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Full Version: Jake Brake Programming
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Most Jakes on new Wanderlodge(s) were programmed at the factory to select 4th gear initially and then progressively select 3rd then 2nd and then deactivate when travel speed dropped below 15 mph.

Many owners disliked that programming as it removed the Jake’s ability to function above a travel speed so fast that 4th gear would over rev the engine. Consequently, they had their Jake Brake re-programmed to select 5th gear first then progressively shift to the next lower gear as travel speeds decreased to allow downshifting the transmission without over revving the engine.

My previous LXi’s Jake Brake was set at the factory and was never changed. A travel speed over 65 mph locked out the Jake until travel speeds were reduced below that point. So, I made it a practice to stay below 60 mph on downgrades to prevent having to over use the chassis brakes to slow the bus down.

Most Wanderlodges were equipped with a 2 or 3 stage Jake. Both LXi(s) I have owned were equipped with a 3 stage Jake. This makes it great for selecting the perfect stage for the downgrade that would allow the Jake to hold the bus at a constant speed. By manipulating the Jake’s stage, I could travel the length of the downgrade without ever touching the chassis brakes.

Now I find that I, evidentially, have a hybrid program on my present (new to me) LXi. The Jake is programmed to select 4th gear initially but to my surprise the transmission shifts to 5th gear initially if my travel speed is too high for the Jake to shift the transmission directly to 4th gear. I use a Silverleaf engine monitoring system that displays the selected gear and the actual gear. The Jake selected gear displays a 4th gear but the actual gear shifts to 5th until travel speed is reduced to allow shifting to 4th and so on.

This program is the best of both worlds. It allows the Jake to activate at a higher speed which is helpful if I’m traveling at a higher speed than 65 rather than waiting for the speed to be reduced enough to initially shift to 4th gear. On the other hand, if I’m traveling below 65 mph, I get the benefit of faster reduction of speed when the Jake immediately shifts to 4th gear rather than it having to select 5th first before selecting 4th.

Does anyone else have a Jake Brake programmed this way?
That is how mine works. I do not like the shift to fourth gear most times. When I am descending mountain grades the engine brake operating in 5th is often enough to control the speed. Once it slows to a speed that the transmission shifts to 4th it slows the coach more than I want. I have been planning on getting the transmission ecm reprogrammed to stay in 5th initially. You can always manually select 4th gear when you want more braking earlier.
I've found that turning the fan override on is another way to fine tune the jake brake stopping power. The fan on the LXi can sink another 40 HP of stopping power in addition to the 350 HP of stopping power offered by the jake. In some cases I find that 4th slows me down too much and 5th not enough, while 5th with the fan override on is just right.

Chuck, my LXI works as you describe. If the rpm's are too high for the pre-selected 4th gear to be used, the jake will use 5th and it will operate at speeds above 65 mph. But, when the transmission decides that rpm's are sufficiently low for 4th gear to be engaged the downshift causes the engine to over-rev to 2350 rpm. For this reason I had my transmission programmed to pre-select 5th.

With the new programming the transmission uses a new set of rpm setpoints when downshifting; the chosen rpm setpoints are well below max braking power for each gear. The solution is to manually push the down arrow to select lower gears at rpm's that provide full braking power. The challenge then is remembering to hit the up arrow to allow use of all 6 gears when on the flats. A short cut to depressing the up arrow multiple times is to hit 'D' once - this has the effect of instantly selecting 6th as the max allowable gear.
My '95 also goes to 5th first before getting to 4th although the transmission display shows 4th. Works great.
x3!Wink Curious, are you running DDEC III or IV? Just trying to find when Bluebird did the cut over.
(08-21-2013 10:05)pgchin Wrote: [ -> ]Chuck,
x3!Wink Curious, are you running DDEC III or IV? Just trying to find when Bluebird did the cut over.

Hi Pete, (Here's What I Think) After research!!

DDEC III. I'm not sure when the cut over was but I'd bet David knows...... I think it's DDIII through 2003

This question is directed at the Prevost owners.

How did your specific converter (or Prevost, if that's who did it) program your Jake Brake? Specifically, when the Jake activates does it downshift the tranny to 4th, 5th, or does it stay in 6th?

I know how BB did it and was just wondering about Prevost.

Prevost did it the same way as BB; that is, the standard approach is to preselect 4th gear. A lot of folks in the Prevost world have had the preselect changed from fourth to fifth. I don't have a Jacob brake on my Vantare; I have a transmission retarder, but it's the same. The preselect is fourth.
Thanks for the info, David. My parents owned a '97 Liberty which I drove on a number of occasions. However, I just can't seem to remember how their jake was programmed. I do remember using it and don't recall thinking that it was too harsh upon activating, which made me wonder if it was set to 6th. That's why I was curious about how other Prevosts were programmed.

Last year I had my BB programmed from 4th to 5th. It made a big difference, and I've driven nearly 20k miles since then, but I still couldn't get used to the high engine revs when downshifting to 5th at highway speed. I just recently had it changed to 6th and couldn't be happier. Now she's smooth as butter on the highway off ramps or at highway speeds in general (and 5th gear is only a button away if I need it).

I also modified the enable switch which consisted of replacing the on/off switch with a on/off/on switch and running an extra wire. It took all of about 10 minutes to perform the mod. Now, depending on the position of the switch, the jake will activate either at 0% throttle position (as originally designed) or upon depressing the brake pedal (and will stay active until throttle is applied).

I'm very happy with the changes this far. The next thing on my list is to stop the brake lights from activating with the jake.
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