Exhaust brake Downshift

[Ken Sair]

I am having new Transynd/Filters maintenance done on Friday. In addition I am having the Calibration changed back to original (it will now get into 6th at 63 instead of 57).

My question is this. I am not particularly happy with my tranny always trying to get to second gear. Sometimes that is to slow. I am considering changing the default from 2nd to 4th gear. I can then downshift one more gear as necessary (3rd or 2nd). As it is now when the coach slows to much I simply switch off the EB.

What are others doing and why? Are you happy with what yours is programmed to do? Or am I just swapping one inconvenience for another (turning it off vs a manual downshift).

Thaks in advance for all your input.

Ken 2007 Beaver Contessa

[Mike Nunn]

Ken,  I too do not particularly like the dramatic down shift into second gear. I know that the book says it will not down shift too far until the speed is within a certain range but it sure does gear down quickly. It looks Like there should be someway of programming two shifts in depending on the speed.

I was just curious as to how many miles you have on the coach before you changed the trans fluid and filters and is the first time you have done this. Good luck finding a solution to the shifting, let us know if there is a better way. Thanks mike

[Ken Sair]

Mike, I still have the original Transyd in it. I took delivery january 2007. So, thats 5 years and 4 months. The coach has 70,000 miles (it will have 71,000 when I get to Allison on Friday).

I just had it tested by JG Lubricants and while most of the news was very good, the Transyn did contain some contaminants (dirt) and the recommendation was to change the fluid. I had hoped it would last longer but no such luck this time.

I am going to have them check for an obvious point where dirt may be getting in (breather etc). I think though its just 5 years old and time to change it.

I am leaning hard towards the 4th gear preset rather than 2nd. Its very little effort to hit the down arrow and apply the brakes to slow it down allowing for the downshift to third.

Ken 2007 Contessa

[Gerald Farris]

Ken,
My coach has an engine brake (Jake Brake) instead of an exhaust brake, however the shift patterns should be very similar. I had my transmission default gear changed to 5th gear. To me 5th or 6th is a better choice than 4th, because you can use the engine brake to control your speed on the long downhill grades that you find out west that you want to drive 60+ MPH on, however they are steep enough that some speed control is needed. In these cases 4th gear provides to much braking and to many RPMs, but 5th or 6th is just right.

Why are you changing the shift program so that 6th is not engaged until 63 instead of 57? I believe in getting into 6th as soon as possible, because as a general rule, less RPMs means less fuel burned.

Gerald  

[Gil_Johnson]

Ken,

I too was would have Allison change the exhaust brake setting to down shift one gear at a time rather than the factory 2 gears.  Allison says this is an easy program change.  I'm curious as to how you had your factory 6th gear shift point changed to a lower RPM.  I tried and Allison would not do so without Allison and CAT engineering approval.  Unless there were other changes, why go back to the 63mph 6th gear upshift point?

As for dirt in the fluid, well that's part of the fluid's job.  The real question is the reading above Allison's recommendation.  If you've ever stopped on a dusting road then you know how much dust the radiator fan circulates in the engine compartment.  If your coach has spent much time on those kinds of roads, then higher than expected dirt readings might be expected.

Gil

[Ken Sair]

Thanks Gerald, I will defer to your expertise. Not to many problems here in the east, no mountains. I like the idea of me choosing the right gear instead of some arbitrary choice. 5Th it is.

Now, getting into 6th gear. The original calibration was great, with the exception of it would not upshift until 63 mph. Not to bad except, when on one lane highways/backroads it was difficult to get into 6th (for those 55/60 speed limits). So I had the calibration changed, and now can get into 6th at 57 mph, excellent. Sadly, that caused another problem, 4th and 5th gear. 1st-2nd-3rd shift OK, but it shifts into 4th and then 5th way to soon, severely lugging the engine. So, whenever I accelerate from a dead stop, I start out in 3rd and then manually shift to 4th-5th-6th, a inconvenience sometimes. I don't mind to much, but the wife hates it. She just wants to hit 'D' and go.

It will shift perfectly from a dead stop if I go 'wide open throttle' which burns a lot more fuel. So, I am going back to the original programming. All it means is I now have to drive 63 mph instead of 62 when on CC. Not really a big deal. I sure wish Monaco had had done it differently but they did not. After 70,000m miles I know exactly at what MPH (18-28-39-51-60 these are the speeds at which I upshift manually) I would like the tranny to upshift but I cant program it myself. I went back and checked my mileage from when new and there has been lttle to no change in mileage from the original and the new cal. So, I'm opting to go back to original for convenience sakes.

