Shifting Techniques

Topic: Shifting Techniques (Read 1256 times) previous topic - next topic

Shifting Techniques

August 11, 2021, 09:35:16 pm

I'm just curious about different folks ideas on shifting techniques. I had the opportunity a couple of weeks ago for my first trip since bringing this coach home. DFW to Hot Springs Arkansas. Mostly flat interstate. But once off the Interstate there were some stretches of highway that required some drivers input. In economy mode with the cruise control on I noticed it would allow the engine to pull several hundred rpm below peak torque before down shifting. I read in the Cummins manual there was a 30 second limit to full throttle operations below peak torque. So staying in economy mode I would manually downshift at 1400 rpm. Which the book states is peak torque for the ISM500. There were a few pulls that I just sat back and watched what happened. It pulled down to 1400 and slowly to 1300 and held that before cresting the grade. I'm guessing the cruise control will go to WOT to try and maintain speed selected. This is my first MH and my first BIG Diesel engine. So I'm learning as I go. I've already learned a valuable lesson trying to get it home from Nacogdoches. Making the turn onto I-20 north of Kilgore I stepped on the throttle to make the left across two oncoming lanes of traffic about a quarter of a mile away. Not a lot happened for what seemed an eternity but in reality maybe 5 to 10 seconds. My girlfriend said that made me a little nervous. I said you should have seen it from my seat. 😂
After about 15 minutes I finally broke the vacuum lock on the seat cushion. I realized then this thing is closer to flying a big jet than driving a light truck. It takes a lot of energy for things to happen and they happen slowly due to weight. I was thinking once I was on I-20. It reminded me of what a check airman told me when I checked out on the MD80. Don't ever let those Pratt&Whitneys catch you at flight idle with your pants down. They took about 15 seconds to go from flight idle to go around thrust. Anyway. My apologies if I put this in the wrong thread. I've lurked here for over a year before buying. So now having to learn where to post and not just read. Thank you all for making this such a wonderful resource.

Re: Shifting Techniques

Reply #1 – August 11, 2021, 10:07:34 pm

Think L1011. Kinda slow starting but will generally go faster than you should.
Scott

Re: Shifting Techniques

Reply #2 – August 11, 2021, 10:17:15 pm

When diving I use economy a lot but when climbing a grade if the coach starts to
loose speed I take it out of economy and the trans shifts down and I keep my speed.

Re: Shifting Techniques

Reply #3 – August 11, 2021, 10:50:26 pm

Climbing any grade, I keep the RPM up close to fuel cutoff and drop a gear if necessary to keep it there but watching temp as I climb dropping another gear if necessary to keep the temp down and the RPM high. Moderate downgrades or flat terrain, I keep the RPM as low as possible. But I have a 4 speed so it's about 1500 RPM in 4th at 60 mph. Wish I had the 6 speed 4060.

Watch density altitude as West Coast temps now make 8000 foot summits way higher than that and your fan, intercooler, radiator are less efficient. EGTs can really climb at full throttle at lower RPMs. Keeping RPMs up keeps the water pump and coolant circulating with better heat transfer. Turbo may not keep the boost up at altitude so you will experience a certain power loss. Temp gauge only measures it at the sensor not in the hottest coolant passages next to exhaust valves in the cylinder head.

I used to climb as quickly as possible to 10,000 pulling the props back a couple hundred about 30 seconds after rotating. At 10,000, I would pull the props way back to keep the burn low but speed up.

Pierce

Re: Shifting Techniques

Reply #4 – August 12, 2021, 10:21:39 am

There is no "this is the right way for everyone" to drive in mountains.

I grew up on manual transmission vehicles. In mountains, I drive a motorhome the same way.

Economy mode and frequent use of the Allison shift pad up and down arrows. I, not the Allison determine what is needed. Pure physics says the larger/heavier the vehicle, the more its momentum. What that means is that the drivetrain is only REactive-- sensing what happened well behind you. You can be PROactive-- styling engine and transmission choices to what is in front of you.

Very few of us use cruise in the mountains-- more difficult for the driver to know exactly what is happening.

Yes, some just put it in "D" and drive. But, not my style.

Re: Shifting Techniques

Reply #5 – August 12, 2021, 10:32:52 am

I think this is one of the most enjoyable parts of diving our Foretravel. You can feel the diesel either reacting to the terrain or you can help it by putting it where it wants to go before the electronics react.

Compared to a car's engine our diesel runs in a relatively small RPM band after getting up to speed (1200-2200). Ours seems happiest, when working on grades, between 1800-2200 RPM.

To keep it in this band downshifting is essential. As I see a grade approaching I'll downshift to 5th on our 6 speed, which at 65 takes the engine up into that range. Then if the grade is steep enuf I'll continue downshifting when I see RPM starting to drop. Never look at the Speedo...just the tach. Then at the crest I leave it in the gear that I was using just prior to the crest and carefully use retarder and service brakes in the way down and begin up shifting as the grade lessens.

