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Old 04-07-2015, 08:59 PM   #15
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OK. I called the cat RV hotline and not much help from him. He says call a Cat dealer, soooos I called one. John wasn't To informant either. Last words were to call a Detriot dealer and see if I have a software issue with the trans and engine combo. So thats where I am at. Grrrs LOL.
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Old 04-07-2015, 09:18 PM   #16
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Syl, do a google search for Cat C12 and Allison transmission. Some Beaver and Country Coaches with that combination (including mine) were built and they will over rev the engine if the default gear is set to 4th. DO NOT believe anyone that tells you the computer won't let it. For some reason these models fell through the cracks and the over rev limits were not set correctly. Find an authorized Allison dealer and have them set the default to 6th gear. It will downshift and work better for you. If it won't slow you down in the gear you are in just push the down arrow on the keypad until you find the one that works for you. I delivered brand new class 8 trucks for a living and figured out my moho was over revving on our first outing. Had the default gear reset to 6th and it's the best thing I did. Marty
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Old 04-08-2015, 09:46 AM   #17
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I recall a report in another engine braking thread where an engine was damaged from over-speeding. This was because the programming in the engine and transmission was not compatible, and the transmission shifted to a lower gear than was safe.
Ah yes, here's the poster who brought that up:

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DO NOT believe anyone that tells you the computer won't let it. For some reason these models fell through the cracks and the over rev limits were not set correctly. Find an authorized Allison dealer and have them set the default to 6th gear.
We started to discuss this in that other thread. Wouldn't it make more sense to have them correct the programming that lets the engine over-rev? By just setting the default to 6th gear, and manually downshifting, it still allows you to over-rev the engine if you don't do the downshifting just right. But if the programming were fixed to prevent the over-rev condition, then it wouldn't matter what the pre-select gear is, or what they operator did manually, the engine wouldn't over-rev in the first place.

To me, it sounds like you want to treat the symptoms rather than cure the disease. I would think the better route would be to fix the over-rev limits, not mask it by changing the pre-select gear.

If you're getting poked in the eye by the coffee spoon, doesn't it make more sense to take the spoon out of the cup, rather than tape padding over your eye?
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Old 04-08-2015, 03:31 PM   #18
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OK. I called the cat RV hotline and not much help from him. He says call a Cat dealer, soooos I called one. John wasn't To informant either. Last words were to call a Detriot dealer and see if I have a software issue with the trans and engine combo. So thats where I am at. Grrrs LOL.
Syl,
You didn't answer my question. At what speed is your tranny down shifting to 4th TOO SOON?
Scott
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Old 04-08-2015, 03:32 PM   #19
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Shapeshifter, think of it as if it were a manual transmission. The Jake would work in what ever gear it was in. If that wasn't enough, downshift. When those Allisons are installed in class 8 and 7 trucks the default gear is set at 6th. Trust me, I delivered them from the factory to dealers all over the US and Canada. I asked a motorhome salesman at an FMCA rally why RV manufacturers have the default gear set lower and this was his response "diesel motorhome owners don't know how to use a Jake or Pacbrake correctly so we just have it set that way". Remember, even if you have the default changed, the transmission still works correctly, if you slow down the trans downshifts as it should and then upshifts when you get back in the throttle. All I am saying is, as owners we need to be pro-active and know the limits of our motorhomes. Be it RPM or miles per hour, if you don't know the limit of something, you don't know you or it is doing something wrong. Say for instance, many times I have had people in motorhomes pass me going faster than 75mph. I know my tires are only rated for 75mph. Does the other guy know the rating of his? I know I can't trust a computer to not let me drive faster than the tire is rated for.
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Old 04-09-2015, 03:24 PM   #20
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Marty, you're missing my point. I don't care what gear you or anyone else chooses as their pre-select. What I'm concerned about is your recommendation to change the pre-select to mask a serious ECM/TCM programming error.

Your own words:

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For some reason these models fell through the cracks and the over rev limits were not set correctly.
First, get the shop to FIX THE PROBLEM and set the over rev limits correctly. Then go ahead and program whatever pre-select gear you want.