Gil, I had to get permission for the calibration change. Allison did not care, neither did CAT but I had to get a 'permission' letter from Monaco before Allison would change it. I had thought all would be the same except it would upshift sooner, but that was not the case. Changing 6th, changed all the shift point and not in a good way.  So, its back to original.

Thanks to all for your comments.

Ken 2007 Contessa              

[Jeff Watt]

I haven't really noticed a big problem with downshifting into 4th, but then again I haven't encountered too many steep/long hills. Is this re-programing that most Allison dealers can perform?  I am asking as I am headed to the west coast, Yukon and Alaska and there are likely hills there that I haven't encountered.

The 2 stage engine brake seems to work well in the situations I have encountered to date.

As an aside. for a coach with 525 HP it isn't exactly a sports car off the line. Once rolling and in 2 or higher there seems to be good acceleration. I did have a series of a "drag races" this past February 8, with a coach that had 400HP plastered all over the back.  I certainly couldn't keep up with him off the line.  :-/ Once I got into 2nd or 3rd then no problem. No idea of the other coaches weight although it was near enough a 40footer and towing a car as well.

I guess I shouldn't complain, but I'd like to be able to hit it at some intersections and actually have it move off quickly.

Jeff

[Joel Weiss]

As an aside. for a coach with 525 HP it isn't exactly a sports car off the line. Once rolling and in 2 or higher there seems to be good acceleration. I did have a series of a "drag races" this past February   with a coach that had 400HP plastered all over the back - I certainly couldn't keep with him off the line.  :-/ Once I got into 2nd or 3rd then no problem. No idea of the other coaches weight although it was near enough a 40footer and towing a car as well.  

Jeff

Without turning this into one of those endless torque/horsepower discussions, bear in mind that your engine only develops its max rated horsepower at close to its redline.  The "off the line" performance is largely going to be governed by the low end torque and the gearing.  Your C13 has as much or more torque than most things out there unless they're running C15's or ISX's.  If you were using the ECON mode on your transmission during your drag races that would have resulted in faster upshifts and slower "0 to 60" times! LOL    So the performance difference you noticed was probably due to a lot more than just the 525 vs 400 comparison.  

What I have also noticed is that the coaches with "400 plastered all over the back" usually use smaller diesels like the ISC with ECM's set to produce 400HP at max rpm.  I would guess this to be because it is a lot cheaper to "chip" an ISC than it is to use an ISL or ISM in order to be able to advertise the HP (since the public has no understanding of torque).   To give the smaller engines the off-the-line performance desired I think the gear ratios are changed, just like would be done with a car, so that "speed in gear" is increased.  It will develop its rated HP in each gear at lower road speeds than we do which means it will be quick off the line but will be "running hard" at high speeds.  

It's like comparing a fine German automobile with a 4+ liter V-8 to a box on wheels running a turbo-4.  The German will cruise effortlessly at 60+ mph and still have plenty of oomph to get to 100 when passing on 2-lane roads.  You can tell what kinds of cars I used to drive and why I drive a 32,000 MH with 1500 ft-lbs and 425 HP!  LOL

[Gerald Farris]

Jeff,
There are two possible causes for your lack of acceleration from a stop. First is turbo lag, since your coach has two turbos that are in series, it will take a little longer to spool-up both turbos to reach the needed boost, but not to long. The other possibility is the fact that Monaco used an under sized air intake system on the 2005 C-13 coaches, and if that has not been corrected you could have too much intake restriction. I believe that this topic has been discussed on this forum before.

Gerald

[Mike Nunn]

Ken,  I do not think that in our coach down shifting from 6th to 5th would be enough braking to slow the coach all that much. While the shift from 6th to 2nd seems to me to be way too much too quick.  If I was going to change ours (which I do not have any plans on) I think that 3rd or 4th would be worth a try. I suppose just reaching over and pushing the button gives us other options.  I am not sure which coaches have the two stage, but that seems like a great solution.  Wish it was on our coach.

