A Couple of Tranny Questions

[Dick Simonis]

First, does anyone use the "economy" mode on the tranny selector??  If so, under what conditions and is the affect noticable?  The folks at Beaver Coach were less than enthusastic about it.

2nd, how should I properly use the engine brake.  On my trip from Bend to Lebanon, I just left it on 3 cylinder all the time and popped it over to 6 cylinders if I needed more braking.  I neved did manually shift the tranny to lower gears which seems in retrospect like an error in judgement as it did a lot of shifting when I applied some accelerator.  Also  the tranny never shifted to 6th even on flat land which I suspect was the engine brake locking out 6th gear.

Thanks for any input.

[Gerald Farris]

Dick,
I always drive with the transmission in economy mode. You will not notice any major changes in the way that the coach performs, however the economy mode will lower the shift points slightly and it will also reduce the amount of downshifting that the transmission does under normal driving.

Second the engine brake usage is determined by your personal driving taste and the terrain that you are driving in. Interstate 70 across Kansas does not require it at all. However the same Interstate across western Colorado will require it a large portion of the time. So some drivers leave the engine brake on all of the time and some drivers like me only turn it on when needed. Although on your coach the cruise control will not operate with the engine brake turned on, so you have to decide which one you want to use.

On the coach not shifting into 6th gear, the engine brake only effects the transmission shifting when you are not apply throttle. If you are accelerating the coach will shift normally until you release the throttle, then it will downshift to 4th and begin to brake the coach. You did not say what speed you were driving when the coach was expected to shift into 6th a and did not. On your coach the transmission will not shift into 6th until about 60 MPH on level ground. Economy mode will lower that shift point about 2 MPH.

Gerald  

[Dick Simonis]

OK that makes sense.  I never got above 55 on the trip so it makes sense that it didn't shift to 6th.  And yes, I found out the hard way that the engine brake disables cruise control....I thought it was inoperative until I thought about it a bit and turned the brake off.  There are so many interlocks I just figured that maybe 6th was disabled also.

[Gerald Farris]

Dick,
One thing that you may want to consider doing if you use the engine brake a lot is to have the transmission reprogrammed to either not downshift or only downshift to 5th instead of 4th. The reprogramming issue was discussed on several threads on this forum. One that specifically addressed this issue is:  http://forum.bacrallies.com/m-1308661187/

Gerald  

[Bill Sprague]

Dick,

I think you are asking how others do it, so I will offer my version.

As Gerald said, habits vary.  After 90,000 miles my habit is to leave the exhaust brake off, leave the shift pad alone and set the cruise control to 60.  At 60, my rig will get to 6th gear and stay there, except for hills.  Leaving the shift pad alone with cruise on means the engine, transmission and cruise control computers will do the mechanical work while I do the "defensive driving".  I like to keep my eyes on the traffic, rather than the tach.  

When I remember, I do select the Economy mode, but I can't prove it saves any money.  I think that if this transmission were in an application where most of the driving was in town with lots of shifting, it would make a difference.  In a motorhome where we are mostly on the highway at cruise speeds the transmission is pretty much "stuck" in the same gear until we climb a hill.  

Regarding exhaust brake use, my habit is to leave it completely off most of the time because I use the cruise control.  Going down hills is a different story!  My goal is to use the exhaust brake in a way where I don't use the service (or foot) brake at all.  On long hills I like to reserve the foot brake for emergency stops. I don't want them hot from use. So, at the top of a typical 6% freeway grade I turn on the exhaust brake which releases the cruise.  On mine, the Allison is programmed to try to reach 2nd.  Of course, it won't but it will downshift to something that will slow it some.  At the crest of the steep part I want to be at about 47 mph where my Allison will shift to a gear (3rd or 4th?) that puts the engine at about 2500 rpm.  The braking effect is very good and I can go down a long hill without using the service brakes except for minor short taps if the RPM climbs.  On my coach, with a Cummins, the Allison does not up shift until it goes over 2700 rpm.    

I've never wanted to cruise below 60 mph.  I thought it was important to cruise at a speed that would get the Allison to 6th gear.  On my last trip, I tried 55 and never got to 6th gear.  The purpose was to see what differences were in fuel mileage.  Using the Aladdin as a reference, I got over 9 mpg.  The Aladdin says my lifetime average is 8.0.  At $4 per gallon, the difference may be enough for me to never see 6th gear again!

[Glenn Perkins]

Hi Bill,

In my experience, use of the Economy mode causes the transmission to shift less (lowers the shift point so that you have less shifting down on level going) and I use it while using cruise control on the open road.

And I use the Jake only when I want to slow down or maintain speed on a long downhill or need to make a quick stop for traffic.

