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Old 12-20-2008, 05:46 AM   #1
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G'morning ALL: Well, guess I'll finally swallow my pride and ask a question about driving our MH that I should already know....but don't know for sure!! After having bounced around since 2005, it's kinda embarrassing to ask this now, but it's something I've wondered about off and on and since it's kinda a quiet time on this forum, I figured now might be the time. Here goes...... What is the correct way to use your transmission, engine brake, cruise control and accelerator when traveling in parts of the country having extreme ascents and descents as in the mountains of the West (ie., Loveland Pass, Vail Pass, Wolf Creek Pass, Beartooth Pass, etc.). I know it'll depend on the rig being driven (our current coach is an 08 Essex, 45', 6 speed Allison Transmission, Hi/Off/Lo Engine Brake toggle, 500 HP Cummings ISM, and is just under weight when loaded and towing an UGLY Honda Element toad). For example, this last summer we were heading East on Hwy. #160 from Durango, CO, and ofcourse had to climb over the 10,850 ft. Wolf Creek Pass East of Pagosa Springs. (Yup, I've heard the song and LOVE IT)! Anyhow, we made it to the top, stopped awhile at the turnout, and continued East down to overnight at Alamosa. The thing is, I crossed this pass using same tranny set up as I do anywhere else and no, I've NEVER driven the rig in ANY other (downshifted) position but have wondered if I was supposed to. When hittin the road each travel day, we start her up, disengage parking brake, push the 'D' button on the transmission selector and off we go. In this instance, as we neared the upper reaches of Wolf Creek Pass, I had the accelerator almost on the floor, and we S L O W L Y pulled on up to the top of the pass at maybe 25 - 30 mph and no more, with the tranny readout having downshifted (automatically) to 6/3 or 6/2 but she was REALLY PULLING to maintain speed. Aside from detaching the toad and driving it over the pass (or is THAT the correct thing to do), should I have changed "MODE" and/or used the down/up arrows on the selector to change gears in some other manner than simply leaving it in 'D' and letting the engine power, torque, and automatic transmission handle the ascent??? Can any of you BIG RIG JOCKEYS set me straight on the best way to haul over some of these steep routes. Thanks. Steve & Lynette
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Old 12-20-2008, 06:11 AM   #2
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About the only thing I may have done differently, not sure because the only thing you left out was the engine RPM when you were pulling the pass at 25 or 30 MPH, would be, with cruse control off, to shift the trans down to highest gear where you could still maintain a constant speed with the engine rpm's at or above the peak torque curve. This will keep you from lugging the engine, keep the cooling system temp down and generaly get the best fuel mileage. (yes maybe 2MPG climbing the pass) As for down hill if you got down using the engine brake only, no service brakes, you did it exactly right.
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Old 12-20-2008, 06:28 AM   #3
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I am by no means an expert. I have driven diesel pushers since 1995. I have not had a Jake brake only exhaust brake units. On long uphill grades I want to keep the RPM up usually around 16-1700 so I manually downshift from 6 to 5 to 4 as the RPM drops toward the shift speed %0 for 5 and 42 for 4. So far this has worked and on a 7-8% grade I usually top out doing 35 - 40 MPH. This has worked on Cuesta grade near San Luis Obispo Ca, Tehachpi Pass, the grade on I15 from San bernadino toward Barstow, Etc. Going down I again use 4 or 5 again watching the tach such that I do not exceed 2300 RPM using the service brake to slow down as that level is reached...pumping the service brake vice a steady foot pressure until the speed is reduced and RPM is around 1800.
On one occaision when I lost the Pac brake I used 2nd and 3rd to descend a 5 mile 7% grade in British Columbia.
Watch the RPM and avoid service brake overheating.

Ronnie
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Old 12-20-2008, 06:51 AM   #4
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Steve - I'm pretty sure your Essex has the same transmission as our KGDB. It's the 4000MH I think. If the readout was showing 6/3 or 6/2, it was shifting correctly on it's own. The first number is the "desired" (or max) gear, the second is the actual. You can change the desired gear with the buttons, but the tranny is going to pick it's own preferred gear lower than that, if needed.

joe
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Old 12-20-2008, 07:04 AM   #5
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Here's an article regarding steep hill driving if you have not already read it. LINK

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Old 12-20-2008, 07:26 AM   #6
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lug's article is spot on. Especially the wet/slippery road stuff!!!!

