[Marshall]

It sounds like the Jake is not kicking in. A Detroit dealer can trouble shoot the problem and you can have your coach set up for a downshift to any gear you choose.

It could be any number of issues, including a throttle position sensor not detecting when your foot is off the accelerator.

[Corey]

Jon,

Thanks for your quick reply. The jake definitely kicks on. You can feel the braking and the brake lights come on. Sounds like its just a programming issue with DD.

I’ll manually downshift for awhile and determine what gear selection I prefer.

Thanks again

[John]

My preference differs from others, but my retarder (similar in use to a Jake) is set to drop a gear when engaged. After that I manually downshift to stay within a good performance range of RPMs while avoiding an over revving condition.

[Jim]

My 06 Royale drops to 4th immediately, so I often have to brake a bit to get some speed off before engaging Jake. Otherwise RPM might jump higher than I like. Maybe 5th would be better and manually downshift from there.

[Fred F.]

It’s an Allison Transmission programming change. Any Allison shop can do it.

[Corey]

Great Infomation! I’ll look for an Allison shop. I’m betting there is one near me in Nashville…..

[Corey]

Marshall,

Clarke power In Nashville.

[Corey]

Mine is programmed to 4 th gear, but over 60 or so it will drop to 5th gear then 4th when RPM’s are rite, Allison smart trans should not allow engine to over rev. On my last coach U320 Foretravel it was Programmed to 5th gear so when jake went on it hit 5th then I had to manually down shift then, but it an emergency stop it’s better not to think about downshifting. When I 1st bought the Bus I was going to have trans reprogrammed, but a couple of people on the forum said to try it for a while, you will get use to it.

[Roscoeapproved]

A trip to DD about 3000 bucks, have it down shift to 2 have high RPM set to 2350 DD won’t set it any higher and won’t shift if above 2350 RPM.

---

Jeff and Lindsay

91 Marathon XL

[Dick]

The downshift should not put the engine in an RPM over the stated max RPM of 2100, but if the grade is steep and the coach is accelerating when the Allison gears down it could push the RPMs. That is why with the Jake or retarder I manage the coach energy using whatever is appropriate to maintain target speeds, control temps if required and prevent over revving.

I am ALWAYS in my target gear and at my target speed before the downhill portion so I am not relying on the coach systems to do my job. On modest grades I just let the retarder handle the downshift and I manage the retarding strength with the stick. I usually leave the stick in the zero position, retarder on, so I have immediate retarding force in the event of needed braking, but on the downhills I control speed, usually by selecting the 2nd or third position with the retarder stick.

[Davy]

Dick,

Is the transmission max RPM limit something that can be changed by Detroit Diesel? Or is it always set at 2350?

[Archived]

Detroit lists 2100 as max RPM. Drive your coach as you wish, but that is what the book says.

[rafael]

OK. Same question for 2100 max RPM. Can Detroit Diesel set this configuration? Or is it fixed at some other RPM?

[Marshall]

Here we go again with 2nd gear jake selection. Just keep in mind, if 2nd gear is programmed and your on a steep down hill grade, when the speed parameters are met, it will abruptly select 2nd gear and you will see rpm’s exceed the max, so be ready with the brake. Regardless what max rpm was programmed, downhill momentum and weight will push the rpm’s up.

For those that want to try it, while at highway speed just let off the throttle with jake on and manually select 2nd gear. When the speed bleeds down and is within the parameters it will down shift to 2nd. Let us know how you feel about that.

I had an XL that was programmed to 2nd when I bought it, thought the drive train was going to fail the shift was so harsh. I had it programmed for 6th so it’s active all the time, that’s what manual gear selection is for.

[Archived]

Your engine is set for 2100 in gear max RPM, but you can push it. For example point the bus downhill in 4th and if the hill is steep enough the bus can pick up speed and push it past 2100.

It is up to you as a driver to drive your coach however you see fit and most of the time the coach systems and ECMs protect the coach from you, but it is still possible to exceed limits.

I think out of gear it is governed for somewhere around 2300 or 2400.