadequate to "regain control".

This is something everyone operating a heavy vehicle has learned-- you need to know how to use your exhaust brake/Allison transmission along with perhaps an OCCASIONAL use of the service brakes to safely descend a grade.

If in doubt start slower-- it is always easier to speed up. And watch the 18 wheelers. You should be faster than the loaded ones and slower than the empty ones.

Once you get the hang of it, you can use ALL these things to control speed:

Exhaust brake on/off

Up/down arrows to lock the transmission in a gear

Service brakes.

Example: You are on a grade where 4th gear with the exhaust brake on provides too much braking. But turning it off/touching the throttle allows not only the brake to turn off, but the transmission to up-shift, causing you to accelerate. Here you may want to use the down arrow to "lock" the transmission in 4 gear and merely toggle the brake switch on/off to fine tune your speed.

Brett Wolfe

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Hi Brett,

Since the author's coach and mine are the same and I am familiar with the road mentioned in his OP, the process I use was suggested for a couple of reasons.

1. On the uphill climb, my ISC will have an increase in temp. On long climbs, in the summer, it will get to about 220 degrees F. My cure to keep the temp around 200 degrees F is to ensure Allison will downshift quickly to keep the RPMs up. In hill climbing I have experimented with economy mode and was not pleased with the engine temp. The default mode solved the problem, without further intervention by me.

2. On the downhill, I want Allison to choose a lower gear as soon as possible. Turning on the engine brake at the top of the hill tells Allison to start the search for 2nd gear. This may make the choice of power vs. economy mode a moot point. However, I have not been as pleased with the economy mode on during a decent. Therefore, I have found, with this coach setup, the engine brake on and economy mode off, very little of my intervention is required.

You hit on the right thought that those who like to personally be involved with the choice of gears, may not like my process. I am not one of these drivers. Once I understand my coach, I prefer to set it up according to past successful experiences and let the components do their job. I am very aware of grades that will require me to adjust Allison's choice of gear. I've done it many times.

The OP is about I75 in a certain area, with a certain coach, engine and transmission combination. I am very familiar with this road and coach component combination. My post was not general information on how to climb/descend mountains. It was specific to the author's OP situation.

With this coach setup, I use economy mode very little. The coach setup has turned out to be very stable. Allison rarely (almost never) downshifts on small hills, overpasses and bridges. It may be more useful in other coach combinations.

All the above is after 46K miles, with this coach, in all kinds of driving conditions.

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As a newbee to driving a large rig I've searched blogs, asked the manufacturer, and posted here. The information gained in this blog was truely the most helpful. Our descent was so simple and easy. I just turned on the engine break. My wife, who was petrified at the notion of losing control down a hill was surprised at our return to Michigan when she was driving north near Cincinnatti. She woke me up frightened and said, Jim what do I do, I'm at the top of this big hill. I told her what to do and she smiled all the way down the hill.

Thanks again for the support and ALL the advice you folks have shared. I hope I can help others as much as time passes.

Jim

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I am new to Motor coaching. I have the same question about driving in the mountains near yellowstone. I have a gas burner ford v-10. Any suggestions on handleing the mountains out there? Thank you,

Travis

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Travis,

Welcome to the FMCA Forum.

The same principals apply to ALL heavy vehicles-- gas, diesel, 18 wheeler, RV.

When descending use a low enough gear (even first) such at your speed is in equilibrium-- you are not speeding up or slowing down. You do NOT want to use your brake pedal to control speed,-- use it ONLY to slow you down enough to "grab a lower gear". Your equilibrium speed will be faster than a loaded 18 wheeler and slower than an empty one== straight physics.

Until you get the hang of how to control your vehicle's speed, play it conservative. Sure easier to up-shift a gear than to have to use those truck run-away lanes!

Climbing, keep an eye on engine temperature. Run RPM's at or above peak TORQUE RPM for your engine but below peak HP RPM for reasonable performance without excessive fuel consumption.

ENJOY YOUR TRIP. 100% of us had a "first trip in the mountains"!

Brett Wolfe

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Travis,

A TOTALLY separate issue is making sure your RV is in mechanically top condition, as mountain driving IS more stressful on machinery.

On your gas coach:

1. Change brake fluid if over 2 years old in humid area or 3 in desert climate. Brake fluid is supposed to absorb moisture to keep brake components from rusting. As it does, fluid boiling point goes from just under 500 degrees F to 286 degrees F. BIG DIFFERENCE.

2. If the coach has not been used much and has floating caliper brakes, clean AND LUBE THE SLIDE PINS. These can rust in place and cause major problems.

