Manual Shifting

[akadeadeye]

I have yet to use manual shifting on our Allison 3000 and ascending and descending mountains has worked out OK just letting the tranny do its job and assisting on the descent with the engine brake. But I feel like I should know how and when to downshift to enable more RPMs on the ascent (to keep heating to a minimum) and to assist the descent in addition or instead of the engine brake.

We are headed to the Rocky's this week. What do you do?

Don

[wolfe10]

Don,

Let's start with the good news-- the Allison ECM is idiot-proof. No matter what you do, you can not mess it up. Down arrow 6 times at 60 mph and nothing bad will happen. The Allison KNOWS that you mean when it is safe to downshift a gear at a time, do so. It will not overspeed the engine.

You are (or with a little practice WILL BE) smarter than the Allison ECM. Why-- because, it is REactive-- seeing what happened behind you (and with a heavy coach, momentum dictates a good ways behind you).

You can be PROactive-- seeing what is happening in front of you. You can see that you are about to top a grade, the grade is about to get steeper, etc.

The up and down arrows are your friend. The most "manual" way to drive the Allison is to leave it in Economy mode all the time and use the down and up arrows to select the proper gear for the conditions you are in and the conditions you see just in front (not behind) you.

Remember back to driving a manual transmission car-- whether a VW bug or all out sports car, you can decide to optimize the way your engine/transmission act.

You can fine tune it, or you can let it do its own thing-- your choice.

[akadeadeye]

Brett, Thank you for your response. This is the best explanation I have read yet from anyone. If I decide to downshift near the crest of the climb am I still OK using the engine brake on the descent?

So, I should choose Economy Mode for all driving conditions?

Don

[wolfe10]

Don,

You can change gears using the up/down arrows anytime you want, and as often as you want.

As far as using the engine brake (don't know whether you have an engine compression brake or exhaust brake-- the ISL could be ordered either way) along with activating the engine brake, the Allison starts downshifting toward the "pre-select" gear. That is the gear that has been programmed into the Allison. It can be any gear, but 2nd and 4th are common choices. So the transmission may already be programmed to downshift further than your selection for climbing.

Yes, you can drive in economy mode anytime you wish. I use it 99% of the time. The only time I don't is if am willing to say "I will pay a lot of fuel for a little more performance". Example, passing on a two lane road. But economy mode also makes driving less "automatic", as engine temperature rises with full throttle, low RPM use. So, if a long grade causes engine temperature to rise, in economy mode, you may need to manually down arrow to a lower gear. This is what I do, and have for over 200,000 DP miles. Economy mode also follows your engine manufacturer's advice for "most economic way to climb a grade" which is just above peak torque RPM.

[akadeadeye]

Great information Brett. Thank you.

Don

[tbutler]

I'm trying to recall the last time I used the manual downshift. I'm sure that I have but it is a really rare occasion for me. I drive in economy mode almost all the time, the exception is when I forget to hit the mode button when I start driving after an engine shut down.

I drive almost all the time with cruise control. On flat country that is a no brainer, set it and forget it. In hill country when I top a hill I'll hit the set button on the smart wheel which notches the cruise setting down 1 MPH each time I hit the button. After hitting the button three to five times the turbo drops to zero and I'm coasting over the hilltop. Yes, I'll slow down a little and this frequently allows me to descend the hill, accelerating while coasting, without using the engine brake to keep my speed under the 65 MPH speed limit on my toad. If the speed approaches 64 MPH I'll engage the first stage of the engine brake and if it goes on to 65 and increasing I'll engage the second stage of the engine brake and use additional braking as needed. The engine brake does the downshifting for me. Near the bottom of the hill, I'll disengage the engine brake and notch the cruise control up by hitting the resume button on the smart wheel as needed to notch the speed up 1 MPH per hit until the setting matches our speed. This all works well because I have the Aladdin System display on the dash which displays the speed, cruise control setting and the turbo boost level. It also displays engine and transmission temperature and the instantaneous MPG.

