Community Forums

PeteDr · 02-04-2023, 07:05 PM

Each year we cross the Appalachian mountains back and forth at least once on I-40. Going West seems easier on the brakes, and coming East significantly harder. In fact I can smell the brakes getting hot, when maintaining a safe speed, coming East. Thus I am seeking the "best practices" from our mountain driving members. Here are a few questions.

Do you use the "engine brake" feature on the Allison 3000MH transmission? If so, when do you engage it, sitting still or on the fly when needed? Any negative in using this feature? Brake jobs are a lot cheaper than transmission/engine jobs!

Any techniques for managing the hot brake situation, other than what you use in a standalone pickup truck (get on them when needed and off the brakes as the situation allows)? I have not experienced any brake fade, just the smell.

BTW, we tow a 2018 GMC 1500 at 6000 lbs. with our 2019 3709 Ventana LE coach. The coach is well within its GCWR, with empty black and gray water tanks.

Thanks for your input.

RV Driver · 02-04-2023, 07:18 PM

Quote:

Originally Posted by PeteDr

…Do you use the "engine brake" feature on the Allison 3000MH transmission? If so, when do you engage it, sitting still or on the fly when needed? Any negative in using this feature? Brake jobs are a lot cheaper than transmission/engine jobs!…

I use the Jake Brake our coach about 90% of the time we’re on the road. That’s what it’s there for! I have run the exact same route that you have described in this post, and have never touched my service brakes! With the Jake Brake on, you can come down a 6% grade in fifth gear and never touch the brakes.

When you’re on the interstates, just turn it on and leave it on.

I don’t mean to be condescending here, but by asking these questions you have revealed that you really don’t know how to drive your coach. Find someone who can show you first hand how to use that “extra” brake properly. You should be able to drive on Interstate mountain grades anywhere and never smell your brakes. That is dangerous!

bhammond1980 · 02-04-2023, 08:06 PM

When driving in the mountains I use the following methods.
Climbing: I stay in the RH lane, take my time and monitor the engine temp. I also run my transmission in the manual mode so that I can keep the engine RPM near its sweet spot. I try to never lug it.
On the other side: I turn the engine brake on before I make the peak. Mine is a two-stage version that is very effective on the high setting. Again, I stay in the RH lane and normally stay below 45 mph or 50 mph depending on the road, curves and grade. I choose a gear that keeps me within normal engine rpm and use the two stages of the engine brake to control my speed. I rarely touch the brake and when I do it's more of a quick stab instead of riding them. I rarely ever have any brake smell during a decent. I only smell the brakes when someone does something in front of me that requires a quick stop. Most of the time I run with the semi's or slower on the way down.

tmandoug1 · 02-04-2023, 08:35 PM

I hate to stomp on you but you really should know the capabilities of your equipment prior to conducting operations in steep grade situations. You're engine/Jake brake is your go to in those situations. Brakes are poke and jab when needed to usually keep you 5mph slower than the posted speed limit. I hope I didn't misunderstand you......

**TonyDi** · 02-04-2023, 08:51 PM

Your engine brake is your best friend in the mountains. If I'm driving in mountainous areas I keep the engine brake engaged. I do not turn it on in flat terrain. I don't want the engine brake engaging every time I decide to coast. With the location right next to you it's easy to engage. JMHO.

Dennis C. · 02-04-2023, 09:10 PM

I switch my engine brake to the “on” position whenever I am on an interstate highway, and whenever I am in the mountains. It’s a wonderful tool. The engine brake combined with judicious “stab braking” when descending a steep grade will keep your speed under control and keep your brakes cool.

Dutch Star Don · 02-04-2023, 09:41 PM

Is it an engine brake or exhaust brake.....the Newmar brochure doesn't say.

BobGed · 02-04-2023, 10:12 PM

I may be wrong, and if I am I'm sure someone will be along to point it out, but I don't think you have an engine brake in your Ventana LE. I think you actually have an exhaust brake, and quite frankly they're not as efficient in holding a coach at a steady speed descending a steep downhill as an engine brake as the previous posters described.

That's what I have in my coach, and I live in the west where we have a lot of steep mountains. Even with the EB active I have to do a lot of manual shifting and stab braking to control my speed on steep descents.

First of all I have my exhaust brake parameters set so it activates when I step on or tap the service brake pedal, and deactivates when I step on or tap the throttle pedal. This allows me to control my exhaust brake without having to take my hands off the steering wheel and hunt for the brake switch.

As I approach a summit I will manually gear down to whatever gear I think is appropriate for the upcoming descent. If I'm not sure I will always select a lower gear as it's much easier to upshift than it is to downshift while descending. I will also tap my service brake to active my EB.

The Allison transmission will automatically upshift to protect itself and the engine. If I start picking speed I will control brake (hard on the service brake for a count of 5, then release). I usually try to do this prior to the transmission automatically upshifting. It may be necessary to do this several times while descending. Just make sure to allow time between applications to let the brakes cool.