3. Same as most vehicles-- air and fuel filter, spark plugs if they are due to be changed, etc.

4. Correct tire pressure. Determine correct PSI from YOUR ACTUAL WHEEL POSITION OR AXLE WEIGHTS.

5. Check suspension components for wear-- shocks, sway bar bushings, bell crank (P30, not Ford), etc.

It is sure easier to discover and fix problems BEFORE you leave home than on the side of the road.

Please ask questions so we can help you with the "Learning Curve".

Brett Wolfe

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One point that I may have missed in the above posts. Allison says that when climbing steep or long grades, keep an eye on the transmission temp gague. If the tranny goes over 220 deg. shif down one gear to bring up the RPM and better cool the transmission.

Thanks to everyone for the helpful posts. I too am still learning but my first "mountain trip" was the cabbage patch in Ore.

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One point that I may have missed in the above posts. Allison says that when climbing steep or long grades, keep an eye on the transmission temp gauge. If the tranny goes over 220 deg. shift down one gear to bring up the RPM and better cool the transmission.

Thanks to everyone for the helpful posts. I too am still learning but my first "mountain trip" was the cabbage patch in Ore.

Your Allison transmission should not overheat while climbing unless you allow the transmission to "hunt". Hunting is the repeated shifting back and forth between two gears because you can not pull the grade in the higher gear, but the next lower one is low enough to allow you to accelerate to where it up-shifts-- process repeated over and over.

Because the torque converter is locked in the Allison transmission, there is no slippage which is the prime cause of heat in some transmissions (particularly older ones without lock-up converters).

Yes, transmission temp will go up a little, as the transmission cooler on the vast majority of coaches is in the radiator. So when engine temp goes up a little, so does transmission temp.

And the advice is good-- if temps rise, use the "down arrow" to select a lower gear to raise engine RPM's and back off the throttle. But normally you will notice a rise in engine temperature long before a rise in transmission temperature.

BTW, to keep the transmission from hunting, you also use the "down arrow" to lock the transmission in the lower gear. When the grade eases to allow use of a higher gear, just hit the "up arrow" or "D".

And feel free to use the up and down arrows and "mode" as much as you want. You can NOT harm the transmission. Even hitting the down arrow 4 times at 65 MPH will do no harm-- in fact, that is EXACTLY what happens when you hit the exhaust brake if you have a 2nd gear pre-select. The transmisson ECU KNOWS that the command is to "downshift one gear at a time in such a way that engine RPM's are kept in a pre-determined safe range until the pre-selected gear is reached".

Leaving the transmission in economy mode and using the up and down arrows gives you all the control of a manual transmission (only without a clutch). Do you need to do this, NO. But you CAN do it to more precisely control the transmission. After all, the transmission is REactive, seeing what happened well behind you. You can be PROactive, seeing ahead of you that you are about to top a grade or begin up a 7% grade.

Glad you enjoyed your first trip in the mountains.

Brett Wolfe

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Guest Wayne77590

I have used Brett's technique on more than one occasion, and it works very well. The Missouri hills are wonderful to ride and, in economy mode, I used the down arrow to keep the transmission in the proper gear to maintain my speed. The key was to have the vehicle going slow enough to shift to that gear. On an occasion where I was going faster than the gear selection I wanted would allow, I press firmly on the service brakes, and within 3-5 seconds I was at a speed that would downshift and from that point on kept my speed where I wanted it.

Lot's of good advice in the forum.

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I live in the western part of Tennessee, the flat part. We decided to make a trip to the mountains and I remembered the hills on I-40 coming off the plateau. I was really anxious about going down these long steep hills pulling a Saturn behind. I made it fine going up with a 300 Cummings and Allison transmission but the thought of going down the long steep hill was still a major concern. Please don't do this but I got in the left lanes, that's where the run away lanes are and started real slow, the exhaust brake worked great and I really did not have to use my service brake much, I even got over to the right lane and acted like an experienced RV'er.

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Montie,

The secret for first-timers is to start slow in lower gears (use Allison down arrow). Lots easier to speed up (up arrow and lightly touch throttle for 2 seconds so the transmission up-shifts and/or toggle off the engine brake momentarily) than it is to be going too fast and HAVE to slow down.

If speed starts to rise (you are above equilibrium speed=neither speeding up nor slowing down), use the service brakes to slow you down enough to down arrow to the next lower gear. You should be able to descend up to about an 8% grade (steeper than all but a handful of highway grades) BUT may be at 20 mph in 2nd gear. Obviously, the lighter your GCW and the more braking HP your engine has the steeper the grade you can take at higher speeds and still remain at equilibrium speed .