If the hills are really big I'll have to drop the cruise setting incrementally to keep the turbo from going to 100% which will trigger a downshift on the uphill as the speed decreases. When speed drops below 57 the transmission downshifts into 5th gear automatically and the turbo boost drops. Once again I'll drop the cruise speed as needed to keep the turbo just below 100% until the speed is below the limit for 5th gear and the transmission automatically downshifts into 4th gear. This works for mountain slopes as well, as the speed drops to the minimum for any gear the transmission will automatically downshift, RPM goes up and turbo boost drops. At the top of the hill I'll cancel the cruise control and coast over the top of the hill purposely allowing the speed to drop. Going over the top of the hill I assess the descent and then engage the engine brake as needed. If it's a long or steep hill I'll engage the engine brake right away if not, I'll coast downhill until near the speed limit for the toad. I've never had a problem with engine or transmission temperature using this method.

All that said, on two lane roads with traffic behind me, I don't use this method as the fluctuations in speed would irritate following drivers. I'll try to maintain speed as much as possible on hills which means more manual throttle on the way up the hill and more engine brake on the downhill which is more wasted energy and more fuel usage. On multi-lane highways if traffic is really heavy (I-35 between San Antonio and Dallas) I'll also abandon this method to help with traffic flow.

Keeping up with the changing road conditions and making adjustments requires a certain amount of concentration which also keeps me alert and helps me avoid white line fever. I believe that it also is more energy efficient and helps to boost my fuel mileage.

[wolfe10]

Tom,

I totally agree that there is no single "best" way to drive. Without the on-steering wheel control, your method would not work for our coach, as hand would be off the wheel too much of the time.

[tbutler]

Yes, being able to keep both hands on the wheel and manipulate the cruise control makes it workable. The information that the Aladdin System provides allows me to refine the decisions that I make. Without either of these assets, it would be very difficult.

[bizsmith@yahoo.com]

I usually only use manual shifting when I am in an area with slight grades. There is a certain grade where the transmission tends to shift up and down more than I like and I will usually shift down to 5th. I know it does not hurt the transmission but my personal preference is to use 5th because the automatic shifting tends to bug me.

[wolfe10]

Yes, one of the times that it is very helpful to the drivetrain is when the transmission is "hunting". That is your speed/grade are a little too much in the higher gear, so the transmission is up/down/up/down shifting.

You will do your drivetrain a lot of good by using the down arrow to lock the transmission in the lower gear.

BTW, this applies to all vehicles, not just DP's.

[akadeadeye]

Brett, How do you benefit from using the Economy Mode?

Don

[wolfe10]

Don,

From an article I wrote for the FMCA Magazine:

ALLISON TRANSMISSION MODE BUTTON

BY BRETT WOLFE, F252125

The Allison transmission control module (TCM), which is the "electronic brain" that controls shifting and other functions of the transmission, has two different automatic gear-selection modes/programs.

In Economy Mode, the transmission will not downshift even at wide-open throttle until the engine pulls down to peak torque rpm in some applications and 200 rpm lower than Performance Mode in others. In Performance Mode, the transmission will downshift much earlier to maintain higher engine rpm.

Only at higher throttle positions is there any difference, so on flat ground you will not notice any variation between the two modes, except when accelerating from a stop if you are at or close to wide-open throttle.

However, mode selection can make a big difference when traveling over rolling hills. If you drive in such areas while in Performance Mode (particularly with the cruise control on), it is common for the transmission to shift down to fifth gear on the uphill and back to sixth gear on the downhill, repeating this process hundreds of times. In Economy Mode, the transmission will stay in sixth gear unless the hill is so steep or so long that the engine cannot pull it without dropping below peak torque rpm. According to engine manufacturers, the most economical way to climb a hill with a modern turbocharged diesel engine is in a higher gear (lower engine rpm), provided the engine doesn’t overheat.

If, while driving in Economy Mode, you know you will need a lower gear because of the steepness of the grade and/or the engine temperature is rising higher than the thermostatically controlled temperature, use the down arrow to drop a gear (this is what I do) or switch out of Economy Mode. Be sure to switch back into Economy Mode when past the steep section or you will be stopping at a service station for fuel sooner than you expected.

While you are driving in hilly terrain, if your engine begins to overheat, the engine’s horsepower-to-weight ratio is low, or it irritates you to lose a few mph in the name of saving fuel, by all means drive in Performance Mode.

It confuses me to hear people advocate driving in Economy Mode only on flat ground, as there is not 1 percent difference in shift rpm between Performance and Economy modes on flat ground, except when accelerating from a stop if you use wide-open throttle.

