Hi,

I'm new to the diesel and towing world, and I keep seeing comments about locking specific gears out. When I was playing with my manual override, I noticed that some of the gears would disappear from the list of gears on my dash (2021 6.7 10 speed)

Is that what I'm doing when that happens? Am I locking 10, 9, 8,etc out when they disappear?

Also, what purpose does this serve?

Sorry for my ignorance on the subject. I can't seem to find anything too useful to help me understand.

 

Transmission shifting heats up trans fluid pretty good. Going up and down hills/mountains can cause the transmission to shift... a lot. Locking out higher gears so the trans doesn't try to use them and maintains speed without shifting all over the place.

I also lock out higher gears when going down mountains to use the engine for braking. This is for gas engine... Not for sure about diesel as they have real actual engine braking.

 

In all reality, you very likely don't need to lock out a gear with this truck... I think some do it because of programmed mental hurdles of what they used to do, or what they think the truck should do, when in reality the truck will operate 100% as it needs to without any intervention from the driver. That is my personal opinion anyway.

 

If your in drive and your gears 1 2 3 4 5 6 7 8 9 10 are displayed near the tach gage and you press the - button on the shift column you will "lock out" one gear for every press of the - button starting with 10th. Pressing the + will allow the truck to once again shift into those gears that where locked out. Some of the reasons that this can be used is to reduce gear hunting while towing and/or in hilly country, more quickly heat up an engine, reduce lugging the engine at lower speeds, possibly preform a quicker dpf regen by raising rpm and exhaust gas Temps.

Manual mode is another separate mode:
The letter M at the bottom of the display can be selected by pulling the shift lever down one position. this turns your transmission into sort of a clutchless manual where the truck only shifts up-and-down through gears by pressing the + or - button on the gear selector On the shift column. In manual mode the truck will automatically drop gears To prevent stalling and lugging such as coming to a stop....the truck will down shift to prevent a stall but when accelerating backup to speed you have to push the + button on the gear selector to shift back through the gears the truck will not shift it on its own you have to (except when the truck senses lugging/stall). One of the main features of this mode as opposed to any other mode the truck has would be when driving down the road in 8th gear for example, if you would full throttle the truck in 8th gear at 55 miles per hour the truck will not drop a gear to accelerate faster, it'll stay in 8th gear until you shift up or down. This gives the driver more complete control control over what gear the truck is in and what are rpms you're driving at. * When locking out gears in drive if you accelerate hard enough the truck will still drop a gear, manual mode won't. This further reducing gear hunting when towing for example.

 

Interestingly, I find the new 10 speed to work very well. I have towed heavy for decades and have become familiar with 'over-riding' the bad decisions automatic transmissions often want to make when pulling hard.

I had fully expected the 10 speed would hunt with the gears being so close together, and that locking out gears would be the norm. In reality, hunting is almost nonexistent with the 10 speed/6.7. I put it in tow/haul, set the EB to manual, and rarely make a manual gear change.

 

Wow, great explanation! Thank you, good sir!

 

That might work in flat Georgia....but it doesn't work in the mountains.

What happens is, you'll start at the bottom of a hill in 6th gear at, lets say, 50mph. Once you hit the hill and start to lose speed, you press a little harder on the throttle and it downshifts to 5th. Now in 5th at 47mph, you get back up to 50mph...so you let off the throttle just a little to maintain speed, and the transmission upshifts back to 6th and you start to lose speed again...meaning you press on the throttle a little more and it downshifts back to 5th. 6th to 5th to 6th to 5th to 6th to 5th....all the way up the hill. I don't know about you....but I don't think that is how the truck NEEDS to function.

Locking out 6th gear at the bottom means no back-and-forth shifting from a computer that can't see the road and doesn't know what I want it to do. 5th gear smooth sailing all the way up the hill at 50mph (or whatever speed...I'm just throwing out a number)

 

"... set the EB to manual..." EB as in engine brake? So you're turning your engine braking on, and then selecting manual drive. Did I understand that correctly?

 

Yes, you are "locking out" those gears, but I believe it is actually referred to as "range select" when you do this.
This action makes it so the trans will not shift up to those locked out gears.
Doing this can help in towing/hauling heavy because it keeps the engine in a higher rpm range, making it more responsive and keeps the trans from shifting so much going up and down hills.
In my current truck with a 6 speed, when I tow heavy at speeds of 70 or less, I lock out 6th gear and it makes towing much easier and the fuel economy is better because it isn't lugging the engine so much.

Now, do you need to do this on this new 10 speed truck?
Depends on what you are using it for and the conditions and terrain and speed.
It is something you just have to experiment with as you use the truck.

 

Ah! So this explains why I kept seeing people say they locked out "6th" gear. They must have the 6 gear trannys. I was like, how the hell do you lock out 6th but not 7th-10th? lol

So, am I correct in assuming the heavier the load, the more gears you'd want to lock out?

 

Not necessarily.
As I stated, it is something for you to experiment with as you use your truck.
And, remember that when you lock out those higher gears, you can also lose fuel economy as the truck will run at higher rpm at highway speeds.
Many factors that affect how you would best use this feature.

And, yes, the trucks before 2020 were 6 speeds, older than that were 5 speeds, older than that were 4 speeds, older than that were 3 speeds, as far as automatics go anyway.

 

Great info. Thank you!

 

I'm setting the transmission to Tow Haul, and the EB to Manual (other settings for the EB are off or auto.

ATC gives a great explanation of why to lock out gears during hill climbing, but I have found with my current truck that gear shifting does not accompany small changes in throttle input when in Tow/Haul, so it does not have a tendency to hunt.

 

Ohhh.. okay. That's right, I remember seeing the options for engine braking when I pushed the button. Thank you.

 

So, Super... What are you towing, and what axle ratio does your truck have?