BIG SIDE BENEFIT: No overheating.

Re: Shifting Techniques

Reply #6 – August 12, 2021, 04:15:11 pm

Peak HP is where it will pull the best. Peak TQ is going to give best mpg.

Anything will get you there faster than a MD80, well, mostly.

Re: Shifting Techniques

Reply #7 – August 12, 2021, 09:16:12 pm

I usually manage the transmission by manually shifting in the hills, and traffic. Keeps the trans from constantly hunting, and keep rpm in the 17-1800 range. That seems to keep the ISC happy.

Re: Shifting Techniques

Reply #8 – August 13, 2021, 08:05:58 am

Florida Randy is spot on with climbing/descending a steep grade. Keep RPM's up, temps down and engine will be a happy camper as well as the driver and passenger!

Re: Shifting Techniques

Reply #9 – August 13, 2021, 01:06:36 pm

Thanks for all the great advice/techniques. It looks like I have been a little slow in downshifting. I was waiting until the RPMs slowed to peak torque before downshifting. My thought process was at peak torque it's pulling as hard as it's going to. Anything below that your losing torque and horsepower. But like I said. My first big Diesel engine. Hence all the questions. I will start preemptively shifting sooner. I've actually been surprised at the grunt this engine has in 6th gear and the hills it would climb without losing RPM. But it was Arkansas. Big difference once I get to somewhere like Colorado. And I'm very lightly loaded. Being new the bays are pretty much empty as is the inside as well.

Re: Shifting Techniques

Reply #10 – August 13, 2021, 02:48:36 pm

Gears are your friend. When I said I just take out of economy mode that is just the
first thing I do. If I can maintain speed and the engine temperature is steady all is good.
When I was on the Island I was going up a grade and I notice the engine temp was 199
shifted down a gear and the temp dropped.

Re: Shifting Techniques

Reply #11 – August 15, 2021, 07:28:48 am

General question - When you say economy mode, does that mean leaving the tranny is 6? Or whatever your highest gear is? I noticed on the inaugural drive home there were a few hills that seemed anemic, I thought the tranny would shift automatically. Does it not upshift? Or are you taking a proactive approach and changing them earlier as Brett said?

Re: Shifting Techniques

Reply #12 – August 15, 2021, 08:51:18 am

You may have a button next to your shift pad that say economy mode. You just push that button.
That button stays lit or on until you turn off the engine. I think that button changes the transmission shift patterns.
I notice if I don't use it the transmission seems to shift more often.

Re: Shifting Techniques

Reply #13 – August 15, 2021, 09:16:23 am

Quote from: movingman – August 15, 2021, 07:28:48 am

General question - When you say economy mode, does that mean.........?

You will find the Forum search function (top right corner of this page) is very handy for answering a lot of your questions. Searching the term "economy mode" or "mode button" will bring up many threads on the subject. Here are a few to get you started:

"Mode" button on Allison (Reply #3)

Got my Allison "Mode On"

ALLISON TRANSMISSION MODE BUTTON

Re: Shifting Techniques

Reply #14 – November 04, 2021, 02:02:22 pm

Found this in my owners manual (2001 U320) when I was looking through the appendix for something else. Relevant to the latter half of this thread.

Re: Shifting Techniques

Reply #15 – November 04, 2021, 02:15:27 pm

An ISM 11 at 65 mph in 6th gear is going to be just over 1400 rpm. Works pretty good for me. I don't need to burn more fuel nor do I want to go 70 mph. 57-58 mph in 5th gear increases the RPMs but seems to do bit better on MPG.

Every engine, every driver, every route is different. Drive a speed that feels safe and comfortable to you. A high stress day of driving is not much fun. A 350 mile day going 70 mph will get you there about 20 minutes sooner than 65 mph, with more stress and less fuel.

Re: Shifting Techniques

Reply #16 – November 04, 2021, 02:30:30 pm

Exactly,, What Roger said.
Relax on your journey. Don't save it all for arrival. Isn't that what most travelers do, FLY down the road to thier destination and then throw out the lawn chairs to look relaxed.

Re: Shifting Techniques

Reply #17 – November 04, 2021, 02:50:14 pm

On our last trip, we took the "scenic route" from Cedar City, Utah, roughly toward home. It turned out to be a very winding and narrow road. Part of the way up, the FT felt so sluggish. I am pressing the accelerator, but nothing seems to happen. I am thinking but not yet saying "it is time to change the fuel filters... I hope I can find a place to pull off."

Then I see the diesel truck behind us come close. I hear the screaming engine over mine and see the huge plume of black exhaust smoke. "Oh, I guess we are climbing a lot." The curves and scenery distracted me from that fact.

