Looking for some education on engine breaking. Please be patient. I'm old and a slow learner. I think I understand a bit about how the fins in the turbo shift to create back pressure to slow down the motor resulting in slowing down the truck... Makes the engine work harder so your tranny and brakes don't have to.. right? What is the difference between how these two choices work? I live on top of a hill. I've played with both and had good and bad experiences but would like to understand what I'm doing instead of experimenting which sometimes causes much higher revs than I like. First trying to understand the Manual mode. Do I have to be on a descent before engaging? I click the button once and I go into Manual engine breaking. How does the truck know what speed I'm looking to maintain? Do I apply the brake to the speed I want and then the truck will maintain that speed? Do I wait until I'm at the speed I want and then click the button? I know I have more questions but want to understand this in pieces. Thanks

 

The basic understanding is Normal works to slow the truck down, Auto works to maintain a set speed.

Both work better in Tow/Haul but it isn't a requirement.

It's better to have either selected before descent. Auto works fantastic with Cruise Control set, Normal works better as you manually downshift the truck. If you approach a hill in Auto at say 60mph, without CC set, and want to maintain 60mph, tap the brakes and the computer will maintain 60mph down the hill. In Normal mode and Tow/Haul, when you crest the hill it will slow the truck down well under 60mph. This is where you'll find yourself having to accelerate to maintain speed.

I like Auto and Tow/Haul with Cruise Control set with my Toy Hauler on I-70. The computer does all the work, it's awesome with no need to brake.

 

Thanks. Right now I'm not towing but need to travel down a long hill every morning. What would be the best way to work the truck for my situation? I want to go down my hill around 35mph but reach the hill doing about 45mph.. Use Manual mode and manual shifting the truck into 3rd gear seems to work..just wondering if there is a better way. I tried doing the same with Automatic mode and leaving it in drive.. sometimes works fine and sometimes rpm's jump past 2500 which feels strange.

 

Set cruise to 35mph with Exhaust Brake set to Auto at the top of the hill.

 

Truck wasn't happy with that. Bucking and jerking and high revs.. I hit the brakes, shut off the engine brake, drop it into manual, upshifted several gears and accelerate a bit to calm things down. Maybe I'm going too slow for the truck to handle the Automatic Engine brake? Even without cruise control she doesn't seem to like it. Tomorrow I'll try putting the truck into manual with 3rd gear along with manual engine brake and tap the brake as I crest the hill. I'll see what she does with that combination.

 

The engine brake only has hold back at higher revs. It’s not Hurting anything to rev, as the red line holding back is higher than on the throttle. I use normal engine brake, drop gears down as I go over the top to hold at desired speed, subtract one more gear if it seems to be pushing faster, the only limit is it won’t shift down if it will result in an over rev. Then the foot brake is required just enough to allow the rpm room to shift down. If it’s hold back is to much, apply a bit of accelerator. Don’t try this on a slippery road, it will get interesting. It is load sensing, so the heavier the truck load, the steeper the hill, or if your towing, it will increase hold back with revs. Higher the revs it’s pushing, the better the hold back. If you put up your turbo gauge, you can see the boost building to max pulling boost doing hold back. Once you get used to it, know how much hood back, what speed, I have found I can bring the truck right to a near stop, dropping gears, with or without my trailer.

 

Manual mode will basically go to max braking (100% on closing the turbo vanes), and act just like the tow/haul mode does in that it will downshift each time you apply the service brakes whether or not you have the tow/haul mode engaged or not (assuming you're in drive). I have a very steep incline (15%) near me and have found that either in auto or manual going down that hill the engine will rev high and upshift two gears, losing all engine braking. It's the only hill I've ever had it do that on, but it will do it without exception. My go to mode for that hill now is manual engine braking and manual transmission selection, which is actually one of my favorite ways to use it.

Auto will hold you down to the speed you're at when you select auto. This can be nice when going down mountain passes and you want to slow a few mph on the corners but otherwise maintain a decent speed, as it will allow you to apply the service brakes without automatically downshifting to the next gear and continuing to slow down out of the curve. In auto it will modulate the amount of turbo vane closure required to hold back your speed, and will automatically downshift as needed to hold that speed. I use three modes, depending on what I'm trying to accomplish - Manual with trans in D, manual with transmission in manual, and auto with trans in auto.

 

For your situation cruise control and auto mode would likely work well. Keep in mind that tapping the brakes while on cruise will kick cruise off. If you have adaptive cruise control your truck’s wheel brakes will be automatically applied in conjunction with the exhaust brake.

Here is the difference between exhaust brake “on” vs “auto”:

When exhaust brake “on” is selected the vanes in the turbo adjust to create the maximum back pressure they can. If you touch the brakes the truck will know you’re wanting to slow down and will aggressively downshift to help you slow down. If you manually select a gear in the transmission the exhaust brake will do its best to slow the truck as much as it can in that gear. So say you are travelling down the highway towing a heavy trailer and you start descending a steep grade at 60 mph with your EB set to “on”: The truck will likely start to accelerate so you lightly apply the wheel brakes. The truck now knows to downshift and it will start dropping gears. Say you take your foot off the brake once the truck drops to 4th gear and 60 mph. The EB will build as much back pressure as it can trying to slow the truck down. If the truck is gaining speed you might brake again until the transmission drops to third gear. You let go of the brake and the EB will build all the back pressure it can in third gear trying to slow the truck down. If the truck slows too much you will have to feed it some fuel with the accelerator.

When auto is selected the exhaust brake tries to maintain the travel speed you were going when you last let off either the brake or accelerator. So say you have the auto set while you are travelling 60 mph and come over the crest of a long steep grade. You let off on the accelerator and the truck starts picking up speed. It already knows that you want to maintain 60 mph because that was the speed you were going when you let off the accelerator. There will be a lag time but as the truck accelerates down the hill it will start down shifting to try to hold you at 60 mph. Because the truck has accelerated some you might want to brake to get back to 60 mph or manually force some downshifts to get the engine rpm up but the computer already knows 60 mph is the desired travel speed. Keep in mind that if the truck accelerates to 65 mph and you apply the wheel brakes causing the transmission to more quickly down shift, the computer is going to learn a new set point the moment you release the brake pedal. If the truck gets down to say 3rd gear and it starts to slow below 60 mph the turbo vanes will automatically adjust to create just enough back pressure to hold 60 mph. If you decide 60 mph is too fast you can brake to 45 mph and the computer will learn the new set point. If you decide 60 mph is to slow you can accelerate to 65 mph and when you let off the accelerator the computer learns the new set point.
If the transmission needs to drop to 2nd gear and rev the engine to 4000 rpm to hold a heavy truck and trailer on a long steep grade ... so be it. 4000 rpm is the red line and the engine will not be harmed running that fast.