Engine Brake Question
Logistics Pro
Joined: May 2011
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From: Maine
I'm not saying it won't go into 10th, what I'm saying is at the same speed, it typically ran at a lower gear with the engine brake on.
FTE Leadership Emeritus
Joined: Sep 2000
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From: Stephensville WI
A Jake brake is a compression brake. A third valve ( usually not the exhaust valve) is opened at or near the top of the compression stroke, which releases the compressed air, then is closed. As the piston goes back down this creates a low pressure area or vacuum in the combustion chamber, which creates a braking force.
An exhaust brake blocks the exhaust flow, forcing the piston to compress air against an obstruction, which creates braking force.
A gas engine creates braking force by having the piston draw in air past a closed throttle blade, creating vacuum and braking force.
An exhaust brake blocks the exhaust flow, forcing the piston to compress air against an obstruction, which creates braking force.
A gas engine creates braking force by having the piston draw in air past a closed throttle blade, creating vacuum and braking force.
Fleet Mechanic
Joined: Dec 2021
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A Jake brake is a compression brake. A third valve ( usually not the exhaust valve) is opened at or near the top of the compression stroke, which releases the compressed air, then is closed. As the piston goes back down this creates a low pressure area or vacuum in the combustion chamber, which creates a braking force.
An exhaust brake blocks the exhaust flow, forcing the piston to compress air against an obstruction, which creates braking force.
A gas engine creates braking force by having the piston draw in air past a closed throttle blade, creating vacuum and braking force.
An exhaust brake blocks the exhaust flow, forcing the piston to compress air against an obstruction, which creates braking force.
A gas engine creates braking force by having the piston draw in air past a closed throttle blade, creating vacuum and braking force.
I have never seen an extra valve dedicated to an engine brake system though? I am curious what manufacturer uses this method vs the oil activated solenoid for the exhaust valve?
Lead Driver
Joined: Nov 2005
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Lots of great responses. The most curious is the "exhaust Brake" vs. "engine Brake". This is my first diesel engine and to be embarrassingly honest to admit, the damn thing scares the heck out of me when I pop open the hood. If the CEL light ever came on, bout all I could do would be to open up the hood to verify, "yep, I checked- the engine is still there", then close the hood. My weak understanding and a greatly ignorant over simplification of the braking types, engine vs. exhaust, is that with an engine brake the compression stroke is used to slow down, that's why I down shifted, grant you that was a 460cid backed by a 4 speed manual shift trans. But if the turbo needs RPM to work, I am not really understanding how, when the fuel component is removed from the process how does it cause excessive back pressure to slow. I kinda understand the exhaust brake valve concept. Isn't that what the old "Jake" brakes were, a butterfly kinda valve in the exhaust stream that when closed create back pressure.
The exhaust brake on the PowerStroke, as well as the RAM Cummins, maybe the gm too but I don't know for sure, uses the variable geometry turbo vanes to close off the exhaust flow out of the engine to raise back pressure in the cylinders to achieve braking affect.
An engine brake, aka "Jake Brake" is a compression brake, and there are actuators on top of the valves in the cylinder head to manipulate the valves which basically turns the engine into a big air compressor. When applied the fuel is shut off to the injectors, and the valves open to allow air into the cylinder, then closed before the compression stroke, then the exhaust is opened to release the pressure, that is the loud growling popping noise you hear from the 18 wheelers as they slow down. This is why they are known as an engine brake, and the one on our type trucks are known as an exhaust brake.
There is also an exhaust brake that has a flapper valve place in the exhaust system at the back of the turbo outlet that closes off by way of a actuator solenoid to create the exhaust back pressure, works the same way as the one on our trucks, just that ours uses the vanes in the turbo instead of an outside valve.
Cargo Master
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From: Ridgway, CO
FTE Leadership Emeritus
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From: Stephensville WI
I always thought they were operated by an electric solenoid, but I'm probably incorrect.
More Turbo
Joined: Feb 2011
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Now tow/haul mode changes shift points but I haven’t seen a difference with the exhaust brake.
Looking forward to pulling to 6,000-9,000 feet above sea level next month. Should be beautiful up there. I typically stay in the “under 1,000” feet below sea level. The exhaust brake works great in Appalachians and I’m sure it will do great in the Rockies.
Cargo Master
Joined: Jul 2021
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From: Ridgway, CO
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Brett Foote
FTE Leadership Emeritus
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From: Stephensville WI
Me too, on modern engines anyway. Not finding much.
Fleet Mechanic
Joined: Dec 2021
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I just have never seen a cylinder head with a dedicated valve for only the engine braking feature. Every system ive seen has used the exhaust valve for engine braking function usually through a solenoid piggybacked to the valvetrain.
FTE Leadership Emeritus
Joined: Sep 2000
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From: Stephensville WI
OK, I did find on newer Jacob Brake systems the exhaust valve ( or valves if multiple) is used, not a separate valve. This allows the turbocharger and muffler to mitigate the compression brake noise associated with past systems.
Mountain Pass
Joined: Jun 2011
Posts: 202
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From: Extreme Northwest, Pa.
Lie - O - meter
My two cents, if your watching the MPG on your display then it may be correct, but then again . . . If your off the throttle, going downhill with the exhaust brake on and your mileage decreases, the engine works a little verses exhaust brake off coasting down the same hill. Try with and without the exhaust brake on and pay attention to your RPM's as well. Throttle off, and even if your RPM's rise a little common sense says your not putting any more fuel into it than at an idle. Can't wrap my head around mileage going down. lol As far as it wanting to use a lower gear with ex. brake on, it might be something in the programming. Seems there was a recall on a re-flash for the transmission not long ago, don't know if this would fix or have anything to do with your issue.
Seek out a very good Ford diesel tech and pick his brain.
Seek out a very good Ford diesel tech and pick his brain.
Cargo Master
Joined: Jul 2021
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From: Ridgway, CO
This was the pic I was looking for. Not current tech, off a old Big Cam IV Cummins. Looks to me like the solenoid on this version is air operated. If you zoom in a little the nipple on the outside looks like an air fitting and not electrical.
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