Question For Downhill Driving With An Automatic?

Topic 25394 | Page 1

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Joseph I.'s Comment
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I am into driving OTR for 3 weeks. I hauled grain locally for 30 years from the farm but no distance driving, 60 mile round trips max, and always in a 13 speed manual. I am in a Cascadia with an automatic and wondering the how best to handle steep downgrades, especially longer ones with some curves. Do you switch to manual and select a gear or leave it in auto? Use the jake brake from the top or as needed? If using the jake use 1st, 2nd or 3rd position or is that dependent on the steepness of the grade? Do you use the cruise and set it at a slow enough speed?

Thanks for everyone's ideas on the subject. Mostly I am in the Midwest not out in the mountains so just need some input on how to attack downgrades.

OTR:

Over The Road

OTR driving normally means you'll be hauling freight to various customers throughout your company's hauling region. It often entails being gone from home for two to three weeks at a time.

Turtle's Comment
member avatar

Hi Joseph, that's a great question, and an important one.

Your Cascadia should have a decent control feature within the automatic transmission. I believe all of the later models do.

To activate descent control:

At the top of the hill, activate level 2 engine brake, then set your cruise control to your desired speed. That's basically all you need to do. The descent control will raise or lower engine brake levels automatically to keep you at that desired speed. In the case of a flat spot midway down the hill, it'll also apply throttle to maintain your desired speed.

Keep in mind that depending on the weight of your load, you may still need to use your service break as needed. After applying your service break, you'll need to activate cruise control again to reactivate descent control.

I suggest trying it out on a mild grade beforehand, to get used to the functions.

Keith A.'s Comment
member avatar

I run grades in the semi-manual setting in my 12 speed Volvo (auto). Generally you will come down any given grade in the gear you climbed it. So your gear selection and jake break selections depend on:

Weight of your load, (the heavier the slower you're going to go),

The terrain (some of the climbs in the Rockies have 30-35mph curves coming down hills (or slower-- Wolf Creek Pass has you drop to 15-20 for a hairpin or two)),

The road conditions-- it is inadvisable to use the jakes on slick or wet roads as Jake breaks do not apply even pressure to slow the vehicle down, only the tractor,

and the steepness of the grade. Every additional percentage point of grade is another 1ft drop per 100ft and it adds up. At least in my truck each percentage increase means dropping another gear, if you're really playing it safe.

Tractor Man's Comment
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I am in a 2019 Automatic Cascadia. I have traveled back and forth over Donner Pass between Reno and Sacramento almost daily. 75000-78000 gross from Reno to Sacramento and empty on the way back. I ALWAYS switch to manual mode and use the engine brake when going downhill. For the most part 9th gear and the 3 position on the engine brake is sufficient when loaded. When empty, 11th and #3 or sometimes 10th and #2 or #3. It is a learning process for sure. My goal is to be "geared" as such, to have to use the accelerator pedal to briefly disengage the brake to pickup a bit of speed. I use the "safe speed" formula. For example: If I have determined my safe speed to be 45 mph, I choose a gear and engine brake setting that will actually keep me below my safe speed. once I reach 40 mph i will briefly push the accelerator to release the engine brake, get back up to 45 mph, then let the engine braking slow me back down to 40 mph. I rarely use the service brakes when going down hill. You will eventually learn the different gear and engine brake settings for different weights and grades. I hope this helps. As the Colorado story has taught us, SLOWER is better on steep grades. Be safe.

OOS:

When a violation by either a driver or company is confirmed, an out-of-service order removes either the driver or the vehicle from the roadway until the violation is corrected.

Robert D. (Raptor)'s Comment
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My 2018 Cascadia, used to automatically switch the Jake on going downhill 2 mph over my cruise speed but now it has been intermittent with it. But usually I have been applying the Jake going down some the hills and mountains withit in #2 and some times #3. Never in snow or heavy rain.

But it is each individual's comfort level at play. I have an "A" service and "B" service due by the time I get to Little Rock, so I will have them address the Jake coming on after 2 mph over cruise speed.

Raptor

Joseph I.'s Comment
member avatar

"so I will have them address the Jake coming on after 2 mph over cruise speed. Raptor"

Isn't the speed at which the jake "comes on" just a setting that can be adjusted within the menu you control from your left keypad on the steering wheel. Same as you can adjust the following distance and other ACC features?

OWI:

Operating While Intoxicated

Bill R.'s Comment
member avatar

Tractor Man wrote:
I use the "safe speed" formula. For example: If I have determined my safe speed to be 45 mph, I choose a gear and engine brake setting that will actually keep me below my safe speed.
once I reach 40 mph i will briefly push the accelerator to release the engine brake, get back up to 45 mph, then let the engine braking slow me back down to 40 mph. I rarely use the service brakes when going down hill.

Tractor,
Excellent advice. Putting this one in the helpful hint file. I've done the same thing in my personal vehicle, but it has never crossed my mind when thinking over CMV driving.
Bill R.

