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daveb1256 · 04-24-2021, 11:39 AM

I am hoping Smitty or Brian or others of you that are knowledgeable will weigh in on this. I have an 06 Intrigue 45' with a C-13 Cat 525. Cat's owners manual says that something slightly north of 2100 is max RPM. I bought my coach used and the first time driving it in the mountains and engaging the Jake, I was surprised to see the control panel for my Allison 4000 immediately changing the selected gear from 6 to 3. Sure enough, it decelerated quickly shifting down from 6th to 5th, then 5th to 4th each with an RPM increase of about 300 RPM. But whoa, when the RPMs fell below 1800 in 4th, it downshifted to 3rd and the tach spiked to 2400 RPMs with the engine screaming. Something is not right here.

Last summer with pure dumb luck I met Dave Atherton for the first time at the dog park while walking our dogs. Dave is a retired 42 year CAT technician and I ended up engaging him to run a complete diagnostic (including ECM programming) for what I considered a very reasonable fee. I asked Dave about my overspeed concerns when the Jake downshifts to 3rd. Dave assured me that the engine would not downshift if it would cause an overspeed. He should know. As a result of his diagnostic baseline report my engine in 105K miles had never thrown a fault code or had an overspeed event. I relaxed a little.

Recently we attended a rally in Ariz that included some mountain driving getting there, and I was once again reminded of the unnatural feeling when the downshift from 4th to 3rd created a screaming engine. As luck would have it, Eric Oldstrom hosted one of our sessions at the rally. When I asked Eric about this 3rd gear selection on my Allison, he replied that CC probably programmed this setting at their factory, but it was changeable through programning. Later that afternoon, I called W W Williams in Phoenix, and the next morning they reprogrammed the transmission to shift to 5th instead. The drive home through the Colorado mountains was much more relaxed as I was able to select the gear based on the speed and grade. My coach turns about 1500 RPM in 5th at 65 mph so the downshift from 6th to 5th is hardly noticeable. On the 7% downgrade for 12 miles, 4th gear, 2nd position on the Jake held the coach at 1700 rpm at 49 mph without ever touching the brakes. Never did need 3rd gear.

As a commercial tour bus operator for nearly 30 years, I have many hundreds of thousands of miles on Prevost Coaches with Allison 4000 transmissions mated to Detroit Series 60s and 8V-92s. None of them ever selected a transmission gear when the Jake was activated, and for good reason. An inexperienced operator who uses a Jake in wet or slippery conditions can get in big trouble in a hurry, especially if it downshifts thru several lower gears.

Anyone have any idea what logic CC had in mind when mandating a downshift to 3rd? Anyone else ever had this concern?

Smitty77 · 04-24-2021, 12:32 PM

Hi Dave - I'll speculate a bit here

!

Many coach owner's are 'get in and drive' kind of owner's, not digging too deeply into how everything works between the engine and transmission, and along with that the Jake. Many don't manually downshift for hill climbs, the just let the engine and trans ECM's handle things.

As a result of this, I speculate CC had lower default transmission gears chosen when the Jake is activated.

I'm personally not familiar with which gear the C-13/4000 is defaulted to by CC. And as you know from doing so, possibly a previous owner may have changed to a lower gear from the default(?). Other CC C-13 owners will chime in to confirm what Default is.

On RPM's, at least for Cummins ISL's, two different Redline RPM's were provided. The Jake Compression RPM was higher about about 300RPM's, then the under power/non Jake RPM. So your RPM's your seeing with Jake activate are probably fine. A call to CAT can give you the two Redline RPM's, and heck, may not be different like the ISL was...

And as noted, when working properly, the CAT/Allison ECM's - will not let you hurt the engine. They'll upshift if needed, to keep under max RPM's while Jake mode.

And I'm like you, with our ISL, I changed the Default gear for Jake activation to 5th. And then manually controlled downshifting as I felt was appropriate. On our ISX, I had the gear changed to 6th, because it like the C-13 - has just a tad more Braking HP then the 8.9 ISL's did

! So far I'm fine with 6th gear being my default, and I usually use Stage 2 to start with. Really like this combo so far on the few (Not many miles under our seat in this coach yet, but hope to add some this year!), as I can set the Cruise to say 65MPH, and when it is 3MPH over (The setting I chose.), Jake will activate and ease us back down to 65MPH. Really useful in rolling long interstate gradual grades/hills. I use I80 thru Wyoming as example, where this combo in our ISL coach, really shined.

