10-20-2016, 02:42 AM
Newmar Owners Club
Join Date: Jun 2013
Location: Apple Valley CA
Originally Posted by Dutch Star Don
"RIDER FAN"......I can give you some advice on driving your coach, because I had the same coach for ten years (2005 Diplomat).
To start, and not to offend anyone, the old saying of going down a hill at the same speed you went up, is an old adage that doesn't apply to many modern coaches. My 05 Diplomat had the power to climb 6% - 7% grades at 60+ mph, even while towing, yet the Exhaust Brake was incapable of holding the coach back at those speeds on a 6% - 7% downhill.
Your Allison will NOT allow the engine to over rev and will NOT downshift if the rpm's are too high. Your exhaust brake has just enough power to MAINTAIN downhill speed when turned on at 55 mph or less on grades that are 5% or less.
Anything over that speed and your exhaust brake will do little for you. Anything over 5% and your coach will gain speed proportionally to the steepness of the grade.
Your first downshift when the exhaust brake comes on, is typically 6th to 5th. Again, only a little help on slight grades. Your next down shift will help, but still won't hold the coach back. On my Diplomat, I eventually had to get to 44-45 mph, a downshift to third, before the coach would hold on grades above 5%. So.....if you know it's a steep/long grade, you'll want to get down to the 44 mph speed. I short grade, you'll be back on flat land before the coach builds too much speed.
Here's the problem.....descending grades at 45 mph usually brings an onslaught of semi's and other RVers roaring down your back side. Many will say, who cares, but it can be disconcerting and I hated it. It typically took a lot of work, both selecting speed, stabbing brakes and paying attention to the overall grade when using the exhaust brake.
This may not be the answer you're looking for, but it's what I found worked best for your coach after ten years of driving my Diplomat all over the mountain ranges out west. The only one where all the rules go out the window is the Eisenhower grade in Colorado.
When I owned the Diplomat, I was towing a Chevrolet Silverado 4 door. I knew when I eventually changed coaches, my next coach would have an engine brake. The newer coaches allow the engine brake to work with the cruise control and automatically adjust speed on steep grades. It's now a lot less work and I can descend most grades at whatever the rest of the traffic is doing.
Couldn't have said it better myself Don.
Craig & Carolyn Roberts Apple Valley, CA
Toad: 2017 GMC Canyon 4X4 Crewcab