"Locking out" gears...

memilanuk · July 22, 2023

This is another of those 'coming from Ford' things...

So... on my current rig (2018 F350 XL 6.2L 6spd) if I'm hauling something and don't want the truck to keep over shifting from 6th down to 4th on every little hill, I can use the +/- rocker switch on the shifter to 'lock out' 6th gear. The driver's display console will then only show 5th on down, with whatever gear the transmission is currently in (5th, 4th, 3rd, etc.) highlighted. This is separate from going to 'M'anual mode on the column shifter and then using the +/- rocker switch to manually *change* gears - although if I'm in 6th and lock that out, the tranny will bump down automagically.

From what I've heard/read, the GM/Chevy driver console only shows what gear/mode the column shifter is in i.e. PNRDL, unless you physically move it to 'L' which sounds like it's the analog to 'M'anual mode on the Ford. Is that about right?

How then, do you know what gear you're in when the transmission is running in automatic? Is there a function for 'locking out' say 10th or 9th gear, short of going to 'L' and having to run things manually? Conversely, the manual shows that if one goes from 'D' to 'L' the transmission will automagically downshift from 10th down to 7th (or lower, depending on where it starts from). Is it not possible to run in anything above 7th in manual or 'L' mode?

Edited July 22, 2023 by memilanuk

Another JR · July 22, 2023

You can pull up the owners manual and read about it, but I’ll summarize how the six speed works. I believe the ten speed functions similarly.

The “L” position is not a true manual mode (even though they call it that), but instead allows you to set the highest gear the transmission can shift into. The display shows “L5,” for example, if you are limiting it to fifth (locking out sixth). The display will show L5 regardless of what gear the transmission is in.

If you shift into L while driving in 6th or 5th, the transmission goes to L4. If you are in 2nd, 3rd, or 4th when you select L, it will drop one gear (if in 4th it will go to L3, for example). You can then use the rocker switch to move the maximum gear up or down, except it won’t let you over rev the engine by selecting too low an L setting.

memilanuk · July 22, 2023

So... the 'L' mode on the GM/Allison works like the normal 'lock out' on a Ford?

I'd been skimming the manual, but I was looking more for info on what gear was displayed, etc. I missed this:

Quote

This number is the highest gear that the transmission will allow while operating in L (Manual Mode). All gears below that number are available. As driving conditions change, the transmission can automatically shift to lower gears. For example, when L5 is selected, 1 (First) through 5 (Fifth) gears are automatically shifted by the transmission, but 6 (Sixth) cannot be used until the plus/ minus button on the shift lever is used to change to the range.

That there is *no* manual mode at all is a little off-putting. I've been using that quite a bit lately hauling a heavy truck camper, to keep the 6spd / integrated trailer brake control from down shifting too far when I tap the brakes coming down a steep mountain pass. Or to manually manage the gears going *up* a steep grade. Then again, with a different transmission, maybe I won't need it as much?

How do you know what gear the transmission is actually in *prior* to going to 'L'?

Edited July 22, 2023 by memilanuk

Another JR · July 22, 2023

28 minutes ago, memilanuk said:

How do you know what gear the transmission is actually in *prior* to going to 'L'?

There is no display that tells you what gear you are in. After two years driving the 6 speed I pretty much know what gear I’m in. I doubt I could develop such a sense with a 10 speed though. It shifts very smoothly though when you go to L and won’t let you overrev the engine.

memilanuk · July 22, 2023

@Dustin Marshall you've had both the Ford 7.3L w/ the 10 spd and the GM 6.6L w/ their 10 spd... do you miss not having 'M'anual shifter control?

the wanderer · July 22, 2023

1 hour ago, memilanuk said:

@Dustin Marshall you've had both the Ford 7.3L w/ the 10 spd and the GM 6.6L w/ their 10 spd... do you miss not having 'M'anual shifter control?

I don't see the point in a true manual mode. All you're missing (verses the lockout) is the ability to force an upshift and since these transmissions all already programmed to upshift whenever possible, I don't get why you'd want to lug an engine beyond what its tuned to upshift at.

memilanuk · July 22, 2023

We've been dealing with a 6 speed (Ford) that tends to over-shift (too far down) or gets to the point where it should upshift, but can't/won't, for whatever reason. Sits there stuck at the RPM for shifting up, and after a bit, things start sounding... not good. Options are either slow to a crawl in the middle of the road (interstate mountain pass) or manually kick it up a gear. Yes, it slows down a bit then, but it doesn't sound like there's a second engine starting up under the hood either.

UWSkier · July 23, 2023

I use the GM lock-out all the time. I just towed my camper cross-country with my 6.6L with Allison. I kept it at 8th gear for pretty much the whole trip, unless I saw some grades coming up. I'd manually downshift so the cruise didn't have to sense load and over-correct. Works great. I don't really care to know what gear I'm in. I can tell from the tach what gear it is.