Hope that helps.
Glenn

[Joel Ashley]

I have to agree with Bill, and have come to drive in much the same way that he describes.  On our last trip from Portland to Twin Falls, I stayed as close to 55 mph as posted speeds would allow (faster on Idaho's I-84), which meant 5th gear, used Economy Mode and cruise control, and turned on the Exhaust Brake going down hills, the same way Bill does.  As I recall from an Allison seminar in Harrisburg in 2007, the shift to 6th won't occur until nearly 60 mph, as Gerald mentioned.  At the time, Allison was considering lowering that shift point with a software change because of owner pressure, but their tests indicated they already had the most efficient configuration.  I don't think they ever changed it;  I believe individual owners could have it changed if they really insisted.  My take was that Allison probably knew best.

I had calculated needing to fill my tank in Baker City, but at that point I had far more fuel than expected and so stayed on the road. I couldn't believe we had so much fuel left by the time we got to Twin that night.  After topping off before the next leg of the trip, I calculated we'd gotten nearly 10 mpg;  this on a CAT C9 with only about 9000 miles on it at the time, and not "broken in".  If we hadn't been forced to higher posted speeds in the Idaho section, we might have done even better.  

I can only believe that the combination of cruise control nearly all the way (except the steepest hills), Economy Mode, good weather, and conservative speed led to such good numbers.  The cruise control was probably the biggest factor because it is far more steady on the throttle than the human foot, which tends to microburst the throttle imperceptably.

Adapt Bill's methodology and you should do just fine, Dick.  The only issue I've discovered is the touchiness of the exhaust brake going down hills;  sometimes if I slow too much and try to compensate with the throttle a bit, the coach lurches on and off annoyingly.  You have to learn to control that with a light touch, but it's tricky.

-Joel

[Bill Sprague]

In my experience, use of the Economy mode causes the transmission to shift less (lowers the shift point so that you have less shifting down on level going) and I use it while using cruise control on the open road....

Glenn,

Mine does not shift very often whether the Economy mode is on or off.

Bill

[Bill Sprague]

......I can only believe that the combination of cruise control nearly all the way (except the steepest hills), Economy Mode, good weather, and conservative speed led to such good numbers.  The cruise control was probably the biggest factor because it is far more steady on the throttle than the human foot, which tends to microburst the throttle imperceptably.....

And don't forget wind.  Headwinds are bad, tailwinds are good!  And, wind has a bigger effect than the Economy button!

[Joel Ashley]

You are right indeed, Bill.  The only thing is that the general wind direction for a substantial portion of that trip was from the east, in my face.  The Columbia Gorge and points east summer and fall air flow is from the hot high desert to the cool Willamette Valley.  Perhaps I caught some westerlies out of the Blue Mtns. through the Boise stretch.

-Joel

[Keith Cooper]

I have a comment and a couple questions.
One thing I have noticed is that when the transmission is in the economy mode and the Jake brake is engaged the downshift is harsher and more apparent. I assume this is due to the wider range in the secondary shift schedule.
As to the Jake brake what is the general feeling: Should the ECM be set up for manual, coast or latch mode? There is a pretty good description of the three modes at (http://www.fabickcat.com/powersystems/docs/purepower/engines/Cat_Compression_Brake.pdf ) personally I am leaning toward changing to coast mode.
As far as cruise control is concerned there are two modes hard cruise and soft cruise. Which mode is optimal for economy? Soft cruise allows the coach to coast a few MPH above where the cruise is set and also allows speed to drop a few MPH below cruise speed before downshifting, when climbing.  

[Dick Simonis]

That's an intersting article by Cat but I notice it's for the C11, C13, and C14 engines.  My C12 is not included.  I have three positions:  Off, 3 cyl., and 6 cyl.  When I let up on the go pedal, it just brakes with whichever was selected.  As far as I can tell my cruise control is merely on or off.  If there is a hard or soft I have no idea how to access them.

[Keith Cooper]

Dick,
I have been following your post probably should have started a seprate thread to address the questions, sorry.  
One of the parameters in the ECM allows control of the Jake brake to be managed thru the brake pedel when the cruise switch is on. My understanding the the Jake Brake operates thru the switch on the panel when the cruise control switch is tured off.
A second ECM parameter allows the cruise control function to be changed to soft which should reduce upshift and downshift frequncy when the cruise control is active.
The next time i take the coach into a Cat dealer for any service i plan to request a printout of the ECM parameters and have the appropriate changes made at that point.

[Gerald Farris]

Keith,
My 2000 Marquis is wired to prevent the cruise control from operating when the Jake is turned on, and I think that your coach is wired the same. I was told that it is a very easy wiring change to get the cruise to work with the Jake turned on and the Jake then will come on only after the brakes are applied to disengage the cruise control, but I have never looked into it since I was not interested in the change.

Gerald

[Keith Cooper]

Gerald,
thank you for the information. I will defer the ECM changes to the Jake brake, for now