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Tennessee mountains and jake brake driving

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Richard Cooper:
Tomorrow I'm heading out of Nashville to Chattanooga, Tennessee on I-24 East and have to go over Mounteagle and down a 5% grade over about 5 miles.

Should I adjust the Allison transmission gear to 1 or 2 or 3 besides engaging the full jake brake?  I have in my 2001 Beaver Marquis the Meritor ADB Series Dual air disc brake system w/auto slack adjusters.

What if the jake brake were to fail --- besides pressing the foot pedal brake would I slow the motor coach changing the gears on the Allison transmission settings?  Normally it just shows "6", but automatically adjusts for climbing hills.  I'm talking about going down the hill.

Joel Weiss:
Going down hills I find the 4th gear default on my Jake to be satisfactory on all but the steepest grades.  The 5% grade you mentioned will be fine probably with either half or full Jake.  For any particular hill, what I do is decide which Jake setting will permit me to descend without speeding up at my desired speed; you can never have "too much Jake" but it may actually provide so much braking that you have to press on the accelerator occasionally.

On the very steepest grades (~>7%) I will slow my speed to <45 mph and manually shift the Allison to 3rd. I've only had to do this a couple of times on a few long, steep grades.  If you didn't have a Jake you would do the same thing, manually take the transmission down to 3rd or 4th.

Richard Cooper:
That is very good info and I thank you.  

I know this question must seem elementary to most everyone reading, but to me it is a new step in my less than 1 year experiences driving a motor coach.

JimCasazze:
Be careful of engine RPM and do not allow engine to exceed 2100.  Brake if you must.  Speed at that RPM will vary by coach but on our patriot thunder c12 it is about 63 mph.  I try nit to engage Jake over 60 to be safe.  Low Jake works on up to about 4% with a toad and no toad brakes.  Full Jake holds me on 6 to 7%.  Over that I slow way down and/or use medium brake pressure fo 2-3 seconds ar a time.  This has worked well for us up to one road that was 11% that I should have avoided.

Edward Buker:
Joel has given you some good insight. If you find yourself cresting a climb and there is a downhill grade that you are approaching prepare yourself by getting the speed down a bit at the end of the climb, maybe to the 50 -55mph range if you are going faster. If secondary road and steep, even slower of course. This prep gives you a little more time before any downhill acceleration to set the jake on at the appropriate time and gear. 4th gear and 50 to 55mph is a good match on the interstate most of the time. Joel points out that 7% slopes or steeper may warrant third gear and a slower speed. Rather than throttle like Joel mentioned I like to rock the Jake between hi and low postions and off to maintain the appropriate speed. There is no right and wrong to this just a preference. You need to always manage your speed while keeping the engine at 2100RPM or less by adding the service brakes to the jake braking as needed.

If your coach is programmed to go to 4th gear when you select the jake brake you then also need to know the max speed that you can turn it on at and still stay within the engine 2100rpm limit. That speed is likely to be under 65mph. If that is the case you may want to go to an Allison shop at some point and have them change that to a 5th gear selection. The gear that the Jake goes to will be found in the upper right corner of the Silverleaf screen while it is set in the drive position with the jake enabled at highway speed (50-60mph).

Later Ed

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