Engine brake
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Elder User
Joined: Jan 2008
Posts: 837
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From: Newark, Delaware
Engine brake
Ok, I need some schooling from the diesel gods. The other day at work I was helping one of my sergeants work on one of your MTV's. That is the Marine Corps' "Medium Tactical Vehicle" aka 7-Ton. It has a Cat C-12 engine and an Allison tranny. Anyways, I was in the cab doing some tests and such and I saw the switch for the engine brake. I always thought it had an exhaust brake because thats what it sounds like when engaged. Now on to my question. What is an engine brake, and what are its pros and cons compared to an exhaust brake?
Post Fiend
Joined: Dec 2008
Posts: 7,649
Likes: 2
From: Wallingford, CT
Let's say your engine has 2 exhaust valves. If you have an engine brake on it will keep one exhaust valve closed or partly closed which doesn't allow the exhaust gases to escape as quickly slowing down the motor thereby slowing down the truck.
I believe that is how it is. Had to quickly consult dad on that one. I'm sure someone who knows more about these systems than me will chime in soon.
I believe that is how it is. Had to quickly consult dad on that one. I'm sure someone who knows more about these systems than me will chime in soon.
Senior User
Joined: Oct 2008
Posts: 136
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From: Littleton, CO
If I have the story straight, an engine brake (aka "Jake Brake") will alter the valve timing so that both intake and exhaust valves are closed during either the up- or down-stroke to create pressure (up-stroke) or vacuum (down-stroke), then opening the exhaust valve briefly at ~ TDC/BDC to relieve the pressure/vacuum and start all over again in the opposite direction.
I think the exhaust brake just builds up exhaust backpressure to kinda-sorta do the same thing, but on a much smaller scale - and without the big modifications required to the valvetrain.
That's my understanding, but I'm a diesel noob so apply sodium liberally.
I think the exhaust brake just builds up exhaust backpressure to kinda-sorta do the same thing, but on a much smaller scale - and without the big modifications required to the valvetrain.
That's my understanding, but I'm a diesel noob so apply sodium liberally.
