Jake Brake

[Edward Buker]

Richard,

You have a C12 in a Marquis. There are other coaches in the Beaver line that do not. You do have a 3 position switch for the Jake. The low setting uses 3 cylinders for compression braking and high uses all 6, the center position is off.

Larry,

Your coach may already be programmed to go to 5th or 6th gear and not 4th gear when the Jake is applied. I was in the Allison Program on my coach with the tech last week and under compression brake 4th gear was listed. He deleted that listing (5th was an option in the drop down menu) and now I can apply the Jake brake in any gear and the transmission will do its thing downshifting within the whole range of available gearing, and not go to 4th gear regardless of speed. I have no doubt that the folks at the seminars said that the ECUs and Automatic transmissions will protect the engine and not allow over revving. I also know from three years of driving this coach and having witnessed what Marty has inputed here that my coach has never seen 5th or 6th gear regardless of speed with the Jake engaged until it was reprogrammed last week.

Seems like there are a lot of perspectives on this issue and that is fine, everyone has to look at a problem for themselves and decide what is relavent to them. From a safety standpoint and an engine preservation point of view each owner should run their own tests and see what gear is selected on the "Drive" screen (upper right) on the monitor when the Jake is engaged. You can turn the Jake on/off and incrementally increase your speed set point as a test. When you engage the Jake, see if the transmission goes to 4th gear and what RPM shows on the tach. Increase your speed 3mph starting around 57MPH and repeat applying the Jake and note the RPM. When and if you get to 2300RPM or higher at some speed and the Allison keeps selecting 4th gear when the Jake is applied, then I would stop at that point and look to have the Allison reprogrammed. A simple test on your own coach resolves this issue for you...

Later Ed

[Joel Weiss]

I have not yet experimented in changing the gears.  My transmission red display (to the left of drivers seat) reads 6 all the time.  All I've ever done was change it to economy mode at times.

The "arrow" keys on the transmission pad work just like the "manually shiftable" automatic transmissions found in many cars.  You don't need to use them most of the time, but, for example, when I am climbing a steep hill I will use the "down" key to force the Allison to stay in 4th gear so it doesn't "hunt" between 4th and 5th.  Not only is "hunting" annoying because of the jolts it produces, it also causes transmission wear.  On very severe downhill runs I have occasionally taken the transmission down to 3rd to keep the speed as low as needed.  Usually running in 4th with the Jake is sufficient to maintain a safe speed, but we have been down some hills where even more braking is needed and this provides it without having to use the service brakes.  When you do use the arrow keys the "highest allowed gear" will be displayed on the keypad and on the Silverleaf.

Don't feel badly about not having read all the stuff that comes with the coach; I was new at this 18 months ago and felt overwhelmed.   This forum is an excellent source of advice, most of it good.    

Joel Weiss

[Joel Weiss]

For those who care, this is the post from the individual who reported having blown his C12 and I think most of posts on this forum and others relate to his experience:  http://community.fmca.com/topic/3791-blown-c12-the-rest-of-the-story/

If my coach was geared the way Ed Buker's is I would probably have the Allison settings changed.  However, since I can engage the Jake at 65 and be below 2100 it doesn't pose a significant issue for me.  

FWIW Cat did make a version of the C12 for marine use that was rated at 2300 rpm; I wonder what the difference was:  http://marine.cat.com/cat-C12

BTW, with the latest Silverleaf firmware update I now have 6 functions in a readable fixed display on my drive screen.  Top of the list is the tach; now I have a readable tach that I can used to observe engine behavior when using the Jake.

[Dick Simonis]

For those who care, this is the post from the individual who reported having blown his C12 and I think most of posts on this forum and others relate to his experience:  http://community.fmca.com/topic/3791-blown-c12-the-rest-of-the-story/

If my coach was geared the way Ed Buker's is I would probably have the Allison settings changed.  However, since I can engage the Jake at 65 and be below 2100 it doesn't pose a significant issue for me.  

FWIW Cat did make a version of the C12 for marine use that was rated at 2300 rpm; I wonder what the difference was:  http://marine.cat.com/cat-C12

BTW, with the latest Silverleaf firmware update I now have 6 functions in a readable fixed display on my drive screen.  Top of the list is the tach; now I have a readable tach that I can used to observe engine behavior when using the Jake.

Joel, that sounds about right.  At 65 in 6th, engaging Jake drops me to 5th (2-5 displayed on Siiverleaf) that progressively drops me through the gear with each gear change bringing the rpm up to 2300.  Like you I have found that manually selecting 4th for hilly conditions works very well and max speed in 4th seems to be about 62 while 5th will go faster than I care to drive.

This has been a good thread and has gottem me thinking about reprogramming....probably to 3rd.  But than again I really did like the preprogamed 2nd when I came down 20 from Bend as I was too busy dodging tree branchs to bother looking for the shift pad to shift to 2nd....and I spent fair amount of time there.  Think steep downgrade, 25 mph posted corners with a big bump on the approach....I was a busy Beaver.

[Edward Buker]

Dick,

I don't think you mean reprogramming to third, that term would typically mean changing the settings in the Allison ECU to go to third gear whenever the Jake is engaged. I think you mean manually selecting or preselecting second or third using the shift pad arrows as you see fit.....

Later Ed

[Dick Simonis]

Dick,

I don't think you mean reprogramming to third, that term would typically mean changing the settings in the Allison ECU to go to third gear whenever the Jake is engaged. I think you mean manually selecting or preselecting second or third using the shift pad arrows as you see fit.....

Later Ed

No, I really did mean for the Jake to select 3rd, right now it preselects 2nd and downshtifts accordingly.  2nd is OK and, like I said, I've found useful but 3rd might be better over a wider variety of grades.  I select the highest gear I wish used and let the Jake select the lowest.  So far that has worked good but I do admit to inexperience and still finding my comfort zone.  The shift pad location still requires that I divert my attention from driving to look for the selector and on twisty downhills that is bothersome...lot easier to let the Jack do some of my thinking and toggle back and forth between hi and low.