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Old 10-01-2016, 10:11 PM   #1
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How to manage brake systems on long downhills.

We are about 1/3 through a six week loop of the Southwest, Colorado Plateau and Continental Divide. The downhill from Leadville to Golden, in Colorado, was a lot tougher than the uphills until I took better advantage of trailer brakes and TV downshift features. Fortunately it was daylight and dry. Our 2012 F150 EcoBoost 4x4 is well equipped with transmission, stability, and trailer brake controllers. And the 22 ft Safari with a rear kitchen has new brakes and a reinforced frame (curbside had cracked 1/3 through). I have RV'd about 46 years but simply haven't had a lot of experience with long steep grades. Perhaps those of you with experience in such conditions would explain in some detail the ways to take FULL advantage of all these marvelous features.

IMHO, in most TV discussions, all too often we tend to get the tail on the wrong end of the dog. It's not ALL about hauling ass uphill, you gotta come down again, and braking systems are not given the attention they deserve.

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Old 10-01-2016, 10:46 PM   #2
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Low speed, low gears, brake controller set to favor trailer brakes over truck brakes, shift down and let the engine rpm go up for best engine compression braking, brakes applied at intervals rather than steady to control speed, and don't let the speed increase too much before attempting to slow it. The trailer's drum brakes will overheat and fade if applied steady or too much on long downgrades. If you're not familiar with long steep and/or curving downgrades, take another route until you know what you're doing.
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Old 10-01-2016, 11:29 PM   #3
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You'll find a lot of folks will say if you use the brakes at all you're doing it wrong. You use a gear that holds the whole rig with out needing to touch the brakes.
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Old 10-01-2016, 11:36 PM   #4
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Originally Posted by NevadaGeo View Post
You'll find a lot of folks will say if you use the brakes at all you're doing it wrong. You use a gear that holds the whole rig with out needing to touch the brakes.
Maybe with an exhaust brake...
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Old 10-02-2016, 02:03 AM   #5
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Keep in-mind that while travelling down-hill, even with engine-braking in lower gears...the trailer is trying to "push" the Tow Vehicle. Going straight doesn't pose too great a problem.
But...When a curve comes up, the trailer tries to push the rear axle of the TV to the outside of the curve. All you need now is a little loss of traction on those TV rear wheels and you've got a really nice jack-knife/roll-over possibility.

It might be helpful to remember that entering a downhill curve might be a good time to consider a little application of trailer-braking if things get dicey, and going downhill in wet-weather is a really bad idea if it can be avoided.

I should add that I plan to replace the OEM drum brakes as soon as possible with disc brakes to avoid the drum brake's tendency toward heating and fading.
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Old 10-02-2016, 03:48 AM   #6
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As someone who tows more in inclement weather than good weather exhaust brakes are great but there no substitute for proper speed and braking. Yes I use my exhaust brake lots in terrible weather but I combine it with excellent tires and four wheel drive. The really important part is using the service brakes coming into the turn aka truck and trailer brakes. Don't use one more than the other try to find a nice balance of the two.
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Old 10-02-2016, 08:40 AM   #7
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When one lets off of the accelerator pedal, a gasoline engine restricts air flow and provides braking force. A diesel engine controls power by regulating fuel and does not restrict air flow. When an exhaust brake is added, it restricts air flow in the exhaust and provides essentially the same function as the butterfly valve in a gasoline engine's air intake. Properly managing the gear and speed with a gasoline engine can provide braking similar to that of a diesel with an exhaust brake.

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Old 10-02-2016, 09:00 AM   #8
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Quote:
Originally Posted by Al and Missy View Post
When one lets off of the accelerator pedal, a gasoline engine restricts air flow and provides braking force. A diesel engine controls power by regulating fuel and does not restrict air flow. When an exhaust brake is added, it restricts air flow in the exhaust and provides essentially the same function as the butterfly valve in a gasoline engine's air intake. Properly managing the gear and speed with a gasoline engine can provide braking similar to that of a diesel with an exhaust brake.