Every time you start the motorhome, the transmission is in Performance Mode. This is the default setting. If you push the mode button, it goes to Economy Mode and the light illuminates.

There is no absolute number that can be given to illustrate the difference in fuel economy that will result when driving in Economy Mode. On flat ground where you will be in sixth gear no matter what mode you are in, there will be zero difference. The most significant difference in mileage will occur in rolling hills, where in Performance Mode, particularly if on cruise control, you will start up a hill in sixth gear, go to wide-open throttle in that gear, and downshift to fifth gear still at wide-open throttle, where it is using a lot more fuel. After the hill is crested, the transmission will upshift to sixth, then likely coast a little in that gear unless you are driving with the exhaust brake on. If you are, the exhaust brake will be applied and the transmission will downshift toward the preselected gear, which is generally either second gear or fourth gear. And so the process will continue, with the transmission shifting up to sixth gear on the downhill, back down to fifth gear on the uphill, etc. The problem with this is that a modern turbocharged diesel engine is much more efficient at low rpm with high throttle settings.

Note: In either mode, you are free to use the up and down arrows to proactively choose the correct gear. You cannot screw anything up, even if you downshift to first gear at 70 mph. The transmission circuitry understands that you want to downshift to the next lower gear as soon as the engine rpm will not exceed the preset amount. Then it will downshift again when safe.

By the same token, you can shift between Performance and Economy modes as often as you want with the transmission in any gear when you make the change.

I drive in Economy Mode 99 percent of the time, including in the mountains. I use the up and down shifting arrows to choose the proper gear. I use Performance Mode only to pass another vehicle on a two-lane road, when I am willing to sacrifice a little fuel economy to gain a short-term burst of speed.

[akadeadeye]

Thank you for your knowledge and your time, Brett.

Utah here we come.

Don

[wildebill308]

Don, go have fun. Utah is the only western state I didn't hit this summer. You didn't say if you have the engine brake or the transmission retarder. I have the transmission retarder and when that is turned on and lift on the throttle it will try to down shift to second gear. This is helpful when going down hills or coming up to a stop sign. You don't need to manually downshift going down hill just let the engine slow you down. If it isn't holding enough use your brakes to slow down enough to get into a lower gear. I only had to get down to third a couple of times where it was a very steep grade. You don't have to worry if it starts to go to fast in the lower gear it will up shift to prevent over reving the engine. Then you can apply your brakes to slow it back down. Just do not ride your brakes as they will heat up and you could end up with no brakes. The only negative I have heard about locking it in a lower gear is if it won't hold the speed in that gear and accelerates to where the engine rpm is too high and you can damage the engine.

Lots of good advice on climbing. I watch my EGT gauge and if it starts to get to high I will manually downshift or if the water temp starts to go up. lots of people talk about climbing steep hills and having high temps but I found the case where it was a gradual grade and the transmission on cruise could stay in 6th but the boost was running 35psi ( flat land it is 12-15psi) and the water temp and EGT was getting to high. I had to slow and drop to 4th for a while till things cooled off then I was able to pull 5th.

You will find what works for you.

Bill

[wolfe10]

Bill,

Just a clarification-- with the Cummins B and Allison 3000 in your chassis, you very likely have an exhaust brake of some brand. Later model B engines used VGT turbos and did not have an external exhaust brake.

The only coaches with retarders (built into the Allison) are some OTR buses and Foretravels.

The names/brands of the exhaust brakes makes it difficult to understand, as some are called/labeled retarders.

Look at the downstream side of our turbo in the exhaust system and verify what you have. I say this because some, like PacBrake require lubrication.

[akadeadeye]

I do not have a transmission retarder. I do have a switch that is labeled "engine brake". And, I use it quite often on steep grades where I want to maintain a certain speed.

Don

[wildebill308]

Yes the wording is different between the owners manual and the transmission manual. The owners manual calls it a compression brake and the switch is labeled "engine brake" while the transmission manual calls it a retarder.

I have looked at the exhaust closely when I installed the new muffler there is nothing after the turbo. When I was doing my fluid change I asked and the Allison shop said I had the retarder. I sometimes think I could get better mileage with it turned off as if you lift a little to much it kicks in and starts to slow you. I have gotten use to it and seldom turn it off. I guess I like that extra braking more than the potential mileage.

