Quote:
Originally Posted by Always-Going
Also does anyone know what are the best speeds to down shift at and what are the RPM's / speeds to maintain when descending??
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There are two types of Engine Braking. One is called Compression Engine Brake and the other is called Exhaust Brake.
Not sure which one you are referring to so it's best not to confuse the two.
Here is a great article which describes how each one works.
Allison transmissions will not let you manually downshift until it has attained a safe speed to do so. You can manually select a lower gear BUT that doesn't mean the Allison will go there. The Allison's are smarter than their operators.
When the indicator pad states 2nd gear when using your Engine Brake, that is only an AIM point for the Allison. Once the coach slows to a lower speed the Allison will downshift automatically to the next lower gear until it reaches 2nd. If your speed increases it's up to you to reduce it with the service brakes.
It pays to know what your specific UP-SHIFT points are for your coach. When controlling descent speed with an Exhaust Brake it's best to keep the Allison in a lower gear such as 3rd or 4th. Once you hit 5th your coach will take off like there is no tomorrow.
When I am descending medium grades I keep the Allison in 4th gear until it reaches 52-53 mph. At 54 I know it will up-shift to 5th so I tromp on the brakes to reduce the speed 5-8 mph. For really steep grades I reduce my speed BEFORE the grade such that I am in 3rd gear doing 30-35 mph and have my emergency flashes on in the right lane.
Bottom-line, slower is better plus you will have more control of your rig and less shorts to clean up once you get to the bottom of the grade.
Dr4Film ----- Richard