Jake brake not working

[Ramrod]

I have a 2004 CC Intrigue w/ 400 ISL. High or low on the switch the Jake comes on in low mode and trans downshifts to 4th gear. That's all I get.
Is this a Cummins issue or an Allison issue??
Thanks

Tom

[Steve Ownby]

The Jake brake function is a Cummins issue and the ECM communicates with the Allison transmission to select 4th, 3rd or 2nd when the Jake is engaged. How do you know the Jake is in low mode regardless of the selector switch position?

[Ramrod]

the high and low switch produces the same amount of braking. The trans downshifts to 4th then stop downshifting. That cause me to use the brakes to slow the coach. This is my first coach with a jake. previuos coaches were Cat engines with exhaust brakes. I think they should act similar.??

[Route 66]

They are similar, but a Jake brake is much more effective.

My Jake brake on high was like throwing an anchor out...........sometimes too much braking and I would switch it to low.

You need a Cummins shop that has the ability to access the Cummins ECM software.

[Steve Ownby]

Tom,

It's pretty unusual for 4th to be the gear selected when the Jake is active as 4th is the highest gear that produces very much retard effect. I would visit a Cummins shop and have them set the downshift to 3rd or even 2nd. When the Jake is activated you will see this gear selection in in the Allison selector display. The Allison will then downshift as speed and rpm drop until you reach the selected gear. The Allison will not allow a shift that would cause an engine over rev. If the selection is set to 4th then no further downshift will occur due to the action of the Jake. That also may be why you can't tell any difference in the "high/low" switch. If you have a window over the exhaust pipe, position someone at that window on a long down grade and turn on the Jake. Toggle the switch between high and low. There is a distinct difference in the exhaust sound between high and low.

[a1elect]

From past experiance i know that if the gas pedal is not showing 0 input the jake brake will not operate. Found a worn bracket one time on an older rv we used to own.

[Smitty77]

On our 04 Allure with ISL 370, the Low Jake would kick in, and switching to High was also not making a difference. As part of our purchase agreement, this was repaired by Cummins for us, with the cost covered by the seller.

In our case, Cummins had to go under the valve cover, and reset a mechanical setting. If I understood it right, the setting was not correct out of the factory, so the full compression of the second set of 3 pistons was not kicking in. The valves were not full closing.

Reading up on this, I recall also a group of 03-04 (I think) Country Coaches that had a pin problem, between the Allison and ISL.

I'd suggest a Cummins shop that is also a certified Allison repair too, and let them run diagnostics.

Our repair, made a 'seat of the pants' difference.

Best of luck, and sure would enjoy you closing the loop and letting us know what you find out.

Smitty