I run an EX with toad all over CO on even worse grades like you do and basically, I let the K2 do all the work. The EX/K2 drive systems are extremely sophisticated and may not apply to other rigs. 95% of the time I leave the cruise ON both up and down. I find the engine brake is smoother and far more controlled leaving cruise ON going downhill. UP it'll be at WOT (wide open throttle - not that a diesel has a throttle) on cruise or your foot, so let the cruise hold it for you. The only thing I change is the hi/lo setting based on the descent grade. Generally, if less than 5% leave it in LO and if greater than 6% leave it in HI. Those common 6% grades will vary - wish we had a med setting! The engine brake setup is designed to do most of the work. If necessary, to use the foot brake DO NOT RIDE them, firmly slow down to 5-10 below desired speed and release. Around town leave it OFF. On occasion I'll nail the foot brake hard on a good downhill to really heat them up.

The CRITICAL judgment on your part is to decide on what speed to descend at as you top the hill and lock on that speed at the top, not after. As you know, the K2 cruise will allow an additional 5-10mph higher than setting before brake activation, so take that into account as well.

Let the K2 do all your work for you... It's more than able to.

PS I have NEVER encountered a situation that required me to manually downshift (UP hill or DOWN hill) at any time. Frankly, I'll be so bold to say you should never "have" to. Certainly, I do play around manually shifting but that's it. The engine RPMs have been correctly maintained by the cruise/brake every time. If I see the RPMs getting high while on engine brake, that's when I'll foot brake a little - but the reason they get high is that I misjudged and descended too fast. I can't ever recall having the engine lug uphill (low RPMs) while on cruise either.
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Old 12-20-2008, 12:04 PM   #7
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Only time I've purposely downshifted was to prevent overheating. On the highway up to Mt. Charleston just west of Las Vegas, it's a looooong fairly steep grade. With my previous coach, Winnebago with a 350CAT and Alisson 3000, the heat started getting a little higher than what I wanted to see. The optimum cooling RPM for DP's is around 2200 RPM. So I took it out of cruise, forgot about the speed, downshifted until I found a gear the engine would pull at 2200 RPM and then used the foot throttle to maintain that 2200 RPM. Engine cooled right down and it motored up the hill like nobody's business. Other than that, which is the rare occasion, I've never had to mess with the gears, just D and go (including Wolf Creek Pass, which that same Winnebago went over just fine).
Alan
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Old 12-21-2008, 04:18 AM   #8
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HEY!! THANKS TO ALL OF YOU!!! Wonderful info for something I've never been real confident that I understood well. I've just got to learn to pay more attention to those RPM points. You guys are GREAT!! Steve
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Old 12-23-2008, 09:01 PM   #9
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RVDude, I swore my owners manaul said the jake brake will not engage with the cruise control on? I have never tried it, but I would never have let it get 10 mph over the set cruise speed either. I tend to be very careful coming down, I've seen my share of runaways and fried brake systems.
I have always just killed the cruise and switched between high & low jake to keep my downhill speed in line.
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Old 12-24-2008, 04:34 AM   #10
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On my DSDP, the Jake Brake engages at 5 MPH over the Cruise Control set speed.

I do turn the cruise off on steep down grades and use the Jake Brake to keep my speed where I feel comfortable.

Like John, I'm very careful coming down steep grades.
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Old 12-24-2008, 05:11 AM   #11
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Route 66:
On my DSDP, the Jake Brake engages at 5 MPH over the Cruise Control set speed.
</div></BLOCKQUOTE>

I wonder if I can get Newmar or Spartan to adjust the cruise on my KGDB to engage the Jake at 5mph over? I think it's set to 10 now, and that's too much for my taste.

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Old 12-24-2008, 05:18 AM   #12
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I would think Spartan/Cummins/Newmar could do it. Any of them with the ability to get into the software of the rig.
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Old 12-24-2008, 05:27 AM   #13
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Ditto Dirk. They should be able to adjust that no problem.

5 over seems about right. You might even consider 3 mph.
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Old 12-24-2008, 05:30 AM   #14
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CSX - On my EX, the ENGINE brake (I don't think it is a Jacobs Vehicle Systems, Inc system, hence it's not really a Jake Brake) positively engages under cruise in every situation even if the hi/lo switch is off - but it engages 5-10mph OVER set cruise speed. If the hi/lo switch is on, it will respect the switch setting. I have found that the cruise can apply and maintain the engine brake action far smoother than I can manually. Hence, as I crest a hill I'll reset the cruise to about 5 less than my desired descent speed set the hi/lo based on slope (lo=&lt;6% hi=&gt;6%) and just enjoy the ride.
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