TEMPS: Downhill in a PT-42 Series 60/Allison

[Pete Masterson]

In slightly rolling hill country, I use the cruise control and set the jake to "low" ... it will keep the coach in a reasonable speed band. On more gentle slopes, the jake will slow down the coach by about 5 mph before the cruise control kicks in to accelerate. Probably uses more fuel in that situation. I generally turn off the cruise control in rolling hills as it's not very good at maintaining an even speed in that situation, since it doesn't anticipate the next up-slope, so I can do better by letting the coach gather a little extra speed at the bottom of a hill to let the momentum help with the next upgrade.

Kurt, what is this mode 1 and mode 2 you're talking about? I hadn't heard anything about it. (I'll have to go looking for my Allison manual -- I'm pretty sure I have one in the blue box somewhere.)

On my coach, when I'm under jake brake operation the up-shift doesn't occur until 2400 RPM. The engine book explains that "under power" the maximum RPM is 2100 but under no power, the engine is allowed to go to 2400 RPM. (I try to avoid letting it run up above 2100, as much as possible anyway.)

I note that when it's at or above 2100 RPM and I step on the throttle, then there's a big delay while the transmission up-shifts before the power comes back on. 

As you say, 1800 to 2000 RPM is a pretty good sweet spot for the jake brake.

Pete Masterson

'95 Blue Bird Wanderlodge WBDA 42

El Sobrante CA

"aeonix1@mac.com"

On Jun 17, 2008, at 2:35 PM, bumpersbird wrote:

<snip> By the way if you run with the cruise on turn off the 

jake brake. It will activate and fight the cruise control. At least 

it does on my coach.