F-350 transmission questions

[MOAK]

It’s amazing; I’ve spent the last couple of months, on and off, trying to find an answer to a simple question. I have the 10R100 transmission. When in 4L I can only manually shift it to either 1st or 2nd gear. It will automatically shift up to 7th gear, however it will upshift only by getting the rpm’s up to around 2500, which is ridiculous because there is 400ft lbs of torque at 1600 rpm’s. My questions are- why can’t I manually shift any higher than 2nd gear? Is it supposed to work this way? If so, I’ll learn to live with it, but it seems counter productive to have to come to a full stop on the trail before and after crawling through or over an obstacle. Any ideas?

 

[MidOH]

Yes. Switch back to 4hi.

4 low is only useful in 1st and 2nd gears. For crawling. If you're tempted to go to 3rd, switch back to 4hi and 1st or second gear.

The truck is trying, desperately, to keep you from destroying it. All that power, through the 4 low gear reduction, is bad mojo.

 

[MidOH]

I switch to neutral, while rolling, to get in and out of 4L. 3mph maybe.

After crawling over an obstacle, I crawl along for a lil while.

Same for my Ram. But the Ram has no manual mode. You have to use the lockout.

 

[MOAK]

Yes. Switch back to 4hi.

4 low is only useful in 1st and 2nd gears. For crawling. If you're tempted to go to 3rd, switch back to 4hi and 1st or second gear.

The truck is trying, desperately, to keep you from destroying it. All that power, through the 4 low gear reduction, is bad mojo.

I’m not following, as I am somewhat dim witted when it comes to modern vehicles. The truck will not allow me to idle in 4th or 5th because it thinks I’m dumb enough to let the engine bog down instead of knowing enough to downshift? But it will allow me to manually be in an unhealthy high gear in 4H. Am I thinking backwards? I don’t understand the problem with 400lbs of torque at 1600 RPMs in any gear. Wow- automatics for dummies 101- I’ll get used to it. With the old stuff we would travel all day long in 4L.

 

[MidOH]

Because that's, at least, 1088 pounds of torque coming out of xfer case. More likely around 1500 with the torque converter. Way more than enough to snap things.


Why do you need 3rd gear in 4 low?

I didn't have an opportunity to duplicate this today with my 17. The truck might just be confused.

If it really is locking out thr high gears, it's most likely to protect the chain in the xfer case. Nailing a pot hole at 30mph could send thousands of pounds of force into the driveline, and the drive line won't give since its in low. In high it would likely just smooth that hit, with the torque converter.

 

[highboy4x4]

 

[MOAK]

I’ve attempted to make sense of it. To no avail. It will automatically shift up to 7th gear when in 4L as long as you wrap up the rpm’s to over 2200 or so. As soon as you come off the throttle it downshifts and maintains those high rpm’s. The higher rpm’s would create a lot more torque than being able to manually shift up, off of idle, the same as one would shift a big truck with a 10-13 or 15 speed transmission. (If idle is 800 then only wrap up to 1200 to float the next higher gear ie shifting off idle) A lot of folks have asked, as you have, why would you want to tool around in any high gears in low range. My 76 40, my 89 F250, my Rubicon and my 80 series all had plenty of torque to idle down the trail with ease while in 3rd while in 4L. With this ten speed that would be right around 5th or 6th gear, with ease. Pulling an upgrade, or coming to an obstacle of some kind, drop down to the necessary gear and, idle over it. For me - running the trail is all about finesse. In nearly 50 years I’ve never broken any drivetrain parts. I stay away from the skinny pedal, there’s rarely a need to use it. I say rarely because of course there has been dicey situations that full throttle might be necessary, but very rare. The 6.8 developes 400ftlbs at 1500rpm. ( probably 200, if that at idle.) If it will not upshift until 2250 rpms which is right around 425ftlb of torque. So I ask you and Ford, is the drivetrain more likely to be stressed while shifting off idle? ( 200-350 ftlbs) or at 2250rpms? ( 400-425ftlbs) hopefully someone from FoMoCo can answer the question. In the meantime while trail running I’ll be shifting between 4H & 4L every time I come to any kind of obstacle that I can idle over in 1st or 2nd 4L then stop and shift up into 4H. I like this conversation. Keep it going.