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Old 08-19-2013, 07:40 PM   #15
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Gear Up is the Gear Down

Whatever gear you use going up the hill, is the gear you use going down the hill, and use your engine brake. Don't be in a hurry going up, and don't be in a hurry going down.

Brakes catch on fire when you release them. That is when the oxygen can get to them. If you lose it with the transmission and engine brake, get on the wheel brakes. You can buy new shoes, or you can buy a new motorhome after it burns up.
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Old 08-19-2013, 07:49 PM   #16
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but what is the rule of thumb for when high, when low? Would this mostly be dependant to grade? Would high be the best for city limits (if legal) when approaching an abundance of intersection lights.

bill
The low setting uses three cylinders as a compressor to slow you down and the hi setting kicks in all six. I decide which to use based solely on how much "stickum" I want to apply at the time. My guess is that 90% of the time the low setting gets me by.

I would think that the high setting would be better for city driving and I don't think there would be a legality issue.

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Whatever gear you use going up the hill, is the gear you use going down the hill, and use your engine brake. .
I've read this rule of thumb for a long time and I'm afraid I still don't understand it.

I get the whole matching of gears going up and down when driving a gasser. But, when using the engine brake, the Allison immediately requests 2nd gear and tries to slow you down until it can accomplish downshifts to get there. That is, unless the Allison has been programmed to seek a different gear but that's not something done on the fly.

Can someone 'splain it to me?

Rick
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Old 08-19-2013, 08:00 PM   #17
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IF YOU HAVE A DP AND USE A PAC BRAKE READ THIS LINK ON HOW TO USE IT.
The gearing down to 2nd gear is explain in link for a DP.
That's what the OP has.
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Old 08-19-2013, 08:40 PM   #18
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Folks I'm not going to get into an argument on braking techniques. If you pump the brakes hard and constantly you have a greater chance of overheating. I'm not saying to ride the brakes all the way down the mountain, but if you must apply the brakes it's better to do less often for longer periods. This is IMHO and 20+ years driving big rigs.
Simply put, dont ride your brakes on a down slope as they will overheat.
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Old 08-19-2013, 09:17 PM   #19
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If you're going down a hill , using no brakes, and only your engine brake is bringing you down to 2nd gear, and that is too slow for you, you either have to give it some throttle or maybe the hill is not long or steep enough that you even need the engine brake. The idea is to use the gear that holds you back to the speed you feel is safe with the minimum amount of braking. I don't depend on the transmission programmer to know what's right for me , especially since he may have never been in the mountains. That's why it is MY responsibility to keep my vehicle under control, not the computer progammers'.
Learn the speed your MH goes in each gear at the RPM you are comfortable with. A good way to learn this is to lock it down in first gear and manually shift it up one gear at a time shifting at maximum rpm you are comfortable with.
When going down a mountain It's possible that one gear is slower than you'd like to go but the next gear up is too fast and requires too much braking, in that case use the lower gear.
I drive trucks and plow snow in CO and I always use the engine brake, I give it some throttle to keep the eng brake from coming on when I don't want it, but it could use a little more fuel that way.
I have heard the saying " don't use the engine brake in slippery conditions", I don't adhere to that because the engine brake is usually smoother than applying the foot brake, however, I guess it's possible to skid the rear tires, with a sudden downshift on a lighter vehicle with the engine brake on icy roads. That's another reason I like to manually choose when to downshift.
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Old 08-19-2013, 09:46 PM   #20
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......but if you must apply the brakes it's better to do less often for longer periods.....
Freightliner recommends braking 5 seconds, cooling 5 (or more) seconds. I've found that to work pretty well.
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Old 08-19-2013, 11:42 PM   #21
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Folks I'm not going to get into an argument on braking techniques. If you pump the brakes hard and constantly you have a greater chance of overheating. I'm not saying to ride the brakes all the way down the mountain, but if you must apply the brakes it's better to do less often for longer periods. This is IMHO and 20+ years driving big rigs.
If I was laying in the bunk of a sleeper cab coming down a mountain with 80,000 pounds gross weight I want you in the driver seat harleychief! Your the only one who has given the right answer.
Many years ago, 50 to be exact, before engine brakes were all that popular we had to descend mountain grades with only what the engine would hold back and your service brakes. The proper way to descend was to start at the top at a speed you thought you could maintain while holding no more than 5 pounds air pressure on your service brakes. Yes we had an air gauge which showed brake pressure. Unfortunately we don't have those gauges in our MH's. If you started to build to much speed then you had to apply more brakes just long enough to slow down to a speed where you could drop another gear then go back to 5 pounds brake pressure. You could hold that pressure all the way down. You never "fanned" or "stabbed" your brakes on and off. The guys who did that were the ones who never made it to the bottom with the shiny side up. This procedure worked for me for 40 years accident free driving.
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Old 08-20-2013, 12:37 AM   #22
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I agree with Harley chief and Rotten Red.

