Shifting your Allison Transmission.

[slemnah]

My CAT C13 pulls the grapevine at around 1540rpm with the cruise set to 62 at the bottom of the hill. Temp remains constant and I let the ECM and TCM decide what gear I need to be in and what rpm it likes the best. I just sit back and enjoy the ride! My coach weighs 42k lbs and I usually tow a 23 ft trailer with my vehicle in it.
Steve
05 Panther

[Coma]

This can be made simpler by reviewing a few definitions.

Torque is force about a point. There is a more complex definition to cover all angles but this works here.

Force over distance is Work. Moving your wheel in a circle takes Work.

Work done over a period of Time take Power. Horse Power. Any measure that has a time rate of change requires Power. Like revolutions per Minute. Like miles per Hour. Going up a hill faster means higher miles per Hour.

As a aside, Cummins has several engines that produce power in the 300-370 HP range, the ISB, ISC and the ISL. Be sure for clarity to mention which model engine.

[mel s]

Originally Posted by WillandJane

.....while I have some clue, I am wanting to get a better grasp on manually shifting my Allison transmission to of course strive for maximum efficiency. Most go with the put your foot on the gas and let Allison do the work but those that don't, as your climbing the hill....what are you looking or listening for to shift from say 6.5 using the down arrow to go to 6.4, 6.3 and so on or is it more radical and the shift being from 6.5 to 6.0 and 5.5 and so on.
WDK

WDK
I have always let the transmission do the work
However the information in this pdf may be helpful: http://www.rvtechstop.com/resources/...s/allsonok.pdf
Mel
'96 Safari

[Dr4Film]

Originally Posted by CountryFit

so many people are running at 2000+ rpm on uphills... well, i am not sure, i could be wrong, to be honest, i have never run at that rpm. my engine max torque is at 1400-1600 rpm. to get the best economy, on uphills i normally low the gear to maintain at 1600-1800 rpm. anyone else does this?

Originally Posted by Coma

Cummins has several engines that produce power in the 300-370 HP range, the ISB, ISC and the ISL. Be sure for clarity to mention which model engine.

This discussion comes from owners that may have many different engines, Cummins, CAT & Detroit Diesel which are rated at many different horsepower's.

What coach brand, length, weight, etc. is totally irrelevant. It's how YOUR power plant that is in YOUR coach and how it performs while climbing a grade in conjunction with the size of your Allison Transmission that is the most important information to you.

Each one can be completely different than the next.

My coach has a Cummins ISC-350. When climbing grades I need to be around 2000 rpm's for best performance when climbing grades.

An ISB, ISL, ISM, ISX, CAT engines & DD-50 or 60 will most likely perform completely different than mine.

Bottom-line, Dutch Star Don had stated it BEST in a previous post, "So......the moral of the story......every coach is different and you really need to experiment when climbing and descending grades. If you wait for the Allison to downshift on it's own (on 6% grade or better) you'll drop below maximum power before the Allison will shift and it will be too late."

Dr4Film ----- Richard

[WillandJane]

Originally Posted by mel s

WDK
I have always let the transmission do the work
However the information in this pdf may be helpful: http://www.rvtechstop.com/resources/...s/allsonok.pdf
Mel
'96 Safari

In saying that, would putting it in cruise control up most any hill, steel grades be ok at say 62mph or would cruise control at that speed try to push the transmission and engine well passed its limits?

WDK

[Rich-n-Linda]

I use the cruise control at 65 mph, AND shift down to 5th on the big hills. Gets the RPM up to 2,000 where the ISL develops its maximum HP.

Works just fine and nothing gets anywhere close to it "limits."

[WillandJane]

Originally Posted by Rich-n-Linda

I use the cruise control at 65 mph, AND shift down to 5th on the big hills. Gets the RPM up to 2,000 where the ISL develops its maximum HP.

Works just fine and nothing gets anywhere close to it "limits."

Do you downshift manually and put it back in cruise control or does the transmission do it as necessary while you are in cruise control?