Mike

[Gerald Farris]

Mike,
The two stage engine brake is only on coaches equipped with a compression brake("Jake Brake"). Some coaches equipped with a compression brake even have a three stage engine brake. Since the "Jake" slows the coach by changing the exhaust valve opening timing, the different stages simple change the number of cylinders that are activated. For obvious reasons this can not be done with an exhaust brake.

A two stage "Jake Brake" will normally activate two cylinders on low setting and all six on high setting, and the three stage ones use 2, 4, or 6 cylinders. Because of cost, complexity, and efficiency compression brakes are rarely installed on engines smaller than 10 liters.

Gerald  

[Dick Simonis]

If I'm not mistaken...at least this is how I think mine behaves.....regardless of the gear that is selected when the Jake engages, mine is still 2nd, it doesn't actaully downslhift until it can do it safely without exceeding the 2300 rpm limit.  Most often mine seems to drop into 4th fairly quickly but doesn't downshift to 3rd or 2nd unti the speed really drops.  Regardless it's kinda like have the stern anchor drop off the pulpit once it downshifts.

I have not yet had it reprogrammed but am mulling it over.  For the short term I just move the switch back and forth between low and high.

[Joel Ashley]

I have to agree with Ken, because I used to drive at 55-60, staying in fifth, and over a long freeway trip I got just short of 10mpg on our as-yet broken in (9000 odometer miles back then) C9 CAT.  I figured the Economy Mode and CC combined with the old Oregon double nickles gave me the numbers.  This trip on higher posted speeds of Nevada, Utah, Wyoming, and Colorado freeways, I bumped up to 65 so the tranny would stay in sixth, and only kick back to fifth at 57 mph, and I wouldn't impede anyone.  Surprise, I still am looking at almost 10mpg with 12000 odometer miles.  Getting into sixth allowed a higher speed with the same mileage, obviously, so hanging to 55-60 was no advantage as it might be in a car.  The coach, a less weight-endowed 37 footer pushed with 400 horses, negotiates hills with ease, and downhill the CC comes off as I keep my left hand over the exhaust brake, flipping the switch as needed.

Reprogramming to a lower 6th gear speed might improve it some, but Ken's experience re. the lower gears being affected tells me the conversion ain't worth it.  I let the Allison do most of the decision making, and only manually shift to make a quicker pass.  Afterall, I can't scream too loud over 9-10mpg loaded and towing.

Joel  

[Jeff Watt]

Joel, Gerald,

Your right about the max HP and torque and as Gerald points out, off the line there isn't a lot of turbo boost. As I said, once this beast is moving, there isn't a lot of problem keeping up with just about anything. Returning from Texas in March with no cruise control, I had to keep watching my speed as it would easily creep up past my normal comfort zone, i.e 60-65mph.

I haven't done the intake upgrade yet and I may look into doing so.

Jeff

[Ken Sair]

Well, after some 260 miles in the rolling hills of NC and VA I have some additional info.

First of all.  I had a 2003 HR Endeavor 330 cummuns/allison 3000.  A sweet setup and it could get into 6th around 57/58 mph. I just assumed the new 2007 would also. Silly me. It would not shift into 6th until 63 MPH. As I set the CC to 62, every overpass/slight upgrade would cause a downshift to 5th.  I would then have to accelerate slightly to 63, get into 6th and back off the throttle. More of an annoyance than anything.  Anyway I asked Monaco why the higher speed to get into 6th and the reply was, after extensive testing they felt that was best, too bad.  Anyway, another CAL was available and I changed it.  For the past 5 years I have just been shifting manually with the arrow buttons.  Now, my bride is going to be doing some of the piloting.  She wants no part of shifting, so back it goes.

Over 70,000 miles there has been little if any change in MPG.  I check my mileage in 10,000 increments. The lowest was 7.7 (brand new) and the highest 8.24.  Over 70,000 I am averaging 7.94 mpg. Hope that clears up any misgivings.  I gained something, 6th at 57 mph but lost re: to quick into 4th-5th gears.

Now, the exhaust brake. Traveled from Gaffney SC to Lynchburg VA. Lots and lots of rolling moderate hills. Almost every activation of the EB went right to 4th gear. Only twice did it downshift to 5th and I found that gear to not provide enough braking, particulary at higher speeds (65-70) when I didnt want to exceed speed limits on downhills. So I am going with 4th for now.  Especially since we spend most of our time in the West.  2 is just annoying.

Thanks for all the help and advice.

Ken 2007 Contessa