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Old 02-17-2013, 03:48 PM   #15
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Quote:
Originally Posted by Clayobx
In our coach with the 450 ISL the brake is a retarding system. The coach is new and I admit I don't know all the answers. I believe it retards the transmission? Therefore I would not use it all times. One other thought the exhaust brake will effect the toad braking system and most likely cause very premature failure if you have a toad braking system. Just read several post and PDF's from road master noting this issue. We have the Invisibrake system. In many states you are lawfully required to have an auxiliary braking system while pulling. However we most certainly use it climbing and descending the mountains. Look forward to further post!
More than likely your VG turbo is also functioning as an exhaust brake. It will also select a lower gear, generally 2nd or 3 rd, when it is activated. Allison does offer a transmission retard system but the only coach builder I'm aware of who uses it is Foretravel. It usually has a "joystick" controller that determines how strong the deceleration is. The VG turbo acts just like a conventional "PAC" brake with an on/off switch.
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Old 02-17-2013, 06:25 PM   #16
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On an ISL that is probably a full Jake brake. The full Jake brake is internal in the engine, and it works in conjuntion with the Allison trans. It should not effect your toad brakes at all. It is no different than stepping on your brake peddle. Some of the earlier ISL engines had an exhaust brake rather than the full Jake Brake. The operation is basically the same and will not damage your engine or transmission or cause premature wear on them. Your toad brake if set up right will operate in conjuntion with whichever you have. Hope that helps.
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Old 02-17-2013, 08:18 PM   #17
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The weigh station was in Maryland and I did stop.

I took this from a doc from CAT on gas mileage published in 2006:
An exhaust or compression brake does not lower the fuel mileage (MPG) when used for controlling vehicle speed on steep grades or to assist in stopping the coach. Keep in mind that best fuel mileage is achieved when “coasting” as much as possible before using any type of brake to bring the vehicle to a stop.

In moderate rolling hills, brake usage can materially reduce fuel economy (MPG). In rolling hills, best fuel economy is achieved by turning the exhaust or compression brake “OFF”. The vehicle accelerates on descent and decelerates on the climb, but will not downshift as often or spend as much time at wide open throttle to maintain the desired cruise speed. On a downhill, let the mass of the heavy vehicle provide most of the acceleration horsepower and crest the next hill with minimum throttle. Most drivers can achieve better fuel economy by using the cruise control rather than taking over the throttle position management task.


It would seem to me if you only want to coast while determining if you need to brake (looking at traffic changes, slight down hill, etc) and it turns out you don't, with the exhaust brake on, you are braking and not coasting therefore affecting gas mileage.
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Old 02-17-2013, 08:21 PM   #18
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Quote:
Originally Posted by jrgreen View Post
The weigh station was in Maryland and I did stop.

I took this from a doc from CAT on gas mileage published in 2006:
An exhaust or compression brake does not lower the fuel mileage (MPG) when used for controlling vehicle speed on steep grades or to assist in stopping the coach. Keep in mind that best fuel mileage is achieved when “coasting” as much as possible before using any type of brake to bring the vehicle to a stop.

In moderate rolling hills, brake usage can materially reduce fuel economy (MPG). In rolling hills, best fuel economy is achieved by turning the exhaust or compression brake “OFF”. The vehicle accelerates on descent and decelerates on the climb, but will not downshift as often or spend as much time at wide open throttle to maintain the desired cruise speed. On a downhill, let the mass of the heavy vehicle provide most of the acceleration horsepower and crest the next hill with minimum throttle. Most drivers can achieve better fuel economy by using the cruise control rather than taking over the throttle position management task.


It would seem to me if you only want to coast while determining if you need to brake (looking at traffic changes, slight down hill, etc) and it turns out you don't, with the exhaust brake on, you are braking and not coasting therefore affecting gas mileage.
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Old 02-17-2013, 08:27 PM   #19
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I usually run with the exhaust brake on all the time. I feather the throttle if I want to coast. Our exhaust brake works just fine with the cruise too. If the exhaust brake comes on when on cruise it does not shut it off.
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Old 02-17-2013, 09:15 PM   #20
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This thread is about EXHAUST Brakes not ENGINE Brakes. They are two totally different braking systems with totally different characteristics.

If your coach has an Engine Brake please don't confuse the issue and discussion regarding Exhaust Brakes.

Just my opinion.

