engine-exhaust brake how does it really work?
Postmaster
Joined: Jan 2005
Posts: 4,424
Likes: 12
From: BC Canada
If it is holding a load down a hill, it is not going to release until you command enough throttle to overcome the load. It is load sensing so the heavier the truck and trailer, load, steeper hill, will require full throttle to release. This is a safety feature. Once it releases the hold back, it cannot take the load back, depending on the gear, it would have to over rev. This prevents a runaway in the event service brakes fail.
This engine can rev to 3500 rpm pulling, and 4200 holding back. Don't worry about the revs, that is what makes the exhaust brake the most effective. The higher the boost showing on the gauge, the more load it senses, the higher it will allow revving. The more the hold back capacity. Rev's are protected by the ECM and TCM.
By the way, it is an engine brake, not an exhaust brake, it is using the turbo, engine revs(why more effective at higher revs) the transmission gears and torque converter to hold back. Not a Jake which closes cylinder valves against the airflow from each piston, or a PAC which closes the exhaust pipe after the turbo.
This engine can rev to 3500 rpm pulling, and 4200 holding back. Don't worry about the revs, that is what makes the exhaust brake the most effective. The higher the boost showing on the gauge, the more load it senses, the higher it will allow revving. The more the hold back capacity. Rev's are protected by the ECM and TCM.
By the way, it is an engine brake, not an exhaust brake, it is using the turbo, engine revs(why more effective at higher revs) the transmission gears and torque converter to hold back. Not a Jake which closes cylinder valves against the airflow from each piston, or a PAC which closes the exhaust pipe after the turbo.
Mountain Pass
Joined: Jun 2020
Posts: 113
Likes: 6
From: Murfreesboro, TN
Well said, mhoefer! Where's the thumbs up button?
I haven't used the auto- engine brake. I've always used it in manual mode (the first mode I get when I hit the dash button). The way I understand it is; that the auto mode works like a down-hill cruise control. You set what your max speed should be on a descent and it will try to keep the truck from going above that threshold. Whereas the manual mode engages maximum engine braking. There are instances when manual mode could offer TOO MUCH braking action. That's where the auto feature comes in handy.
I haven't used the auto- engine brake. I've always used it in manual mode (the first mode I get when I hit the dash button). The way I understand it is; that the auto mode works like a down-hill cruise control. You set what your max speed should be on a descent and it will try to keep the truck from going above that threshold. Whereas the manual mode engages maximum engine braking. There are instances when manual mode could offer TOO MUCH braking action. That's where the auto feature comes in handy.
Mountain Pass
Joined: Mar 2020
Posts: 149
Likes: 9
From: San Juan Capistrano CA
Found an interesting use for the exhaust brake. When you have cruise control activated and are going down a steep hill, the transmission will shift into a lower gear to keep the speed constant. With the exhaust brake engaged in "auto", going down the same hill at the same speed, the computer uses the exhaust brake to limit downhill speed and the truck never downshifts. I have tried this experiment several times and the outcome is consistent.
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