WDK

[DD788Snipe]

Originally Posted by Rich-n-Linda

I use the cruise control at 65 mph, AND shift down to 5th on the big hills. Gets the RPM up to 2,000 where the ISL develops its maximum HP.

Works just fine and nothing gets anywhere close to it "limits."

Dittos here. I manually downshift to 5th on long grades of 6-7%

[WillandJane]

Originally Posted by DD788Snipe

Dittos here. I manually downshift to 5th on long grades of 6-7%

Please forgive me for being absolutely detailed here.....my rig is brand new and as I said I have only driven from Indiana to California, mostly flat all the way and what hills I did encounter I only mashed on the pedal and let the coach do its thing and it climbed ever hill in the 60 plus miles per hour range but back to your thought.....if I were in cruise control, are you saying that the transmission will not find 5th gear on its own if its climbing a long grade of 6-7 percent to maintain RPM and that you must think ahead of it and shift manually.

WDK

[Steve Ownby]

Originally Posted by WillandJane

Please forgive me for being absolutely detailed here.....my rig is brand new and as I said I have only driven from Indiana to California, mostly flat all the way and what hills I did encounter I only mashed on the pedal and let the coach do its thing and it climbed ever hill in the 60 plus miles per hour range but back to your thought.....if I were in cruise control, are you saying that the transmission will not find 5th gear on its own if its climbing a long grade of 6-7 percent to maintain RPM and that you must think ahead of it and shift manually.



WDK

The reason for manually downshifting when facing a long 6% plus up grade is that your transmission can't know what's ahead. It shifts based on inputs from various sensors. For this reason, the Allison will always wait too late to down shift for optimum climbing rpm.

Your Cummins ISB develops peak torque at 1800 rpm and is governed at 2600 rpm. I'm guessing that when you are cruising at partial throttle in top gear, your RPMs are between 1800-2000. I'm guessing also that your max hp of 360 occurs at just under the 2600 max RPMs. For best performance and max cooling, you should climb long grades of 6% or greater at over 2400 RPMs.

[Bigd9]

Originally Posted by WillandJane

Please forgive me for being absolutely detailed here.....my rig is brand new and as I said I have only driven from Indiana to California, mostly flat all the way and what hills I did encounter I only mashed on the pedal and let the coach do its thing and it climbed ever hill in the 60 plus miles per hour range but back to your thought.....if I were in cruise control, are you saying that the transmission will not find 5th gear on its own if its climbing a long grade of 6-7 percent to maintain RPM and that you must think ahead of it and shift manually.

WDK

In my opinion, you're very smart transmission computer will downshift to 5th, and 4th and even 3rd if need be right on cue as the inputs dictate. No input from the operator is needed.

[Piker]

To each his own...

If you find yourself bothered by losing speed on a grade... start pressing the go pedal down a little further.

If your speed does not increase (or if it decreases) as you continue pressing further and further on the pedal, the tranny should eventually downshift.

If you feel like you've lost too much momentum by the time the tranny downshifts, then you will probably prefer downshifting manually as opposed to letting the Allison figure it out. If you're satisfied with your speed when the tranny shifted, then let the Allison do it's thing.

Either way... you should be good to go.

I prefer to shift manually on grades so that I can hold the lower gear for as long as I like, because personally, I don't want the tranny "hunting" for the sweet spot and shifting up and down more than it has to. Being human, I can look down the road and kind of "see the future" if you will. Our human senses and intuition can tell us whether the road ahead will require a lower gear, while the Allison's sensory input is limited to "the moment..." and is unable to predict road conditions.

Just my $.02

-cheers

[Happycarz]

I'm with you, CountryFit.


2008 Monaco Camelot 40' PDQ

[johnhicks]

I too kinda know what gear we'll want to be in uphill or downhill; by the time Mr. Allison decides to shift it always seems to be a bit too late, even to the point of having to go down two gears on a climb. It's because I can predict and Mr. Allison can only react.