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Old 02-17-2013, 09:52 PM   #21
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I have an '05 Journey with an exhaust brake. Does anyone know if I would benefit by installing a Pacbrake? Or is the stock exhaust brake the same?
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Old 02-17-2013, 10:01 PM   #22
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Only use as needed when going down long hills. Brakes are cheaper to replace than a motor or tansmission.
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Old 02-17-2013, 10:23 PM   #23
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I don't have a MH but I do have & use an EB. I had it istalled when the PU had 50 miles on it. It now has 90K+. I still have about 50% lining on the brakes. I turn it on when I shift from 2nd to 3rd and turn it off just before I stop. I don't like or use the cruise but if I did I would have to turn off the EB. It has a simple micro switch under the throttle pedal and an on/off switch on the gear shift (manual 6 speed). I like that the EB comes on when my foot leaves the petal. As others have said, I feather the pedal when I want to "coast". Years ago I was in a fire Dept that had a machine that would tell how long it took you get your foot from the throttle to the brake.The best any one could do was 3/4 sec. That is almost 70' @ 60mph. I would hate to think what my time is now 40+ years later. A few years ago I hauled a tractor ( GCW of about 25K) from E Wa. over Blewett Pass in the Cascades. I pulled the east side @ 50 in 5th gear and EB held 50 in 5th gear coming down the W side. I use it all the time, loaded or empty.
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Old 02-18-2013, 07:50 AM   #24
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Thank you Steve, thank you Slickest1' for the technical insight.
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Old 02-18-2013, 08:02 AM   #25
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I have an '05 Journey with an exhaust brake. Does anyone know if I would benefit by installing a Pacbrake? Or is the stock exhaust brake the same?
May I suggest that you open up the engine cover and look at your existing Exhaust brake to see who the manufactured it. Also, you should look up what the lubrication maintenance schedule is and follow it with routine maintenance. Otherwise, it may not work when you need it the most.

Exhaust Brake will be on the roadside close to the turbo.

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Old 02-18-2013, 08:18 AM   #26
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I am gonna disagree with the above post
I just think that the switch will make it easier to manage not just the accelerator but the rig as a complete unit. I think the BS statement above is a little over the top, don't you think?
You still haven't mastered using the fuel pedal to make the MH coast when you want.

May take you a little longer then one trip to practice that. Then no switch will be needed.

IMHO the what you call(BS) statement above yours, is NOT a little over the top. It is right on.

For over 10 years I leave mine on 99.5% of the time. No problem making it coast when wanted. A average of 10.2 MPG, I can live with that using a Exhaust brake.
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Old 02-18-2013, 09:52 AM   #27
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Originally Posted by jrgreen View Post
The weigh station was in Maryland and I did stop.

I took this from a doc from CAT on gas mileage published in 2006:
An exhaust or compression brake does not lower the fuel mileage (MPG) when used for controlling vehicle speed on steep grades or to assist in stopping the coach. Keep in mind that best fuel mileage is achieved when “coasting” as much as possible before using any type of brake to bring the vehicle to a stop.

In moderate rolling hills, brake usage can materially reduce fuel economy (MPG). In rolling hills, best fuel economy is achieved by turning the exhaust or compression brake “OFF”. The vehicle accelerates on descent and decelerates on the climb, but will not downshift as often or spend as much time at wide open throttle to maintain the desired cruise speed. On a downhill, let the mass of the heavy vehicle provide most of the acceleration horsepower and crest the next hill with minimum throttle. Most drivers can achieve better fuel economy by using the cruise control rather than taking over the throttle position management task.


It would seem to me if you only want to coast while determining if you need to brake (looking at traffic changes, slight down hill, etc) and it turns out you don't, with the exhaust brake on, you are braking and not coasting therefore affecting gas mileage.
You can only "coast" so much before your speed becomes excessive. When it does, then what? Mash the foot valve? (Results in excessive brake wear and tear) Hit the EB? (Results in excessive engine wear and tear) Do both?

BTW, there is a reason that cops sit at bottom of hills.
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Old 02-18-2013, 10:42 AM   #28
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You can only "coast" so much before your speed becomes excessive. When it does, then what? Mash the foot valve? (Results in excessive brake wear and tear) Hit the EB? (Results in excessive engine wear and tear) Do both?
To much taking sensible advice to extremes. Nobody is suggesting heading down a long steep incline in what is effectively 'angel gear', or letting speed build up to 20% above legal, but what a few are suggesting is using fundamental laws of physics to save a lot of wear and tear when driving on flattish terrain that is continuously undulating. Slavish adherence to the speed limit by accelerating up a slight incline and braking down a slight incline - which is what cruise control effectively does - or exacerbating that by using auxiliary braking - is just not sensible driving technique because it is using extra fuel and subjecting the drive train to extra stress for no good reason.

Many years ago in Australia they used to hold fuel economy "races" (with an on-board observer who disqualified you if you exceeded the speed limit even briefly) over several hundred miles and the surprising thing that came out of it was there was nothing much you could do on dead flat roads to get an advantage, but in undulating terrain, a canny driver could do far better by allowing the speed to rise and fall than by maintaining a set speed.
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