Travel safe, and enjoy your coach,
Smitty

wolfe10 · 04-24-2021, 12:51 PM

Absolutely, the Allison ECU can be programmed for any "pre-select gear" for engine braking.

Like you I wanted control, not the Allison so like you I had 5th gear programmed. Easy to use the down arrows to select lower gears if desired.

You might call Caterpillar Corp with your engine SN: 877 777-3126.

There are several important numbers for any engine:

Max torque RPM
Max HP RPM
Max/governed RPM
And, of import to this conversation: Max no load RPM (i.e. engine not fueling/in overrun condition).

The last number is always higher than the max "while working" number which DOES make sense.

Yes, Dave is a treasure.

daveb1256 · 04-24-2021, 01:01 PM

Smitty, Thanks so much for your response and input! I suspect your speculation about CC's logic is correct. Your comment about using cruise control on rolling hill country with the Jake engaged to maintain a steady speed is interesting. On my coach, the Jake will not engage if cruise control is on. Like you say, controlling your roll downhill is a nice feature if can be done with cruise control engaged. Do you suppose this is also a programable item?

Jean n Steve · 04-24-2021, 07:02 PM

Dave, I want to say 2100 is my redline too, and 2400 would make me curl up in a ball in the seat. Wow.
My manuals all state that with cruise on, Jake doesn't work. Whether that's mechanically fixed or not is a good question.

Steve

BrianGlenn · 04-24-2021, 08:48 PM

I suspect CC did configure the power train in each coach to parameters able to be programmed and "standardized" across the CC models and lines. They would be limited to settings available to be programmed in each power train/application.

One can imagine the engineers or techs scratching their heads on how to "standardize" when a configuration available changed each time a new power train was introduced or modified by a supplier - ie Cummins or Cat, and Allison where applicable.

I can talk to my Cummins 400ISL, CM850 which has Common rail, VGT,
and Allison 3000MH, as I have collected information and knowledge specific to my coach. That said I have delved into many ECM programming/flash/custom tuning/troubleshooting over the last 20 years. Started with a 1987 Monte Carlo Aerocoupe that I balanced and printed the engine, and then could not get it to run right - but I digress.

Yes - downshift gear on deceleration can be programmed in the ECM, plus whether or not engine brake is available on cruise control. My CM850 400ISL was programmed by CC to "Enable Cruise Control Activation" on engine brake (see picture 1). This feature description (picture 2) is from the ISLCM850 Insite Manual for this engine; it can be enabled or disabled.

I have not seen the ECM programming parameters set by CC for the C13, nor what is available to program into the ECM (from Cat) by CC. I have always "admired" the C13 (and 500ISM) and hope to own one some day. The wife and I are looking at Intriques, Magnas for our "full time" coach.

Hope this helps,

Take care,
Brian

Twolanes · 04-24-2021, 10:26 PM

I own a 2002 Magna with an Allison 4000, powered by a Cat C12. On my first trip home after purchase, I immediately noticed the over-revving (2100+) engine RPM downshift to 4th when the Jake was turned on to the 3rd stage. I didn’t like seeing my engine at that high RPM, way too close to redline. After researching a bit, I soon realized that an Allison shop could easily program the 4000 to shift into any gear I asked when the Jake was applied. I choose 6th, which allows me to “manually” downshift further as conditions require and RPM’s allow. After the re-program my engine RPM very rarely exceeds 1900. IMO, much improved down shifting and engine braking control without worry of over-revving our $$ engines. All other tranny functions are unaffected. $75 at the local Allison shop. Took the tech a bit to figure out how it was done, but he got it done. Highly recommend this simple re-program. BTW; this issue has been covered by others on IRV2.

daveb1256 · 04-25-2021, 04:07 PM

Thank you all for your comments and info! Brian, I will see if mine can be programmed to use cruise and the jake at the same time if the speed exceeds the cruise speed setting. Smitty now you have me thinking that perhaps I already have that feature... I know that the jake will not engage when my speed is below the speed selected for cruise, but I don't know if I ever tried to see if the jake would engage when my speed exceeded my selected setting. Guess I never thought about that. Learn something new every day!