Although Jacobs now makes an exhaust brake, a true Jake Brake works by forcing the exhaust valves closed rather than by closing off the exhaust pipe to create back pressure. I have had a coach with an exhaust brake and it would not activate with the cruise control on or anytime the throttle was partially open. The exhaust brake has the advantage of being silent but doesn't have nearly the braking force of an engine brake.
I do find that my Jake Brake and my cruise control do not play well together with my 4 speed non-electronic controlled Allison transmission. I get some bucking when the jake tries to kick in as the cruise control closes the throttle. I may leave the jake on when driving without the cruise control but don't leave it on with the cruise control.
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