CMV:

Commercial Motor Vehicle

A CMV is a vehicle that is used as part of a business, is involved in interstate commerce, and may fit any of these descriptions:

  • Weighs 10,001 pounds or more
  • Has a gross vehicle weight rating or gross combination weight rating of 10,001 pounds or more
  • Is designed or used to transport 16 or more passengers (including the driver) not for compensation
  • Is designed or used to transport 9 or more passengers (including the driver) for compensation
  • Is transporting hazardous materials in a quantity requiring placards

OOS:

When a violation by either a driver or company is confirmed, an out-of-service order removes either the driver or the vehicle from the roadway until the violation is corrected.

Tractor Man's Comment
member avatar

Copied and Pasted directly from the CDL Manual:

2.16.4 – Proper Braking Technique Remember. The use of brakes on a long and/or steep downgrade is only a supplement to the braking effect of the engine. Once the vehicle is in the proper low gear, the following are the proper braking techniques: Apply the brakes just hard enough to feel a definite slowdown. When your speed has been reduced to approximately five mph below your "safe" speed, release the brakes. (This brake application should last for about three seconds.) When your speed has increased to your "safe" speed, repeat steps 1 and 2. For example, if your "safe" speed is 40 mph, you would not apply the brakes until your speed reaches 40 mph. You now apply the brakes hard enough to gradually reduce your speed to 35 mph and then release the brakes. Repeat this as often as necessary until you have reached the end of the downgrade.

I have just taken it one step further and tend to rely primarily on the engine braking. Not to say I never use the service brake, just as sparingly as possible. I am always blown away as I follow another truck down a grade, his brake lights on almost constantly, and smoke rolling off of the tandems. The smell is unmistakable. I attribute this to ignorance and/or poor training.

*Before anyone accuses me of being mean by using the word ignorance, if you do not know the definition, look it up!*

smile.gif

CDL:

Commercial Driver's License (CDL)

A CDL is required to drive any of the following vehicles:

  • Any combination of vehicles with a gross combined weight rating (GCWR) of 26,001 or more pounds, providing the gross vehicle weight rating (GVWR) of the vehicle being towed is in excess of 10,000 pounds.
  • Any single vehicle with a GVWR of 26,001 or more pounds, or any such vehicle towing another not in excess of 10,000 pounds.
  • Any vehicle, regardless of size, designed to transport 16 or more persons, including the driver.
  • Any vehicle required by federal regulations to be placarded while transporting hazardous materials.

Tandems:

Tandem Axles

A set of axles spaced close together, legally defined as more than 40 and less than 96 inches apart by the USDOT. Drivers tend to refer to the tandem axles on their trailer as just "tandems". You might hear a driver say, "I'm 400 pounds overweight on my tandems", referring to his trailer tandems, not his tractor tandems. Tractor tandems are generally just referred to as "drives" which is short for "drive axles".

Tandem:

Tandem Axles

A set of axles spaced close together, legally defined as more than 40 and less than 96 inches apart by the USDOT. Drivers tend to refer to the tandem axles on their trailer as just "tandems". You might hear a driver say, "I'm 400 pounds overweight on my tandems", referring to his trailer tandems, not his tractor tandems. Tractor tandems are generally just referred to as "drives" which is short for "drive axles".

OWI:

Operating While Intoxicated

Phoenix's Comment
member avatar

When the engine brake is activated in some trucks the brake lights come on and stay on.. they're easily spotted though, because they don't have smoke rolling off their tires lol.

Anywho, there's something I have trouble with on the hills when my engine brake id engaged... for the most part, I'm good with the engine brake, but occasionally... too often lately cuz I'm learning a new truck.. my engine shoots up to 1800-2000rpms while I'm going down a hill. It's not just when I'm heavy going down a steep grade. Why does it do this? There doesn't seem to be an isolated situation, rather it seems random, and it's very frustrating. I switch to manual and go up a gear and then need to get my speed down cuz now I'm going faster than my safe speed.

Is it my driving skill, or could it maybe the tranny? It does this when upshifting from a dead stop all the way into 7th, then only goes to 1450 for 8th and up. I've tried barely touching the throttle, flooring it, and every inch in between. It's making me feel like I don't know how to drive... and I drive an auto for heaven's sake lol.

Old School's Comment
member avatar
When the engine brake is activated in some trucks the brake lights come on and stay on.

I'm not sure about that. I'm not saying you're wrong Phoenix, I have just never known that was the case. Can anyone verify this?

there's something I have trouble with on the hills when my engine brake is engaged... my engine shoots up to 1800-2000rpms while I'm going down a hill. Why does it do this? it's very frustrating. I switch to manual and go up a gear and then need to get my speed down cuz now I'm going faster than my safe speed.

Phoenix, your engine brake needs the higher RPMs to be effective - that's actually how it works. If you shift up a gear, it loses the RPMs and becomes less effective. Therefore your speed will increase. Higher RPMs are needed to maintain the lower speed. I know that sounds backwards, but that's how the Jake brakes work.

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