Getting to know the New Cascadia and Detroit DT12 Transmission

by | May 3, 2019 | Driver News | 0 comments

As Crete continues to transition to a mostly non-stick shift fleet, many drivers will be getting new trucks without the 10-speed stick shift that they have loved their whole careers. Times change and technology moves forward. We drivers have to be able to roll with the changes that come our way. But being human we are often hesitant to change from what’s been comfortable to something new. In the long run, it usually ends up being for the best. In the case of the new automated manual transmissions, the payoff is several fold.

With fuel being the single largest expense the company incurs in operation, utilizing new technology to reduce fuel costs is very important. Increased fuel efficiency increases profits for the company which provides the income to raise our pay. I don’t think anyone will argue against that. But there is a learning curve that comes with any new technology. So let me see if I can help make it easier for some of our drivers to get the most out of the DT12 transmission.

First, let’s go over what the transmission is, and is not. It is NOT an automatic transmission. It is a 12-speed automated manual. It doesn’t have a torque converter. It doesn’t use automatic transmission fluid. It does have a clutch and uses the same standard gear oil as the manual transmission you had before. The only real difference internally is that instead of a long lever manually selecting the gears, it is all done with air actuated servos that are computer controlled. At times you will notice an alert on the center of the dash saying “Low Air Pressure. Transmission may not shift.” Be patient and build up some air pressure before you go so the transmission can operate properly.

One important item to remember is that the transmission does, in fact, have a clutch. Why is this important? When we used a manual stick, we would come to a stop, hold in the clutch, and generally only use light pressure on the brake pedal to keep us from rolling. A simple thing we did countless times a day right? Well, in the DT12, coming to a stop and just applying light pressure to the brake can lead to increased wear and stress on the transmission.

Here’s why. Believe it or not, you do have a clutch pedal with the new transmission. It is incorporated into the brake pedal. When you are at a stop and hold the pedal firmly, this does two things. First, it engages the hill holder feature that prevents you from rolling backward for a moment when you release the brakes and gives you time to apply the throttle and start rolling forward. But second, and more importantly, a firm application of the brake pedal tells the transmission that you intend to remain stopped and the servo disengages the clutch. If you remain stopped with only light pressure on the brakes, then the clutch is being rubbed slightly and generating a lot of heat and excessive wear. You can get a warning message on the center dash display stating that the clutch is overheating. “Downtime at a shop because I smoked a clutch” isn’t on my current “to-do” list.

If you listen closely as you become familiar with the transmission’s operation, you will notice a sound it makes when releasing and engaging the clutch. To try and put a sound into words, it sounds like a quick but soft “grrr, grrr, grrr.” You should spend a little time listening to this particular sound and feature before taking off on your first trip. Learn how much brake pressure you need to apply to disengage the clutch. And I’ll grant you, old habits die hard. I’ve been driving mine for over 300,000 miles and I still have to constantly remind myself to hold the brake pedal firmly.

The transmission has three modes: economy, performance, and manual. These are selected by the button on the tip of the transmission selector. Depending on the truck you receive, you may have only economy mode available or both economy and performance modes. I have heard of some trucks having the manual mode still available, but they will lock it out if they notice it during a service. If you receive a truck with only the economy mode, don’t sweat it. The difference between performance mode and economy is virtually unnoticeable. I was told it only adds an additional 100 rpm to the upper limit before an upshift.

This new engine and transmission package has different power and torque abilities that you may not be familiar with. They use what is called “downspeed” technology which allows the engine to produce its maximum torque at a really low 975 rpm. So don’t feel like you need to manually upshift early like we were once used to. Let the transmission do the work. They also have a higher operating redline limit than Detroit engines of the past. I’ll speak more on that later. You can manually upshift or downshift using the right-hand transmission control stalk by tapping it forward for a downshift, or pulling it towards you for an upshift.

One minor thing you don’t have to worry about is accidentally putting the transmission in reverse. Like modern cars, the drive and reverse are all computer controlled and cannot be engaged in the wrong direction by accident.

On the transmission selector lever, you also have controls for the three stage Jake Brakes. They operate very simply. Pull down one-to-three times to select the desired level of braking. You will also notice that you can now engage the Jake Brakes with the truck in cruise control without deactivating the cruise. Be aware that when traveling at highway speed your truck will downshift two gears and engage the Jakes rather harshly. So be extra careful that you have good road traction conditions when using this feature.

