Service Brakes w/ Retader, Panic Stopping

[Itchintogo]

I think it depends on where your driving. Out here in the Rockies and Cascade mountains I am confidant you will find a very large percentage of trucks and buses are running with their jakes on all the time. Due to mountainous terrain and tight reduced speed corners is really saves on the service brakes, helps you control momentum and saves you from flipping the switch constantly. There is usually a sweet spot you can feather the accelerator to more or less coast. Of course if your following a vehicle and waiting to pass I probably would shut it off to keep the jake from cycling. Brake lights don't come on in a highway truck when the engine brake engages.

Out on the prairie I would drive with the Jake off and I think most people do. Switching it on when required. When slippery you must be cautious and this is when sometimes with a long grade and a heavy load I would engage the engine brake in stages usually 3, from low to high, gradually increasing the torque resistance on the drive wheels. Extreme icy conditions, I have come off the Coquihalla Hwy in first gear edging down the mountain with no engine brake on. When it gets that bad I generally have a rule that it is time for bed!

But more to the point. The example given was a panic stop situation. So if we are reducing speed at the greatest or maximum rate of decline then you may achieve a slight advantage by having an engine brake or retarder engaged but in my opinion it will be very minimal. There is no way a driver can safely control the vehicle and down shift to achieve maximum RPM braking power and/or the Allison transmission will be hunting and pecking and can't find the appropriate gears fast enough to achieve maximum braking power, when the wheels are either locked up or shuddering with ABS activity. The rate of speed and engine rpm loss are in a type of "free fall" during the event. It would be next to impossible to find the correct gears fast enough. For that reason, in my opinion the engine brake likely won't make an appreciable difference in stopping distance.