Al
I disagree with statement gas engine will brake same as diesel engine. First new gas are injected not butterfly carbs, second I don't like diesel in pu but I have driven many diesel trucks and exhaust brake [aka] as jake brake will slo much more than gas eng. even w/foot off gas and lowest gear, will still have to tap brakes to control speed.
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Old 10-02-2016, 09:16 AM   #9
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On Rt. 70 heading east towards Denver there's a downhill run that takes the big rigs down to 25 MPH. Now that's a serious downhill when they show speeds like that. I found it comfortable in our Dodge 3500 diesel towing a 30' AS, no engine brake at 35 MPH. Our new truck has a factory installed exhaust brake but it is not the end all answer. On long upgrades I have no problem keeping the posted speeds but often will stop and take a break at the top, if there's a pullover area. Then attack the downhill at what I feel is a slow controlled speed with minimum braking. Going slow here is your best friend.
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Old 10-02-2016, 09:36 AM   #10
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I disagree with statement gas engine will brake same as diesel engine. First new gas are injected not butterfly carbs, second I don't like diesel in pu but I have driven many diesel trucks and exhaust brake [aka] as jake brake will slo much more than gas eng. even w/foot off gas and lowest gear, will still have to tap brakes to control speed.
I'll have to admit I don't have any experience with direct-injected engines, but the throttle body and multi-point fuel injected gasoline engines I am familiar with have a butterfly valve in the air intake, a throttle position sensor to determine where the valve is set, and a mass airflow sensor to determine how much air the engine is taking in. Everything I can find about direct injected systems only mentions moving the injectors from the intake manifold to the cylinders. Maybe someone else can chime in, but as far as I can tell, fuel injected engines still provide engine braking.

You can test this hypothesis by putting the transmission in a low gear and accelerating to substantial RPM and taking your foot off of the accelerator. I suspect you'll experience significant braking.

That said, a diesel engine (with an exhaust brake) will probably provide more braking due to the higher compression ratio.

Al
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Old 10-02-2016, 09:44 AM   #11
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I think the main reason that a diesel engine has more braking ability is the fact that it has a much higher compression ratio. If both engines have the same displacement, the one with the higher compression will allow more braking effect.
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Old 10-02-2016, 10:23 AM   #12
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We have a Ford 6.7 diesel with exhaust braking. My son has a 2009 Dodge also with exhaust braking. I have never towed our AS with his Dodge but ( my opinion here ) is that the Dodge exhaust braking seems to be more aggressive than that on my '15 Ford. I'm not complaining about the Ford but if it could be adjusted to work a little more aggressively I would be happier but in combination with the 6 sp transmission it seems to do pretty well.
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Old 10-02-2016, 12:06 PM   #13
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I'll have to admit I don't have any experience with direct-injected engines, but the throttle body and multi-point fuel injected gasoline engines I am familiar with have a butterfly valve in the air intake, a throttle position sensor to determine where the valve is set, and a mass airflow sensor to determine how much air the engine is taking in. Everything I can find about direct injected systems only mentions moving the injectors from the intake manifold to the cylinders. Maybe someone else can chime in, but as far as I can tell, fuel injected engines still provide engine braking.

....

That said, a diesel engine (with an exhaust brake) will probably provide more braking due to the higher compression ratio.

Al
There are different approaches on air management with different direct injected gasoline engines. My BMW N54 engine had a throttle butterfly. Other BMW engines later moved to no throttle butterfly, instead using variable intake valve control. Some kept the butterfly but only used it in certain operating modes, such as cold start. More efficiency can be had by eliminating the butterfly, but it brings an additional level of complexity.

Engine braking on a gasoline engine comes from the pumping losses, so the work it takes to pump air through the engine produces the braking effect. More restriction, then there is more braking effect. And there are still friction losses due to the rotating components, unconnected to the injection design.

The braking effect isn't related to the compression ratio unless you have an engine brake that controls the valves, changing their operation under braking. It takes energy to compress the air in the cylinder on the compression stroke. And then, since the engine valves are normally closed, that energy is recovered on the power stroke. Think of it like a spring being compressed and relaxed.

It is important to separate two different types of diesel brakes: an exhaust brake, which creates restriction in the exhaust (like a choke) and an engine compression brake, which changes valve operation to utilize engine compression as a retarder, then exhausts it out, often creating that loud engine retarder noise. The terms are often confused.

Good overview here

https://en.m.wikipedia.org/wiki/Comp...e_engine_brake

Jeff
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Old 10-02-2016, 12:10 PM   #14
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Keep in mind the same gear up as down. Our experience with long steep down grades out there a few months ago. Approaching a down grade slow down and down shift before the beginning of the down grade. More down shifting will probably be necessary. In one particularly long and steep down grade in Utah we were down in first and still accelerating at 25 mph. Now, with the breaking I applied brakes periodically alternating the trailer brake (controller) and the truck alternately and when necessary both at the same time. Not technical but it worked for us. Keep in mind slow and don't let the trailer push you when going into a down hill curve. These were anxious moments.
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