Never fear going too slow. The loaded 18 wheelers WILL POSITIVELY be slower than you and everyone in smaller vehicles who has ever driven in the mountains KNOWS that trucks descend SLOWLY.

Brett Wolfe

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Just a newbie question on this topic, I have a 6.6L duramax diesel with Allison 1000 transmission and exhaust brake. It makes me feel like the transmission is going to blow apart when the exhaust brake kicks in, any suggestions for a rig like mine compared to the "big boys" ??

Montie,

The secret for first-timers is to start slow in lower gears (use Allison down arrow). Lots easier to speed up (up arrow and lightly touch throttle for 2 seconds so the transmission up-shifts and/or toggle off the engine brake momentarily) than it is to be going too fast and HAVE to slow down.

If speed starts to rise (you are above equilibrium speed=neither speeding up nor slowing down), use the service brakes to slow you down enough to down arrow to the next lower gear. You should be able to descend up to about an 8% grade (steeper than all but a handful of highway grades) BUT may be at 20 mph in 2nd gear. Obviously, the lighter your GCW and the more braking HP your engine has the steeper the grade you can take at higher speeds and still remain at equilibrium speed .

Never fear going too slow. The loaded 18 wheelers WILL POSITIVELY be slower than you and everyone in smaller vehicles who has ever driven in the mountains KNOWS that trucks descend SLOWLY.

Brett Wolfe

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I have a 2006 Gulfstream, Ford v-10 with a torqueshift transmission. Any tips on mountain driving or tips on how to shift the torque shift transmission to maintain speeds down hill.

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I have a 2006 Gulfstream, Ford v-10 with a torqueshift transmission. Any tips on mountain driving or tips on how to shift the torque shift transmission to maintain speeds down hill.

Thought you don't have an engine brake, like the diesels, the rest of the driving/gear selection is much the same.

You will choose a low enough gear that your speed stays in equilibrium on descent.

I would suggest that you look up and make note of max allowable engine RPM (same advice for ANY engine). With the Ford V!0, it is happy at much higher RPM's than earlier engines.

Basic formula-- if you have to use your service brakes to control speed, use the service brakes long enough to drop speed so you can downshift to a lower gear. If you start to slow down too much, shift up one gear.

In really serious mountains, consider disconnecting the toad and driving separately. Taking that load off the engine both climbing and descending helps.

Brett Wolfe

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I live here in Western Colorado, so any where I go I have to go over major mountain passes. Having driven trucks all my life in Colorado I had my allison pre-select changed from 2nd gear to 6th. This way I can control the gear selection on the e-brake with the RPM's of the engine. I agree with the posts brakeing solution of using hard brake to slow down and not use continuelly. If your not knowledgeable or have truck driving experience this may not be a good option for a newbi.

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Gary,

As you suggest, there are certainly different (equally acceptable) techniques for climbing a grade. It really boils down to how much driver interaction one wants as well as how robust the engine cooling system is.

I prefer to use economy mode and use the down/up arrows to TELL the transmission what I want done. It is equally acceptable to leave it in either economy or power mode and let the Allison "do its thing".

I think we both agree, but want to make VERY clear about one point.

You said, "Repeat until you are comfortable with the speed the coach is holding." For those new to driving heavy vehicles, we need to point out that the "comfortable speed" has little to do with how straight or curvy the road is, and EVERYTHING to do with holding the vehicle's speed in EQUILIBRIUM. You will see just as many truck runaway lanes on straight descents as on curvy ones! Once a heavy vehicle's speed gets too much over equilibrium speed, the brakes are truly inadequate to "regain control".

This is something everyone operating a heavy vehicle has learned-- you need to know how to use your exhaust brake/Allison transmission along with perhaps an OCCASIONAL use of the service brakes to safely descend a grade.

If in doubt start slower-- it is always easier to speed up. And watch the 18 wheelers. You should be faster than the loaded ones and slower than the empty ones.

Once you get the hang of it, you can use ALL these things to control speed:

Exhaust brake on/off

Up/down arrows to lock the transmission in a gear

Service brakes.

Example: You are on a grade where 4th gear with the exhaust brake on provides too much braking. But turning it off/touching the throttle allows not only the brake to turn off, but the transmission to up-shift, causing you to accelerate. Here you may want to use the down arrow to "lock" the transmission in 4 gear and merely toggle the brake switch on/off to fine tune your speed.

Brett Wolfe

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