Community Forums

wolfe10 · 05-03-2018, 03:21 PM

The "gear toward which the Allison shifts when the engine brake is applied is programmed into the ALLISON ECU. Yes, it can be changed in about 10 minutes by any Allison dealer (or dealer with Allison computer) to anything you want. 5th was always my choice, but I don't mind using the down arrow for lower choices.

kraig · 05-03-2018, 11:27 PM

As I remember WRV programmed all the exhaust brakes for 4th and 5 th gear only. I went to the Allison dealer and reprogrammed for 3,4,5,6. I have a heavy coach and a heavy toad. I only use the high side and works great for me. Hardly use my service brake at all. Since the switch on mine the indicator light does not function, I added green light to show when it is off.

bcruzen · 05-04-2018, 05:31 PM

I like the idea of having the transmission gear program changed. I hate going down a hill and having the engine rev to 2500 rpms when it drops to 4th gear. I think i would rather have it stay in 6th and give me the option to hit the down arrow for more braking power if needed. Don't need a piston flying through my bed.

Another thing to note, if you have not had an overhead done on your ISL, think about it soon. There's a weakness in a retaining clip in the valve train for the engine brakes. I have two fire engines ('05 models) with ISL engines. Both of them had this problem and the mechanic, whom I know, said it was perfect timing as several of them were ready to brake off and cause a lot of problems. My engine did not have this issue. Maybe a '05 Cummins issue?

Cinequip · 05-04-2018, 11:01 PM

I am curious, Kraig, with your ECU programmed for 3,4,5,6, what gear is chosen when you lift your foot off the gas? I have long been irritated that mine chooses 4th, and often revs the engine too high. I’d prefer to have the tranny always choose 5th, but allow me to select a lower gear manually. Cruise control does a better job with engine brake. With cruise on, 5th gear is always chosen to slow down, unless the hill is so steep that 4th is required for greater slowing. Out of cruise, it’s always 4th.

Anybody know what the options are for this with Allison/Cummins?

To the thread topic: there is a clear difference between hi and lo engine brake on my coach. High setting will gradually slow me down on a steep hill, whilst low mode will gradually allow me to speed up.

wolfe10 · 05-05-2018, 06:52 AM

There is only a single "pre-select gear" when engine brake is engaged.

So, for example if it is 2nd, the Allison shift pad will instantly show "2". NO, that does not mean the transmission shifts from 6th to 2nd at 60 MPH.

It means "as soon as it is safe to do so without over reving the engine, it will downshift until it reaches 2nd gear.

IMO, if you don't mind using the shift arrows, 5th is an excellent choice. Can't imagine where you would want 6th with the engine brake on (look at your speed/RPM curve).

But, for example headed west on I 40 into Albuquerque, 5th with engine brake on low alternating with high is perfect. A real pain for it to try for 4th, then have to release it, re-engage ......

Cinequip · 05-05-2018, 10:04 AM

Wolfe, do you know if there is a max RPM setting in the ECU? Mine seems to be unlimited. I’d like to have it limited to 2300 rpm or so. It would be fantastic to have 5th selected first, and then progressively move to lower gears as the max rpm threshold is reached at the enter point for that next lowest gear.

wolfe10 · 05-05-2018, 02:02 PM

Yes, an Allison dealer should be able to plug in and tell you the max programmed RPM. There WILL be one.

3x5 · 05-09-2018, 12:48 PM

Hi All,
I took the rig into Cummins to check the Jake brake. They said it is fine. The wiring and stuff checked out. Then the tech took it on a very short test drive on a flat street and listened to the hi and lo. He said since he could hear a difference in them, the Jake is ok. I have some doubts, but I will find out over time.
I guess I was expecting more from it, like shifting to another gear. I tried testing it on a flat highway, dropping from 60 mph to 45 or 50. I admit there was a difference, but not nearly what I expected.
But, they also found that my manifolds were warped and leaking pretty badly. I got them replaced, and I think that seems to have increased the braking power a lot, though not the difference between the two. I'm not sure yet, because I had to drive straight over to another shop where I had an appointment to get some woodwork done, and there are not any hills around here.
Thanks for the help.

John

wolfe10 · 05-09-2018, 03:16 PM

John,

With an engine compression brake (aka Jake brake) the exhaust manifold would have nothing to do with brake function.

With an exhaust brake-- it absolutely would.

But, if the leak was bad enough, it could affect power, as the some exhaust could escape before "powering" the turbo.

Jim A · 05-10-2018, 09:30 AM

No change in gear selection with high and low on Jake brake. Same gear (4th on mine), just more compression.

3x5 · 05-12-2018, 05:36 PM

Quote:

Originally Posted by wolfe10

John,

With an engine compression brake (aka Jake brake) the exhaust manifold would have nothing to do with brake function.

With an exhaust brake-- it absolutely would.

But, if the leak was bad enough, it could affect power, as the some exhaust could escape before "powering" the turbo.

Brett,

Makes good sense. Thanks.

We have been sitting since we got the work done, and it doesn't look like we will get a chance to drive for a long time. I will have to be patient until I can really check it out.

whalepirot · 07-15-2018, 05:37 PM

Appreciate the education on the jake. This is my first experience owning (400ISL w/ 2 stage) and I just wonder if I can over use it!

It must have been programming differences from a jake demonstrated to me on a test drive of a HR 36'. That one was effective to a near stop.

wolfe10 · 07-15-2018, 06:08 PM

Quote:

Originally Posted by whalepirot

It must have been programming differences from a jake demonstrated to me on a test drive of a HR 36'. That one was effective to a near stop.

Yes, the Allison ECU can be programmed for any "pre-select gear" when the engine brake is engaged.

2nd would be great when coming to a stop, but a pain in highway down grades. You can certainly use the down arrow to select a lower gear if you desire. You could also have an Allison dealer reprogram the ECU if you feel that better meets your needs (it would not be my choice).

Wil Rathke · 07-16-2018, 08:10 AM

I have found that the Jake Brake will shift to 4th speed regardless of Hi or Lo mode unless the road speed would overspeed the engine and then it shifts to 5th.