You should never smell your brakes. Let your transmission and exhaust (or engine) brake assist to get you safely down the mountain. It's almost impossible for a driver to damage them.

PeteDr · 02-04-2023, 10:16 PM

Let me as the OP just get us on the right course outline. So far the responses have been more at the grammar school level. My intent is to discuss this at the PhD level. So if you choose to participate, please self evaluate your credentials/knowledge before participating. Some might start on a simple level, learning the difference between a JAKE BRAKE and an ENGINE BRAKE. The 360HP/Allison 3000MH definitely does not have a JAKE BRAKE.

With that written, let me expand on my interest. Friction brakes are simply tasked with converting rotational energy to heat using friction and a sacrificial media of brake pads or shoes. We all know this and Freightliners projects that the life expectancy of media is about 200K miles on the chassis and coach I have. Bottom line the brakes will outlast the coach, under anticipated usage. So using them to come over some mountains occasionally, not a problem. If you do manage to get to the point of needing new pads or shoes, not a big expense.

But, the 360 Cummins/Allison 3000MH offer an alternative. Use the provided engine brake and eliminate some wear and smell from the friction brakes. Now we are getting to the questions I intended to raise. Lets start with a fact, “Energy cannot be created or destroyed (only change form).” is a common paraphrase of the law of conservation of energy. So by using the engine brake, less heat at the friction brakes, necessitates increased heat somewhere else. The only two candidates are the engine or transmission or both. Does anyone understand and able to explain this phenomena? Simply stated where does the heat go and what is the negative impact of the heat rise? I would much rather create additional stress on the friction brakes than create reverse torque on the gears, bearings, clutches, etc. of the engine and transmission. Ever wonder why 18 wheelers all use Jake Brakes? Thus my original observation, brake jobs are a lot cheaper than transmission/engine jobs! Is there a trade off here, and what is it?

PeteDr · 02-04-2023, 10:22 PM

My 2019 3709 Ventana LE definitely has an engine brake. I have played with it underway and it works as expected. Not sure I like the feature, as it strikes me as a cheap substitute for a jake brake, with possible engine/transmission downside.

BobGed · 02-04-2023, 10:41 PM

Maybe we should start at the grammar school level so we're all on the same playing field.

When you can smell your brakes that means they are overheating. At some point because of that overheating they will stop functioning. That is why most major highways with steep descents have runaway ramps.

A Jake (aka Jacobs) brake is an engine brake.

How did you determine you have an engine brake and not an exhaust brake? Does your switch have one ON position or more than one?

Mr. T · 02-05-2023, 07:03 AM

Quote:

Originally Posted by Dutch Star Don

Is it an engine brake or exhaust brake.....the Newmar brochure doesn't say.

My switch says engine brake

Dennis C. · 02-05-2023, 07:37 AM

My 2018 Ventana has a switch that is labeled “Engine Brake”. However, that switch activates an exhaust brake. It is very effective when used as intended.

I’ll refrain from further commentary as I realize my experience doesn’t constitute “PhD level” feedback. To the OP, I suggest that you reach out to the engineering departments of the various companies that manufacture the components in the engine, transmission, and braking systems. Perhaps they can provide you with the information that you seek. The contributors to these forums generally provide responses based on their personal experiences and are not prepared to discuss things like the law of conservation of energy. Your questions are unlikely to be answered to your satisfaction on these forums.

RV Driver · 02-05-2023, 08:16 AM

I’ll do my best to get up to the Phd level here.

It does not matter whether you have a Jake (compression) brake or an exhaust brake, they both do the same thing. They offer an additional form of braking, using the engine. A “Jake Brake” is also correctly called a “Compression Brake.” It changes the timing of the opening of the exhaust valve to release the energy of compression.

With the Jake Brake OFF, the energy used to compress the air on the engine’s compression stroke is returned when that compressed air pushes the piston back down. No fuel is injected into the cylinder during this time because you are coasting with your foot off the throttle. But because there is no throttle valve in the air intake, as there is in a gasoline engine, no vacuum is created in the engine when your foot is off the throttle. Consequently no braking effort is developed.

With the Jake Brake ON, the exhaust valve opens just as the piston reaches the top of the compression stroke. All the energy used to compress the air is released to the atmosphere. It’s a rather explosive release, which is why an un-muffled Jake Brake can be very loud. Because we are essentially “wasting” energy by releasing compressed air to atmosphere, no additional heat is generated.

An exhaust brake is much simpler, but also less effective. This type of brake is just a flapper valve in the exhaust that closes off the exhaust stream. The resulting pressure rise in the engine increases the rotational drag in the engine and provides some braking effort. There may be some additional heat generated when using an exhaust brake, but it is minimal.

BOTH of these brakes are an absolute necessity when driving in the mountains. You should never smell your brakes. I’ve driven our coach over 100,000 miles all over the US, including the route you mentioned. I have never, ever smelled my brakes getting hot because I rarely have to use them. The Jake Brake, combined with the natural wind resistance of the very un-aerodynamic shape of a motor home, keeps the speed in check without using the service brakes.