Another thought is to subtract the degree of down slope from 10 and start down the hill in that gear. Turn on jake brake or exhaust break and enjoy the ride down.

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Old 08-20-2013, 08:26 AM   #23
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seems like this has spurred a lot of debate! Thanks for all the advice and shared experience. The campground we are checking out of this weekend has a short, steep hill that I have to ascend and descend so I am going to experiment here on my way back to my storage lot this Sunday. I want to see if i can hold my speed without the service brakes and with the exhaust brake only (cresting the hill at the same speed I want to descend). Is the exhaust brake the 'pac brake'?
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Old 08-20-2013, 08:40 AM   #24
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Lots of conflicting advice here and I imagine the OP isn't much wiser than when he asked the question.

Do a search on the web for "snub braking technique" first and see if that answers your questions. Technique will change depending on whether you have an auto or manual transmission, but one thing is certain - on steep grades the Allison transmission isn't the slightest bit interested in getting you to the bottom safely. If the engine overspeeds, it will change up to protect the engine. You need to take control by manually downshifting and using that plus engine or exhaust brake PLUS snub braking (meaning neither light constant brake application NOR short hard jabs) plus a bit of smarts to get to the bottom safely.
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Old 08-20-2013, 01:21 PM   #25
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Down Hill RPM's ??

Here is kind of a related question.

When going down hill using the engine brake, I have always wondered what kind of RPM's the engine should get up to. I know the transmission will protect it from over-speed ... but it sure sounds like it is revving up and I feel like I need to use the brakes to slow it down a bit.

Is there any kind of a red-line RPM I need to keep in mind just to play it on the safe side? Hope that question makes sense. I'm just a Florida boy with no hills!

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Old 08-20-2013, 01:30 PM   #26
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Technique will change depending on whether you have an auto or manual transmission, but one thing is certain - on steep grades the Allison transmission isn't the slightest bit interested in getting you to the bottom safely. .
Great point. Allison is programmed to take care of the engine's safety... not yours!

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Is there any kind of a red-line RPM I need to keep in mind just to play it on the safe side? Hope that question makes sense. I'm just a Florida boy with no hills!

Steve
Assuming you're talking about a DP with an Allison, it might vary but 2300/2500 is probably the range where the tranny will upshift.

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Old 08-20-2013, 04:31 PM   #27
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If it does upshift (an it is a bit disconcerting when it does if you don't know about it) then you are likely to be in a runaway situation that requires definite action to get it under control - firm braking to get the speed back well below what it was so the transmission can drop down a gear lower than it was and then go back to the snub braking to keep it under control at that lower speed.
If you were riding the brakes instead of snubbing, then it is possible that the reason for the overspeed is your brakes have failed from overheating (and yes, that can happen to disc brakes too.)

Often hear people complaining that they switched the engine brakes on and nothing seemed to happen. Usually when they come over the top of the hill at 60 and expect the auxiliary brakes to work miracles. Solution is to come over the top slower so the transmission will downshift when the auxiliary brake cuts in and the resulting higher engine revs give more "braking cycles" per foot (yes, highly technical description I know) so braking power is higher than if it were still in 6th gear at lower revs. If it can't downshift then it is up to the driver to brake to a speed where it can downshift and that is where the "smarts" come in to it.
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Old 08-20-2013, 05:01 PM   #28
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If it does upshift (an it is a bit disconcerting when it does if you don't know about it) then you are likely to be in a runaway situation that requires definite action to get it under control - firm braking to get the speed back well below what it was so the transmission can drop down a gear lower than it was and then go back to the snub braking to keep it under control at that lower speed.
If you were riding the brakes instead of snubbing, then it is possible that the reason for the overspeed is your brakes have failed from overheating (and yes, that can happen to disc brakes too.)

Often hear people complaining that they switched the engine brakes on and nothing seemed to happen. Usually when they come over the top of the hill at 60 and expect the auxiliary brakes to work miracles. Solution is to come over the top slower so the transmission will downshift when the auxiliary brake cuts in and the resulting higher engine revs give more "braking cycles" per foot (yes, highly technical description I know) so braking power is higher than if it were still in 6th gear at lower revs. If it can't downshift then it is up to the driver to brake to a speed where it can downshift and that is where the "smarts" come in to it.
Well said.
It all starts at the TOP of the hill. You need to have your speed in check there because once you start gaining momentum down the hill you are likely going to smoke the brakes trying to get it under control to the point where the transmission will downshift if you are going too fast at the top.
My moto is, "Don't start down the hill any faster than you came up". AND, use the Snubbing Technique. Enjoy the scenery.
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