Originally Posted by
Petervs
A quick review:
The bus is moving at some speed and you want to slow down. There are 3 common ways to do this:
A. The service brakes convert the kinetic energy to heat into the brake hardware by friction of the pads or shoes against the discs or drums.
B. A Jake brake uses the kinetic energy to compress air, which is then "wasted" out the exhaust system. No heat is generated.
C. A transmission retarder converts the kinetic energy to heat inside the transmission. The heat must then be removed by the transmission oil cooler. The cooler is a small "radiator" mounted in front of the big radiator and the transmission fluid needs to pass through here a time or two to cool off the transmission, which will take a few minutes or more depending on the outside temperatures and heat load on the transmission.
All three methods do slow down the bus. Method A and C will eventually reach the point where the heat added by slowing is greater than the heat dissipated by airflow. For a single stop in traffic all will work well. For lots of stops in traffic all will work well for a while, but eventually A and C will begin to reach their limits. For descending a long grade eventually A and C will overheat. B will just keep on working, leaving the service brakes fresh and cool.
For these reasons I prefer the Jake Brake. Especially if you live and travel mostly in the western states, almost anywhere you go you encounter mountain roads and passes. Knowing the Jake is ready to manage downhill speeds without needing the service brakes at all times is very comforting. You can select most any downhill speed by choosing the gear and setting the Jake on high or low. It is easy, effective, and the system has been trouble free.
Then there is the issue of some towns and their signs about compression brakes. I have noticed the wording of these signs varies from place to place. Some I have seen say "Unmuffled Compression Brakes Prohibited" , or " Jake Brakes Unlawful in city limits", "Use of Engine Brakes Prohibited" or some such.
I take the approach that in any kind of emergency, I will use all the braking systems I have no matter the signs in the area. Also, since the Prevost installation IS a muffled engine brake, it is not nearly so loud as what we typically heard on logging trucks, etc in the 1970's when the Jake Brakes came into common use and many of these signs sprang up. I have never heard of anyone getting stopped or ticketed for using the Jake Brake, but I would like to know if it has happened. Anyone?
Another interesting point, on my 94 the brake taillights come on when the jake brake is working, and when you step on the service brake pedal, the red light on the dash also comes on to indicate that. So, someone behind you might think you are riding the brakes all the way down a long hill when actually you might not have touched them at all. And if you are decelerating into a town that has several speed reductions as you come to the center, while the Jake is working any local policeman will see that you are slowing down and not ignoring his speed limit on purpose. SO far I have never been stopped for that either, and wear and tear on service brakes can be minimized.
One further note, I have driven both a Series 60 Detroit bus ( mine) and a 8V92 Detroit bus. The Jake effectiveness was noticably more in the Series 60 version when the setting on both was on High.
As always, comments welcome!
Peter vS
94 Marathon XLV