Prime Inc Is Disabling Manual Mode On Their Trucks With The D12 Manual Automatic Transmission !

Noob question: if the manual mode is disabled and you're descending steeper grades in snow or rain w/o jakes, won't it keep trying to shift to higher gears on you as the truck accelerates?

I'd read about making sure to be in the correct gear for the grade from ahead of time to avoid accelerating too fast and burning up the service brakes.

Yes. It will IF you are going too fast as you start down that hill. This is where driving the appropriate speed for conditions is vital. It is all about momentum.

If you begin descending the hill at 50mph (depending on how steep it is), you are going to need to use your service break frequently in order to keep the truck from going too fast. This is dangerous as it could cause the breaks to fade (overheat).

If you begin your descent at 30mph, the truck has less momentum and you will not be required to hit the breaks as often in order to maintain a safe speed. It takes practice and experience to learn the correct speed to descend hills at various weights and speeds, and in various conditions.

Alright everyone, just to be clear, I have no problem with the automatic per se. As I said in the post, I’ve gotten used to it after a few years of driving one. My problem is with disabling the manual mode. Just yesterday I was on a 6% grade about 5 miles downhill and I was around 60,000 lbs. So following the instructions for descent control given by Freightliner, I slowed down well in advance of the hill to about 35 mph ( truck speed limit was 45 mph) with my flashers on. I put the truck in 9th gear and engaged the engine brake to the middle position and I set the cruise to 35 mph. It did alright. I didn’t have to touch the service brake the whole way down and it maintained a speed of about 35-40 mph and the rpms were good. I even passed another truck that was going slower than 35. But it still wanted to downshift to 8th gear a few times which would rev the rpms, and I would adjust the engine brake and then it wanted to up shift to 10th gear a couple times which would increase the speed. And in those instances, being in manual mode would have been better to hold the gear and by working the engine brake, keep a steady speed and rpms. The name of the transmission is a Manual Automatic Transmission. They built in the manual mode for a reason. And I still haven’t heard anyone here explain how they control descent in the winter, besides the obvious slowing down and lowering the gears, when you shouldn’t be using cruise control and even the engine brakes.

You guys do know that you can turn off E-Coast on Freightliners??? Settings menu buried in there. Have to manually turn it off every time you start the truck other wise it defaults on.

Ironically, Wilson has that disabled, but still allows the use of manual mode. Now if only they'd set the cruise control over/under speed to less than 5 over set speed before it starts slowing you down.

Running at 65 it'll give you an overspeed before slowing you down if you try to let it work as intended.

You can also change the setting for the cruise control in the same menu options as turning off or on Creap Mode and E-coast. You can adjust the over and under speed as well as the follow distance in seconds.

Alright everyone, just to be clear, I have no problem with the automatic per se. As I said in the post, I’ve gotten used to it after a few years of driving one. My problem is with disabling the manual mode. Just yesterday I was on a 6% grade about 5 miles downhill and I was around 60,000 lbs. So following the instructions for descent control given by Freightliner, I slowed down well in advance of the hill to about 35 mph ( truck speed limit was 45 mph) with my flashers on. I put the truck in 9th gear and engaged the engine brake to the middle position and I set the cruise to 35 mph. It did alright. I didn’t have to touch the service brake the whole way down and it maintained a speed of about 35-40 mph and the rpms were good. I even passed another truck that was going slower than 35. But it still wanted to downshift to 8th gear a few times which would rev the rpms, and I would adjust the engine brake and then it wanted to up shift to 10th gear a couple times which would increase the speed. And in those instances, being in manual mode would have been better to hold the gear and by working the engine brake, keep a steady speed and rpms. The name of the transmission is a Manual Automatic Transmission. They built in the manual mode for a reason. And I still haven’t heard anyone here explain how they control descent in the winter, besides the obvious slowing down and lowering the gears, when you shouldn’t be using cruise control and even the engine brakes.

The one time I've had to run without jakes down a grade was coming out of Medicine Bow towards Laramie, WY. Corners were slicked over and most of the road was wet. I did between 10 and 15mph down with ~25k in the box. When I hit the bottom I could barely smell my brakes (I basically had to stick my nose right next to them -- wanted to check on them when I hit the bottom.)

So, ballparking, I'd say take whatever you run x grade at with the jakes & weight and cut that speed in half to descend using only the service brakes. It miiiight be a little excessive but not being able to use jakes makes me incredibly nervous about my ability to respond to, say, a stalled vehicle in the travel lanes hidden behind a curve. I empathize with the frustration over them disabling that setting --- whether or not a truck can be driven safely without some functionality or other, under ideal circumstances that decision should be left in the driver's hands.

As a tanker I live by manual mode when taking off, especially when starting going up a hill. The economy mode that is default wants to skip shift because the way the liquid surges. This causes issues if it skip shifts from say 2-4 when taking off the truck will wont have enough power to move and you will come to a dead stop as the transmission finds the right gear now that the liquid has surged back onto the drives. Even Peterbilt has said “the way Prime has the ecm programmed for tankers is killing these trucks.” I’m l/o so I will still have my manual mode, but company tankers deal with chaos multiple times a day.

But what's interesting is, I run much heaver tanks than anything Prime has, every day with an auto Pete, and have never had these issues. It's drivers not willing to learn how to finesse an auto these days that's the problem.

And that's my unpopular opinion of the day.😊

Roehl also disabled manual mode. Another thing I noticed, they disabled self-cancelling turn signals on all their trucks.

Yes. It will IF you are going too fast as you start down that hill. This is where driving the appropriate speed for conditions is vital. It is all about momentum.

If you begin descending the hill at 50mph (depending on how steep it is), you are going to need to use your service break frequently in order to keep the truck from going too fast. This is dangerous as it could cause the breaks to fade (overheat).

If you begin your descent at 30mph, the truck has less momentum and you will not be required to hit the breaks as often in order to maintain a safe speed. It takes practice and experience to learn the correct speed to descend hills at various weights and speeds, and in various conditions.

Thanks. I misunderstood that keeping it in a certain gear would prevent the truck from accelerating past a certain mph range for that gear.