Changing the pre-select gear is a personal choice for a variety of reasons, but I feel strongly that masking an over-rev programming error is not a valid reason to change the pre-select.
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Old 04-09-2015, 05:17 PM   #21
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Shapeshifter, your are missing the REAL point! If the powers that be would just leave the default at the highest gear of the trans 6th for a 6 speed and 5th for a 5 speed or 4th for a 4speed we would not have to have this debate. Marty
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Old 04-09-2015, 05:41 PM   #22
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If the powers that be would just leave the default at the highest gear of the trans 6th for a 6 speed and 5th for a 5 speed or 4th for a 4speed we would not have to have this debate. Marty
Good try Marty! But ....... Only the driver's that use to drive big trucks understand what you are saying..........These Coach's drive lines were set up for those that never drove "Large Car's Mine stays in 6th and any other one I might acquire....will be re-programed also
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Old 04-09-2015, 05:45 PM   #23
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Shapeshifter, your are missing the REAL point!
Why don't you just get a manual transmission? It sounds like that is the only way you will be happy.


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Only the driver's that use to drive big trucks understand what you are saying
I understand the concept of shifting gears to maintain appropriate RPMs and manage power and speed. I understand the need to be aware of the vehicle's capabilities and limitations and how to manage it properly. I understand how different drivers could have different preferences. What I don't understand is how he can complain so bitterly about a programming error in certain coaches, and yet he refuses any suggestion about fixing the fault. It's as if he wants the fault to remain so he can justify his feelings about how all other coaches should be programmed, and therefore deny other driver's their preference because it's not what he feels is correct. That's not really the case, is it?
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Old 04-09-2015, 06:18 PM   #24
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Whats sad here is when I read in another section about a 600k Coach that the cruise control will not maintain set point with the use of the engine brake until it is 15-20 mph over the set point, then it comes on, downshifts, High rpms , quick slow down, up shift after getting way below set point, back to 6th........a viscous cycle, so most leave the engine brake off and use the brakes to maintain. If they would have it programed to remain in 6th, and the cruise control set up to maintain 3 mph over/under the set point..... their engine brake would work wonderful maintaining set point and then one could just select between the engine brake stage's according to how much braking power was needed, and maybe even have to hit the down arrow on the shifter keypad to 5th for more braking power............
I have asked a lot of questions on here about how the newer Coach's are setup.......and everyone has told the same story..........If they were to have the ECM & TCM set up and give it a try.........I think they would tell the same story, and find that they "Really" enjoy driving their Coach now. It sure is a cheap test to have done, The Cummins/Allison shop near me did not even charge me to set mine up the way I wanted. Yes, everyone has their thoughts...........sometimes change is good.
As far as max rpm's on any engine........I have no desire to play in that playground.............I did when I did not own the engine's........
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Old 04-09-2015, 08:27 PM   #25
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Shapeshifter, your are missing the REAL point! If the powers that be would just leave the default at the highest gear of the trans 6th for a 6 speed and 5th for a 5 speed or 4th for a 4speed we would not have to have this debate. Marty
Marty
In my case the "powers that be" knew what they were doing.

As built and/or programed 19 years, (140k miles), ago, mine automatically selects 2nd gear when the PacBrake is switched ON.

I certainly would not want mine to select 6th gear... because I certainly DO NOT want HAVE TO MANUALLY DOWNSHIFT my 6 speed AUTOMATIC Allison every time I want to take full advantage of my PacBrake.... (and then MANUALLY UPSHIFT when the PacBrake is not needed).

Mel
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Old 04-09-2015, 11:57 PM   #26
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Mel, my coach is set up the same way, and that's the way I want it. I use the Jake to slow us down when we come to a stop, and the Jake does most of the work almost to a stop. When we get a newer coach I will have that reprogrammed with second as a target gear as well. It's worked quite well so far.
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Old 04-10-2015, 07:10 AM   #27
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Marty
In my case the "powers that be" knew what they were doing.

As built and/or programed 19 years, (140k miles), ago, mine automatically selects 2nd gear when the PacBrake is switched ON.

I certainly would not want mine to select 6th gear... because I certainly DO NOT want HAVE TO MANUALLY DOWNSHIFT my 6 speed AUTOMATIC Allison every time I want to take full advantage of my PacBrake.... (and then MANUALLY UPSHIFT when the PacBrake is not needed).

BTW, not only does the selection of 2nd gear make the shifting of my Allison completely automatic when ever I use the PackBrake...I have added a "BrakeSwitch relay" which also makes the operation of my PacBrake AUTOMATIC.

Mel
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Old 04-10-2015, 07:18 AM   #28
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An Allison Transmission is a LOT smarter than 99% of the people using it in a vehicle.

For those people who have no clue as to how one works may I suggest that you spend an evening with the manual, you might learn something.

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