I took a very nice ride today in a 2002 Monaco Knight we intend to purchase. The unit has an exhaust brake. I asked the dealer how the exhaust brake functions, and what the difference was between an exhaust brake and a jake brake. I didn't get a very good answer to either question. Hence I'm asking the forum members.
When I activated the exhaust brake, the coach decelerated nicely. However, the engine RPM also increased incrementally, almost like the transmission was down shifting.
Can someone please explain what is going on here in basic technical terms?
Is the "exhaust brake" simply slowing the coach by down shifting, or is there really some kind of compression braking going on?
What is the difference between a Monaco "exhaust brake" and a Jake Brake? Are there Pro's and Con's to either type?
The exhaust brake is a butterfly valve located in a cast housing that the engine exhaust passes through. When engaged the valve closes which causes resistance to the flow through the valve. At the same time the system automatically selects a lower gear to increase the flow causing increased resistance. This resistance transfers to the drive wheels which slows the vehicle. The downshift selected is programmed to 2nd or higher. To know which gear yours is programmed to, observe the display on the Allison shift keypad when the EB is engaged. In larger engines Jake brakes are used. The Jake brake changes the engines valve operation causing the same back pressure affect and slows the vehicle Both are very affective and, if used properly, can extend the service brake shoe wear to 2 or more thousand miles.
The Jake brake is much more powerful than the exhaust brake because the jake vents the cylinder air pressure at the top of the compression stroke so that it doesn't push down on the piston for the power stroke. The exhaust brake chokes off exhaust flow but leaves this higher pressure in the cylinder during the power stroke therefore, not as much overall resistance is created.
This usually rattles some cages, BUT any brake made by Jacobs is referred to as a Jake rather like their generic name. Been that way for a hole bunch of years... Does make it rather confusing for some... You may very well have a Jacobs extarder which restricts exhaust gasses as has been mentioned and not a Pac Brake... All engines are air pumps wether they alter the valve timeing or not. And yes, most exhaust brakes work in conjunction with the transmission's down shifting. Makes it a very effective brake... My previous engine brakes, I activated only as needed. My exhaust brakes I never turn off...
Operation of a jake is not that much louder than the engine running.
Its the truckers with the open pipes you hear 5 miles away.
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I agree that the compression brake is much more efficient. Also, most of the noise is muffled in a motorhome because of the muffler that most large trucks have eliminated. The compression brake ususally has two settings, 3 or 6 cylinders or low and high. In the low position only three of the cylinders are effectively changed into a compressor. In the high setting, all six are in the compressor mode.
In the PacBrake, the most common type of exhaust brake, the down shift is programmed. Most are programmed to go to 3rd with reprogramming to 2nd or 4th possible. I have left mine at 3rd gear as it seems sufficient.
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