How does the DT12 do in the mountains on up and downgrades? In my opinion, it does a very good job. Climbing an upgrade is pretty straightforward. Just let the transmission do the work. Negotiating a downgrade is a bit more driver interactive. As you become more familiar with the limitations of the engine and transmission, you’ll start to know well ahead of time what gear you’ll want to descend a given grade at a desired—or limited by law—speed. With these engines being 15-liter models, the Jake Brake capacity is quite substantial. My first piece of advice is to start down the grade at a gear and speed lower than you think it can handle based on the grade, speed limit and weight of your load and see how it performs. You can always go up a gear more safely and easily than you can go down a gear.

As I stated earlier, these new Detroit engines have a high operational redline. In years past, they didn’t want you going much over about 1850 rpm. These new engines can run a full 2500 rpm, but, if you read your manual on the truck—and I can’t advise you strongly enough to do so—they don’t recommend letting it rev to over 2300 rpm. If you start to go over 2300 rpm for any length of time, a warning message to reduce rpm will display on the dash and you will have to either increase your Jake Brake setting, brake manually or if conditions allow, upshift.

With the higher limit available, the Jake Brakes can perform marvelously. When descending a grade I like to let the engine do the work with the help of the Jake Brakes. In fact, I grade myself personally on every hill I descend. With no outside influence like being cut off by another vehicle—if I reach the bottom of the grade without touching my brakes, then I was successful. If I have to brake beyond using gear selection and the Jake brakes I evaluate why that happened.

In my experience with the DT12 and the Jake Brakes, I prefer to descend most grades without the cruise control by selecting a gear that lets me hold the desired speed while flipping between stages two and three of the Jakes. Some people may want to keep it between a stage one and two situation which is fine as well. And then there are some grades where you can be in cruise control and just activate the Jakes and it will hold just fine. Experience will come quickly but always lean to the side of caution and safety first. My learning curve was rather short and harsh. I received my truck while under a load going from Lincoln to California and weighed in at about 79,800 pounds. Yeah, no pressure, LoL.

An alternative method is using the cruise control setting. You’ll notice at the bottom of the center display you have two numbers lit in green (-4) and (+5). These represent the limit the truck will coast under or above the selected speed before taking action. The (-4) is for coasting to save fuel on minor humps in the road like hill crests and overpasses mostly. But the (5+mph) one is where the Jake Brakes will automatically apply without driver input to keep from exceeding more than five mph over your set cruise limit.

Some drivers set the cruise control at five mph BELOW the speed they know they can safely descend a grade. Then the truck will automatically select the gear and Jake Brake level to maintain that (+5 mph) limit. Of course, this only applies to optimum weather and road conditions. I’ve used it and it does work quite well. As for me, I prefer to manually select my gear and feather the Jakes myself. Just a personal preference.

You will also notice that when you speed up and set your cruise control you can hold the (+) button and the speed setting will increase rapidly in five mph increments all the way to 65 mph. I like to use this feature when first starting out and entering an on-ramp by accelerating by the throttle up to 30 mph and then just holding down the (+) button for the cruise control until it’s maxed out so the truck gives it all that it’s got getting up to speed.

One thing you will quickly notice is that when approaching a situation like a stop light or stop sign the truck won’t drop below seventh gear until you stop. I have seen on a few occasions that just as I was about to stop, the light would turn green and then I would step off the brake and onto the throttle and the transmission would get confused and require me to stop for a few moments before it would select a gear and go. I found a simple solution to this minor glitch. As you slow down—once you are down to between 5-10 mph—tap the throttle very lightly and it will downshift to an appropriate gear before you come to a complete stop. This helps ensure you are ready to go in case the light does change.

I’ve heard some complaints from drivers about backing and unhooking from trailers. On unhooking, some drivers say they have a problem with the truck rolling back and re-hooking the kingpin. Remember earlier when I shared the part about holding the brake pedal down firmly? This same technique will eliminate that problem. The hill holder feature will hold the truck in place for a moment while you switch from brake to throttle to pull out. As far as backing, I find that giving the truck a second after releasing the brake and then just applying a touch of the throttle is all it takes to make the truck move smoothly in reverse. Take your time and be patient and realize that these transmissions do operate a little differently than the manual sticks.

My overall experience with these transmissions has been that it is a well-designed package that works seamlessly with the engine, cruise control, and Jake Brakes. And for those of us with less than youthful knees, it is a godsend in heavy traffic or tight maneuvering situations. Do I still miss my stick shift? Sure I do. I used to have a lot of fun with it. But for all the advantages and ease of use I have with the automated manual, I’m quite happy running one of these all day long. As a final note—there are multiple “How-To” videos on this transmission available on YouTube including one demonstrating a descent down Cabbage Pass.

As I can never recall all the various tips and tricks for an article like this when I am writing it, but always can when I am driving, be sure to chime in and add any additional items in the comment section.