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Old 11-17-2021, 04:26 PM   #1
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Driving Mountain Grades without jake or exhaust brakes

Hi yall - new to the forum and seeking advice on driving a Bluebird Skoolie down various mountain grades. We are a 38' rig, ~26000 lbs, Cummins ISB 5.9 with an Allison 4 speed automatic transmission, air brakes (relatively new drums) with recently tuned slack adjusters, but [B]no jake or exhaust brakes.*

Heading thru AZ later this month and will be driving on I17 to Camp Verde up to the Cottonwoods and then back down I17 thru Black Canyon City.* The Mountain Directory Guide says '6% grade for 7 miles" down to Camp Verde and '6% grade for 5 miles' back to Black Canyon City. Do yall have suggestions for safe speeds/gear (2nd or 3rd) to maintain for that length of descent with my rig capabilities and any other strategies for navigating these and future downhills? Any advice will be greatly appreciated. I have heard from a few RVers but wanna hear how the Skoolie community tackles these grades. Thanks in advance.

-Anand

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Old 11-17-2021, 04:46 PM   #2
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Never come down in a gear higher than you went up! If you were in 2nd going up don't start off in 3rd going down. The laws of gravity have very steep fines when broken. You didn't say what transmission you have AT or MT, the MT does better. If you start down in 2nd gear let it run up to about 200 rpm below max up shift speed and brake it down firmly but not a panic stop to about 1500 and then repeat. It won't hurt to start in 1st gear and shift up if you have to use throttle to maintain speed. Just DO NOT start in 4th and then try to slow it down later. Most grades have a max speed posted coming down stay under it with your flashers going and don't let yourself be pushed faster than your control speed by other drivers. I've been on that hill and it is not to be fooled with. Since you are going up first you will know what gear not to go over coming down. Allison's will up shift coming down if you get to close to the up shift speed and then you may need new undies. The fact that you are asking indicates you want to be safe. Have a good safe trip.
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Old 11-17-2021, 05:34 PM   #3
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search the forum. i've written similar threads, so have others.

the problematic transmission is the at545, if you don't have that one, you are in pretty good shape. most transmissions are easy.
the 545 can work fine or... it will slip and give away and you'll run out of control.

if you have the 545, go slower down than you go up. flashers on. if you are going downhill at 55-65mph on a 7% grade, your brakes are worthless. i've caught my brakes on fire a couple of times, trying to come downhill to fast.

its a learning curve of what to do and what not to do.

here in Colorado, slower and controlled is my message.
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Old 11-17-2021, 06:16 PM   #4
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It's already been said twice, here it is a third time - whatever gear you went up, be in that gear or lower going down. With a 4 speed I'd say the same gear should be fine.

As for braking, riding your brakes is what causes them to fail. Therefore, the best approach is to use the engine RPMs to control the rate of acceleration, then when you get close to max RPM or a speed you're no longer feeling comfortable, apply firm not panicked brake pedal to reduce your speed about 10mph. Let off the pedal and the brakes will cool as the engine continues controlling the rate of acceleration again. Also if it's air brakes the air pressure has a chance to recover during this time.

If you pick up speed too rapidly then you were in too high a gear to begin with. As s2mikon said, the laws of gravity have very steep fines. That wasn't humorous wordplay, that's seriously a warning that the price of making a mistake can be your life and those with you or around you. The fact that you're asking ahead of time suggests that you appreciate the gravity (again not a pun) of negotiating grades in a large vehicle. That apprehension is good and will probably be what keeps you alive.

Safe journey!
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Old 11-17-2021, 09:19 PM   #5
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AGAIN, same gear down (or lower) than the one you went up in. Top the hill *start down) at teh slowest speed yo went up and the lowest gear you were in. Keep the speed down by braking down 5-10 mph and then getting off the brakes.



6% isn't horrible but it is enough for you to go too fast real easy. Out here in the West 6% is nothing. Now that 15% downgrade coming out of Mouth Rushmore S Dakota????? That's a B___CH. I went to granny low on my manual or it would over speed the engine of my 7.3.


Slow on a 6% should be no biggie as long as you're in 2nd or 3rd depending on your trans and start with low speed at the top.
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Old 11-24-2021, 05:19 PM   #6
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Posted this before
Proper brake adjustment is just as critical.
Expansion happens.
https://www.sgi.sk.ca/air-brake/-/kn...m-of-your-life
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Old 11-24-2021, 06:08 PM   #7
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Posted this before
Proper brake adjustment is just as critical.
Expansion happens.
https://www.sgi.sk.ca/air-brake/-/kn...m-of-your-life