I think we went from 5000-ish elevation to 10,000ish in 15 miles!

Anyway, I am learning to shift like the coolant temperature is 20-degrees higher than actual, and the transmission 40-degrees higher than actual. I am learning that the retarder temp goes up quickly when worked, but drops quickly when given even a short break. Upshift, slow down, watch the gauges! We are told by SOMEONE that diesels have low-end torque, powerful at low RPMs. We somehow conclude that it is OK to drive long, (or steep) distances that way. There is a comfortable spot between babying the engine and flailing it.

Our previous RV, a Monaco had a definite speed "groove." At 62 MPH, things calmed down, the engine got quieter, the ride was smoother. I could feel 2 MPH above or below. Our FT - It calms around 64 MPH, but the "busy" feel does not come back at nearby speeds. I have accidentally been up to near 80MPH. Definitely not my style. Sixty-four is my groove.

I still long for an aviation-quality altimeter.

Re: Shifting Techniques

Reply #18 – November 04, 2021, 02:55:39 pm

My trans is programmed to start up in performance mode. I don't change that. Around town (from the house to the highway), I manually shift via the pad. I select 3rd on the pad and let it shift. About 45mph I let it go to 4th. In auto, it will be in 4th, lugging at 35mph. I'll generally set it to 5th until I hit my desired highway speed, then up to 6th. All acceleration happens in 5th or below. 6th is just to maintain speed. Start up a grade, shift back to 5th.

ISM450/MH4000R

YMMV

Re: Shifting Techniques

Reply #19 – November 04, 2021, 02:59:12 pm

Quote from: oldmattb – November 04, 2021, 02:50:14 pm

I still long for an aviation-quality altimeter.

Chief Aircraft Inc. - Aircraft Parts, Avionics, Instruments, Pilot Supplies,...

Re: Shifting Techniques

Reply #20 – November 04, 2021, 05:43:15 pm

Chief is great but don't spend the bucks on a new one. Search Trade a Plane at Search For Aircraft & Aircraft Parts - Airplane Sale, Jets, Helicopters,... or Barnstormers at BARNSTORMERS.COM Find Aircraft & Aircraft Parts - Airplane Sale, Jets,... Nothing like the old altimeters where you can set the pressure manually. Even predict the weather this way. I like knowing the pass elevation ahead of me and then watch the altimeter go up as I climb.

Pierce

Re: Shifting Techniques

Reply #21 – November 10, 2021, 10:28:00 pm

Having read this post I decided I needed to watch rpm verses speed, do over the last few days we have gone from the hill country west of Austin over to Nacogdoches then on to Hot Springs AK. Without using the interstate
No real mountains but plenty of steeper grades.
U270 350hp Cummins, 6 speed trans in economy mode, towing a Jeep Grand Cherokee.
Set cruise at 65 mph and rpm held at approx 2100 on the flat, then the hills came and the transmission was faster than I could be at dropping a gear keeping the RPM above 1750 with very little drop in speed which I believe keeps us in the best torque area.
Shifting for going up hills the coach was better than I could be!!
Shifting down for descending hills I of course had the upper hand, retarder gets hot fairly quickly rendering it somewhat useless (wish I had a jake brake as well)
Determined that unless we are going up very steep hill I don't need to get involved with manually shifting.
David

Re: Shifting Techniques

Reply #22 – November 11, 2021, 08:21:17 am

Three points:

You can be PROACTIVE-- seeing what is coming up in front of you. Whether much steeper grade or you are almost ready to top the grade, only you can see that. The transmission is REACTIVE-- seeing what went on well behind you (coach momentum slows "reaction time".

There will be conditions where your transmission will HUNT-- shifting up/down/up/down because the grade is just a little too steep for the higher gear. Use the down arrow to lock the transmission in the lower gear until grade changes and the transmission will choose A gear.

Also, if coolant temperatures start rising, best to choose a lower gear where engine RPM is toward the top of its RPM range AND at less than full throttle. Unless you down arrow to that gear, the Allison will upshift.

Re: Shifting Techniques

Reply #23 – November 11, 2021, 10:18:08 am

I shift mine manually on hills to keep things turning 17-2000 RPM. The same goes for speeds zones 55 5th, 45 4TH, and so on, keep the rpm's up and keeps the trans from continuing to try to hunt (up and down shifting)

Re: Shifting Techniques

Reply #24 – November 11, 2021, 10:38:38 am

Ours shifts OK on the hills but with the 4 speed, it would hunt between 3rd and 4th on many grades if I let it. That is annoying and not good for the drive train either. In summer when the temps are high, I downshift and back off the throttle as necessary to keep the gauge under 200.

Where was the Roadranger option back in '93?

Pierce

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