Bill

[wildebill308]

Don, mine is labeled "engine brake" to.

Bill

[tbutler]

I have looked at the exhaust closely when I installed the new muffler there is nothing after the turbo. When I was doing my fluid change I asked and the Allison shop said I had the retarder. I sometimes think I could get better mileage with it turned off as if you lift a little to much it kicks in and starts to slow you. I have gotten use to it and seldom turn it off. I guess I like that extra braking more than the potential mileage.

Bill

I have heard of others who drive with the engine brake/exhaust brake/retarder on all the time. It is cutting your fuel mileage. If the only states for your vehicle are power and brake you are missing out entirely on coasting. Coasting is when no power is applied but you are using the momentum of your vehicle to propel you forward, sometimes for very significant distances. I'm not talking about coasting with the transmission in neutral, I'm talking about coasting, simply not applying power, foot off the accelerator. Think about it, I'll bet you don't take your foot off your car accelerator and immediately start pressing the brake pedal. Only in an emergency situation would you drive like that.

When you are applying power, you are adding energy to the vehicle. If you apply power until you have to brake you are powering the vehicle much longer than necessary, wasting fuel. Taking your foot off the accelerator and having the automatic braking come on immediately turns that power into waste. If you drive in a manner to apply just the power necessary to get you to the next stop sign or signal and then coast to the stop sign you will be taking full advantage of the power you have already applied. When I approach a town I begin coasting to slow from my cruise speed to their speed limit. Easiest when you know the territory and the speed limits but can be done anywhere. I look for water towers or grain elevators as an indicator of a town. My GPS has shaded areas for towns and these show up two miles ahead when in cruise speed so that helps me know when a town is coming up and I'll start slowing down. Sometimes towns or states post reduced speed ahead signs which are helpful for avoiding sudden or hard braking.

I'm not suggesting that you coast all the way to a stop at the stop sign. No one is that precise in their judgement of the momentum in the vehicle. I am suggesting that you attempt to do that with the hope that only minor braking will be necessary to bring you to a full stop. This has an added advantage with stop lights. If you slow down well in advance of a red light you increase the chance that you will arrive at the light after traffic has started to move. If you can avoid a full stop you avoid the lower, less efficient gears and significantly increase your fuel mileage. Watch carefully and you will see most truck drivers doing this. Roaring up to a stop sign and coming to a screeching stop is something that you hardly ever see from truck drivers.

In short any time you apply the brakes, you waste energy and energy is fuel. The harder or longer you have to apply the brakes the more energy you are wasting.

So how do you use the engine brake/exhaust brake/retarder? Mine is always off. I use it when necessary for additional braking. I use it on downhill slopes to avoid overspeeding. See my post above for techniques to avoid or minimize braking on downhill slopes. I use it when approaching a stop sign or signal if necessary but to be used minimally or completely avoided if possible. I use it in emergency stop situations. I watch traffic very carefully and at any sign of congestion or emergency condition I will immediately place my hand on the engine brake switches (I have a 2 stage engine brake) at the same time I remove my foot from the accelerator and place it over the brake pedal.

I'm retired, driving a large thirsty vehicle, not a race car driver.

[wildebill308]

I have heard of others who drive with the engine brake/exhaust brake/retarder on all the time. It is cutting your fuel mileage. If the only states for your vehicle are power and brake you are missing out entirely on coasting. Coasting is when no power is applied but you are using the momentum of your vehicle to propel you forward, sometimes for very significant distances. I'm not talking about coasting with the transmission in neutral, I'm talking about coasting, simply not applying power, foot off the accelerator. Think about it, I'll bet you don't take your foot off your car accelerator and immediately start pressing the brake pedal. Only in an emergency situation would you drive like that.

When you are applying power, you are adding energy to the vehicle. If you apply power until you have to brake you are powering the vehicle much longer than necessary, wasting fuel. Taking your foot off the accelerator and having the automatic braking come on immediately turns that power into waste. If you drive in a manner to apply just the power necessary to get you to the next stop sign or signal and then coast to the stop sign you will be taking full advantage of the power you have already applied. When I approach a town I begin coasting to slow from my cruise speed to their speed limit. Easiest when you know the territory and the speed limits but can be done anywhere. I look for water towers or grain elevators as an indicator of a town. My GPS has shaded areas for towns and these show up two miles ahead when in cruise speed so that helps me know when a town is coming up and I'll start slowing down. Sometimes towns or states post reduced speed ahead signs which are helpful for avoiding sudden or hard braking.

