Redline on downhills

[Rockin]

Driving this weekend with 20200# gross, on 6% grades at 50-65mph, when I would break, the tranny would downshift for engine grade breaking. Some times, it would shift to a low enough gear it would go well into redline, like 4000+ rpm.

Is it normal for grade breaking to let the engine redline? Should I be concerned about damaging the engine at these high RPM's?

I found I could prevent this by maintaining the speed where a downshift wouldn't redline and by using occasional light breaking to drop a couple MPH. Is there anything else to be done?

[Inspector]

It is my understanding that the TCM won't allow overspeed of the engine. It will cause an upshift if sees an overspeed.
Denny :D

[mdrag]

Rockin,

Inspector is correct. If you look at your tachometer closely, you will notice that the redline limit is marked in two different patterns - one is the limit for normal throttle input, and the higher limit is for the grade braking feature. The electronics will not allow the engine to overspeed during grade braking.

Check out the ALLISON GRADE BRAKING TECH TIPS (http://www.kennedydiesel.com/allison_grade_braking.html) on Kennedy's website for a detailed explanation of this feature.

[Rockin]

Thank you guys. I feel much better knowing grade brakeing in this RPM range is okay. I will continue to use the brakes to assist in controlling speed but won't throtle to protect the engine.

[More Power]

The powertrain programming is configured to limit engine rpm to no higher than 4800 rpm while in grade-braking. So, it is normal for the tach to show an engine speed up to as high as 4800 while descending steep grades with a heavy trailer.

Don't try that with a Dodge Cummins!

MP

[Colorado Kid]

Let me add that you can jump on the "throttle" all you want. . . above 3300 RPM the accelerator pedal doesn't effect anything.