Hills/mountain descending?

I'm not EXACTLY sure I remember in the Cascadia. But down into 8th or 9th. Once I got the hang of it, 8th and 9th were all I needed to feel in full control and varying the engine brake to slow down or let it run up.

I was told the ISX is okay up to 2300 RPM and the Detroits up to 2000 RPM. Had no-o-o problem staying in range of 1500-1800 rpm, just that the gear you choose determines your downhill speed. Once that turbo kicks in you've got braking power to spare. (It feels great, too.)

Engine turns tranny, which turns rear end, which turns wheels. All geared to produce X speed at X RPM. As you gain experience, feel more comfortable, you can pick a higher gear and still feel captain of the ship, rather than prisoner in a downhill rocket. But with higher RPMs, each gear gives you more MPH.

I stay at least 5 MPH less than posted. Often 10 or more, on a hill I don't know. Don't expect to take a hill as fast as the guys who run it every day. They've figured out exactly where they need to stab the service brakes on each sharp curve.

 

Let's take Cabbage on 84 in Oregon. You should be able to stay in 9th gear and take it at 55 mph. Cabbage depends on your comfort level as any hill would. Homestake in Montana is 25 mph going eastbound. They take the though process out. If the grade is steep, and you're already in a lower gear, like 8th or 9th, you can usually stay in that gear to come down the hill.

 

fuzzeymateo & Richter already covered driving downgrades and (1-3) braking priorities flawlessly.

Another thing the OP questioned was winter driving, with snow and ice, so I'll address what wasn't yet mentioned.
Snow and ice are two completely different animals. Make no mistake & always remember that.
A few inches of hard packed snow, most times, will create a drag/resistance on your forward speed, whereas ice never will.

Not saying snow is "safe" either. Far from it. Snow does add a loss of friction factor in many circumstances,
especially when it is "wet" snow, and worse yet, wet snow in icing temperatures.

On flatland, ice is bad enough. On grades, it's extremely critical, and most times a dealbreaker (Pull over,, Shut down!).
In borderline icing temps, pay close attention to the especially to the backside of your mirrors, also other truck parts.
If you see ice forming on them, that's good enuf indication that any water on the roadway will also be ice.

Bottom line, know safety limitations very well, when dealing with any ice condition.
NO load is worth a "having to be there by xxx time" when icing reaches beyond any safe condition or level.

 

Another way to think about the role of your engine brake down a grade, downhill your wheels turn your rear end, your rear end turns your tranny, your tranny in turn turns your engine and it is the pressurization created at the pistons and piston cylinders that holds you back. Thin air and low rpms won't do it. Gotta get above 1500.

Winter driving--Learn the 'wiggle'!

In terms of winter driving and black ice, the key is slow down to where you're in control. If you wiggle your steering wheel when it's dry you'll get a 'feel' for how quickly your tractor should respond at different road speeds. Concerned about black ice?? Now, repeat that wiggle. Slow down to the speed that your tractor responds to that wiggle on ice and snow the way it did on dry pavement. Do it right now. Immediately. Slow down.

If you ain't got that wiggle, you're going too fast.

On ice and in snow, the weight of your load, especially a nice, heavy load, is your friend. Helps keep you in traction on the road. Once, coming upon a couple cars off to the side in extreme ice, I stopped to help. Pulled over past them and exited the cab, so slippery that I went right down on my knees, so slick I could not get up right. (And I grew up in Northern Minnesota playing hockey and the whole winter wonderland, the real deal.)

Anyway, I had to pull myself back up by the steps and had no place to go but back in the cab. Curious, I unlocked the differential and sure enough, couldn't move. Locked it back up, pulled away easily. I figured there was nothing further I could do if it was too slick to walk on and continued on my way. Hope they were okay.

If your load is light, that's a problem. One time in a blizzard, hauling mail (yeah, ya gotta keep going, just hafta stay safe) I had just left the Bloomington Annex and got up to the light on 46 on the overpass above 37. Across from me a city snow plow flashed his lights at me to keep coming as the light changed against me. I didn't want to run the red. He kept flashing. I kept slowing. He flashed all the more furiously.

Finally, I came to a stop. When the light turned green I couldn't go, wouldn't move. Wheels just spun there. I flipped the differential into lock and it just bounced, sat right there. A typical load of mail is really light. They have these carts (I forget what they call them) and each gets mail for a sorting and break out destination. So there I was, unable to move, just a short distance from my starting point. Light loads. Am I going back on a hook? No, no, no.

I remembered something a buddy had said. I slipped the tractor into higher gear and just let the wheels spin and as they turned, they slowly melted the ice under them. I could have walked faster but I got over the hill, through Bloomington (Indiana) and made Cincy just fine.

My run could have ended right there, unable to make forward progress for the ice and light load.

By the way, a good insulated monkey suit is also your winter friend. You can go Carhartt or Wal-Mart but mine keeps me toasty even working lying on the ground down into the low 20's. Have one with you as part of your winter gear.

Also make sure you carry 3-5 days worth of food and water from here on out. It's not too soon to get snowed in and there's already been a big snow and shutdown. Stay safe.

 

Isn't Cabbage westbound much steeper on the downgrade than going eastbound? I have only ever done it eastbound but have heard the westbound is the fast side.

 

Victor wrote: "I unlocked the differential and sure enough, couldn't move. Locked it back up, pulled away easily. I figured there was nothing further I could do if it was too slick to walk on and continued on my way."

Do you drive on slippery conditions with differentials locked? Is there a speed one should not drive above with them locked to avoid doing damage to the unit? Is it safe to unlock them while rolling? I understand they should never be engaged with torque applied, hence rolling.

 

Yes, no and yes.

Yes, I use diff locked when icy, blizzardy, slow-go conditions. Does not help if only wet. Hauling mail, we proceeded unless road actually shut down. Would just call ahead and explain it'll be a while. Did not carry chains. Indiana/Ohio.

(No longer haul mail, hate nights but money was good. Hourly. Home daily. Very tense, timed runs w/no breathing space. Push, push but legal.)

Differential locked is not for hwy speed. If it's safe enough for hwy speed, you should have lost the diff lock above 15-20 mph. Continue doing wiggle test to confirm steers for sure rolling, not sliding. You can't see black ice but you can feel it through steering (wiggle test) and need to slow down accordingly.

Unlock while rolling can damage drive train. Full stop (or unlock while rolling at steady speed and wheels NOT slipping--edit per KW, see msg #42).

Engage while rolling can damage drive train. Full stop (or engage while rolling at steady speed and wheels NOT slipping--edit per KW, see msg #42).

Starting to shift funny, grindy? Maybe you forgot to unlock diff. Stop, do it now! Never hurt one but... Might have forgotten... I forget now. : 0)

 

Yeah, it depends on the motor too. For a DD15 they recommend using the engine break at 1800-2200 and can sustain 2200 but warn not to take it over 2400 rpm. 2200 is screaming anyway.
On a 10 spd youll hit 2200 around 75 in 9th and 55 in 8th.

 

Wow guess you learn something new everyday. I'll just leave it @ that.

 

You can go down 1000 times too slow. You only go down too fast one time!

As with all of trucking you learn with experience. Odds are you'll run it again and again and again....