I'm not suggesting that you coast all the way to a stop at the stop sign. No one is that precise in their judgement of the momentum in the vehicle. I am suggesting that you attempt to do that with the hope that only minor braking will be necessary to bring you to a full stop. This has an added advantage with stop lights. If you slow down well in advance of a red light you increase the chance that you will arrive at the light after traffic has started to move. If you can avoid a full stop you avoid the lower, less efficient gears and significantly increase your fuel mileage. Watch carefully and you will see most truck drivers doing this. Roaring up to a stop sign and coming to a screeching stop is something that you hardly ever see from truck drivers.

In short any time you apply the brakes, you waste energy and energy is fuel. The harder or longer you have to apply the brakes the more energy you are wasting.

So how do you use the engine brake/exhaust brake/retarder? Mine is always off. I use it when necessary for additional braking. I use it on downhill slopes to avoid overspeeding. See my post above for techniques to avoid or minimize braking on downhill slopes. I use it when approaching a stop sign or signal if necessary but to be used minimally or completely avoided if possible. I use it in emergency stop situations. I watch traffic very carefully and at any sign of congestion or emergency condition I will immediately place my hand on the engine brake switches (I have a 2 stage engine brake) at the same time I remove my foot from the accelerator and place it over the brake pedal.

I'm retired, driving a large thirsty vehicle, not a race car driver.

You are right but I will continue to drive with it on. I can with careful use of the accelerator pedal coast as mentioned. You cannot turn on the switch fast enough in an emergency situation. I also use the cruise control about 90% of the time.

Bill

[JSPERRELLA]

Mine does not come on until I hit the brake or press cancel on our cruise control. Check if your programming can be changed.

[wayne77590]

We have been on the road since June 13th - this year. Across FL panhandle, up the East Coast to NE. Across to Niagara, then across lower Canada to MI. Up to St Ignace around the top and down the western side of Lake Michigan. Stopped in Apple Valley, MN and a few more stops and presently in Kansas City, MO. I use cruise control extensively, like it is on all the time except in those situations whare I have to slow down, or through a town/city. My exhaust brake is always on. About the only time I'll turn it off is when I first start out and want to dry the brakes out after a rain.

When I hit my brakes I want the exhaust brake to help slow me down, and it does a fine job. I cruise at about 62-63 mph. going down some of the longer hills I'll creep up to 65 and the cruise control seems to hold me there. On occasion a steep hill will creep me up past 6mph over my set speed. At that time my exhause brake kicks in and assists in maintaining a comfortable speed. All other times I slow down I do not want to coast, I want to slow and most likely quickly.

I use economy mode exclusively and only down shift to 5th when it starts going up and down. On the hills here in Missouri I cruised at 62 and many of the longer grades it never shifted out of 6th hear. On other hills it shifted to 5th and occasionally to 4th. I was very happy with the performance in economy mode.

I have an ISB 340 with an Allison 2500 transmission, pulling a 2013 Lincoln MKX.

I'm sitting at 9.2 mpg at this stop and that is the average for this entire trip.

What am I doing wrong.

[bizsmith@yahoo.com]

My engine brake can be applied with a foot pedal and I use it a lot. The air brakes are only used for the final stop.

[wolfe10]

Yes, there are a number of ways that the engine brake (exhaust, compression or VGT) can be set up from the factory and then used by the driver.

I do know that Caterpillar offers what I feel is the "ideal" factory set up. It is called Latch Mode. When the Caterpillar ECM is programmed for Latch Mode (by any Caterpillar dealer) and assuming the chassis maker has wired the ECM with brake switch input, here is how it works. Leaving switch ON all the time:

Take your foot off the throttle-- you coast (like Tom, this is my favorite "gear").

Touch the brake pedal-- the engine brake comes on and stays on whether you stay on the brake pedal or not. Engine brake turns off when the throttle is touched.

This allows the engine brake to be left on all the time for emergency stops, yet allows you to coast.

If someone knows if Cummins offers the same, would be interested to know.

[wayne77590]

Breit, that seems like a very nice feature, and logical. Probably why it's not on more systems.