This is really good info. I had not seen it before, Thanks for reposting.
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Old 11-24-2021, 06:41 PM   #8
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I am new to mountains in my bus. It’s a 34’ Thomas ER with 5.9 Cummins common rail and MD3060 5sp transmission. When I got to the top of the Grapevine I put her in 4th and started out at 30 mph. I planned to stab brake at 45 back to 30. If I found myself braking too much I planned to pull her over and start again in 3rd gear. I was counting on the lock up torque converter.
I ended up having to stab break twice all the way down to Castaic. The bus handled like a dream and I’ve got the confidence now to tackle most anything.
Just keep an eye on your temps.
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Old 11-24-2021, 10:13 PM   #9
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Is there any downside to using transmission to brake as long as RPMs aren't too high? Like does it cause heat or wear on anything? Are there any transmissions that handle better than others? Like a 643 vs 545 or 3060.
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Old 11-24-2021, 10:48 PM   #10
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YouTube STAB BREAKING. LEARN IT AND LIVE ANOTHER DAY
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Old 11-24-2021, 10:52 PM   #11
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Originally Posted by fo4imtippin View Post
Is there any downside to using transmission to brake as long as RPMs aren't too high? Like does it cause heat or wear on anything? Are there any transmissions that handle better than others? Like a 643 vs 545 or 3060.
As long as you don't over speed the engine you are fine. If the Allison is set up properly it will up shift before then anyway. The mt643 or the 3060 is better than the at 545 because of the lock up converter. If you have the Allison with the retarder it is really nice. I have the mtb 643 in mine and it is as good as a jake brake without the noise. You just have to watch the temperature gauge when using the retarder. They can get warm.
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Old 11-24-2021, 11:04 PM   #12
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Be mindful of downhills. Slow going, one gear lower that the one you climbed it in. Rpm’s are super important, keep them in the power zone. That’s not the max rpm but each engine is different, my dt466 trucks do well at 2000-2500rpm. If it starts to climb then I stab break to get the rpm’s -overal speed down to the 2000-2100 rpm range.
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Old 11-24-2021, 11:36 PM   #13
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I remember the Grapevine. Years back I went the grapevine route to get to Rosamond for a race. Going up in the "old Crown" it actually went 25 mph. Going down I held it at 35 - 40 mph and didn't smoke the brakes. The "new Crown" has a jake and 400+ hp. In that case I believe that it would climb the Grapevine at 55 - 60 mph. I would not want to go 55 - 60 mph down the grapevine though.
In northern Cali on I5, north of Redding in the Siskiyou mountains there are some long grades going up and down, some with challenging turns. Their are always signs that state the grade % and distance. Some of these grades don't have an uphill portion first. To me, a 6% grade means 45 mph, 7% grade means 35 - 40 mph. If the stretch of road has runaway truck ramps (like the Grapevine) I take that as good reason to go slower. The steepest grade I ever encountered was 9% on a back road in upstate New York (I was on a Harley at the time). Glad I wasn't in the Crown.


None of what I state is meant to contradict the recent posts to the thread. They are correct. I actually advocate a little slower. If you have horsepower I suggest slower than up the hill even a gear lower.


When I drove the the Grade on I5 coming North out of Dunsmuir in the new Crown I was doing 54 mph at the bottom, 62? at the top (in 4th gear). In the old Crown, the same grade I was doing 18 mph in 1st gear. (one reason I got the new Crown). Big difference in speed between the two Crowns, but still one would need to keep downhill speed about the same between them.


Just my two cents.
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Old 11-25-2021, 02:00 AM   #14
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These are a few pictures from my air brake manual that I found helpful, especially the first one with the brake drum temperatures. I bought one of those laser temperature readers to check the drum temperature for those long or steep downgrades. I didn't do much traveling in the bus this summer so I haven't used it yet.

My manual basically repeats what others have said on here but you can read for yourself in the other pictures.
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Old 11-25-2021, 03:00 AM   #15
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The steepest grade I ever encountered was 9% on a back road in upstate New York (I was on a Harley at the time). Glad I wasn't in the Crown.

10% coming out of Mt Rushmore on SD 244 East. We were pulling a 5th wheel with our F350. In 1st we were accelerating and approaching redline. I stopped in the middle of the road using manually applied full trailer brakes and lots of truck brake. Dropped her into granny low and idled down the hill at about 4 miles and hour.

The toughest interstate grade I'm aware of is 7% for 7 miles. With a few 7% at 4 to 6 miles.
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Old 11-25-2021, 04:16 AM   #16
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In a semi truck I find that it's not the grade or length that's the biggest challenge, it's the curves. I'm not interested in pushing the envelope to see how close to death I can get so I employ all my training and experience to avoid it and one of the things I don't like to do is be trying to control my speed in a curve. I need to be stab braking in the straightaways so that I'm entering the curve slow enough for the curve PLUS the grade. That's tough in some places where it's almost ALL curves. All the more reason to learn it and live it.

I've only taken I-70 west out of Denver once because a lot of trucking companies won't dispatch across that stretch and after driving it once in summertime I understand why. I wouldn't even attempt it in winter and I'm a confident driver.
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Old 11-25-2021, 06:37 AM   #17
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YouTube STAB BREAKING. LEARN IT AND LIVE ANOTHER DAY
yea stab braking works BUT make sure everything is secured and passengers are belted. make sure that nothing can go flying loose and hit the driver in the back of their head
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Old 11-25-2021, 07:55 AM   #18
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yea stab braking works BUT make sure everything is secured and passengers are belted. make sure that nothing can go flying loose and hit the driver in the back of their head
Good advice nonetheless. At least once a day some a-hole cuts me off just to brake-check me and take the exit that's been clearly marked for two miles but you know they had to be first to exit and by the end of the day something in the bunk has found it's way onto the floor.
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Old 11-25-2021, 10:39 AM   #19
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most of us have auto slack adjusters.

these need a few swift 100psi+ brake applications to adjust and be in working order.

Everyday use keeps them working, if the truck sits for a while, you need to check and make sure they adjust and not stuck.

i cut my teeth on I70 downhill into Denver. the thing that tricked me, was that everyone else goes so fast. at 65 or so, i'm lucky to have survived and not made a spectacular, news worthy crash at the bottom of the hill. other have.

ignore other traffic, go slower than you think you need to.

nonlockup TCs like the 545 won't hold you back on steep downhill. its the same as going down in neutral, but with lots of bad noises coming from the transmission.
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