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Old 04-29-2014, 08:12 AM   #29
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Here's a decent explanation of an "Exhaust Brake":

HowStuffWorks "Exhaust Brakes"

And yes, they DO develop back pressure in diesel engines.
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Old 04-29-2014, 09:57 AM   #30
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I am a new Alpine owner and have been following this thread since braking is very important. Even though previous owner had owned this coach since new, he was not very knowledgeable about its function.

The Exhaust/Engine brake switch has 2 settings. Switch up, off in the middle and switch down. I have left the switch rocked up pretty much all the time. Mine appears to shift the coach into 4th gear once the speed gets below 55MPH, so it sounds like what other are seeing. But to really slow down the coach to slower speeds, I must use the brake pedal when I think the exhaust/engine brake could be more effective.

To make the exhaust/engine brake more effective, do I need to downshift transmission manually? or will having the transmission reprogrammed to pre select 2nd allow it to work automatically starting at 4th , then 3rd and then 2nd?

Also, what does the switch do when rocked to the bottom position. It seems to add some braking, but very little.
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Old 04-29-2014, 10:14 AM   #31
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If your engine is 8.9l then you have the optional ISL engine (the ISC was standard that year). So you have the Jake (compression) brake and do not have an exhaust brake (PAC brake). You have 2 positions on your brake switch because the Jake has high and low settings, so you will notice the difference. Personally I would leave preselect to 4 and manually shift to lower gears if needed.
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Old 04-29-2014, 10:17 AM   #32
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JeepPuller,

The very first thing you need to find out is whether you have an Exhaust Brake or an Engine Brake. They are TWO very different animals that function completely different.

I have posted that so many times that my fingers are getting almost was too short to type.

Have you read the LINK in the previous post made by bcbowers? There are 7 pages of valuable information on both exhaust brakes and engine brakes.

Once you have done that then you will know what function your switch provides.

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Old 04-30-2014, 12:03 AM   #33
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Quote:
Originally Posted by bcbowers View Post
Here's a decent explanation of an "Exhaust Brake":

HowStuffWorks "Exhaust Brakes"

And yes, they DO develop back pressure in diesel engines.
Agreed, I think some misunderstood my comments.

Exhaust brakes create back pressure which slows the engine.

From Banks Power site

"Diesel engines control engine speed and power output by throttling the amount of fuel injected into the engine. A diesel has no air throttle. Because it has no air throttle, a diesel engine offers virtually no engine braking when the driver lifts off the accelerator pedal. There just isnít a pumping loss to retard engine speed as the piston descends on the intake stroke. Air is free to enter the cylinder, restricted only by the flow capacity of the air cleaner, turbocharger compressor, intercooler, intake manifold, cylinder head port and intake valve opening. This can be disconcerting to a driver that is used to the engine braking produced by a gasoline engine, and it can be downright unnerving to the driver of a heavily-loaded diesel pickup or motorhome on a downhill grade, especially if the vehicleís service brakes begin to overheat and fade. Thatís why exhaust brakes, such as the Banks Brake, have become so popular for such diesel vehicles."
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Old 04-30-2014, 04:47 PM   #34
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Ok, based on Algoma's knowledge of the optional 8.9L ISL motor in a 2003 Alpine, I only have the engine brake with 2 settings. Based on my experience so far, the low setting is almost useless.

I actually had the coach out today and manually downshifted into 3rd gear when RPMs were low enough and it continued to slow down the coach and I could even go to 2nd as I continued to brake. So now I know I can downshift to allow the engine brake to continue to assist slowing.

For those that have both JAKE and PAC brake or have experience with both, Is the PAC brake more effective? Is the PAC brake something that can be added. I pull a trailer and welcome any additional braking.

Thanks everyone for the feedback and knowledge!
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Old 04-30-2014, 05:17 PM   #35
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Steve, the head mounted "engine compression brake" is a lot more effective that the "exhaust pac brake" , As far as adding more braking to your engine.......not sure, and I have never heard of Cummins engines doing this..., some of Mercedes diesels have both, compression and exhaust, they are the only one I have seen this set up on. On low the exhaust brake is activated, and on high , the compression brake and the exhaust both come on. On my semi, I had a 3 stage compression brake. So with the 2 stage I believe you are just using 2 of the heads(valves) and on stage one(low) you are using one head(valves) , on a 3 stage set up, on high all 3 heads(valves are used) due to slowing 80,000 lbs. The Coach manufactures of the lighter Coach's only put the 2 stage on them so as not to loose traction on the rear engine braking tires. I am not sure if any Coach manufacture installs a 3 stage compression brake? I am sure one could be added to your engine$$$$$$$ if needed, switch, new wiring, etc.
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Old 04-30-2014, 05:31 PM   #36
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Quote:
Originally Posted by JeepPuller View Post
Ok, based on Algoma's knowledge of the optional 8.9L ISL motor in a 2003 Alpine, I only have the engine brake with 2 settings. Based on my experience so far, the low setting is almost useless.

I actually had the coach out today and manually downshifted into 3rd gear when RPMs were low enough and it continued to slow down the coach and I could even go to 2nd as I continued to brake. So now I know I can downshift to allow the engine brake to continue to assist slowing.

For those that have both JAKE and PAC brake or have experience with both, Is the PAC brake more effective? Is the PAC brake something that can be added. I pull a trailer and welcome any additional braking.

Thanks everyone for the feedback and knowledge!

The engine compression brake, just like an exhaust brake needs rpms to be really effective. Your ISL will retard better with the rpms up around 2300-2400. You are doing exactly the right thing by downshifting further. You might consider having a Cummins shop change the default setting to 2nd or 3rd. The engine ECM and transmission TCU will work together to manage the shifts. Otherwise you can continue to downshift manually.


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Old 04-30-2014, 06:00 PM   #37
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Problem is - as the OP found out - if you are travelling at 65mph plus and lift your foot on a decent downhill run, almost NOTHING happens and in fact you are likely to go faster and faster. True, the valve closes and the transmission preselects to 2 or 4 or whatever, but it stays in 6th and the auxiliary brake just hasn't got enough force to control the speed.
Then the untrained driver applies the brakes just hard enough to keep the speed at 65 and pretty soon the brakes are red hot and "burning up"

What a trained driver would do is to brake quite heavily to get the speed down to the point where the transmission will drop down and the engine revs rise and the auxiliary brake does start doing something. Then he would monitor his speed and if it rose to target speed + 5% he would apply the brakes firmly to bring the speed down to target speed -5% and repeat as often as needed.
If the manual braking was needed too often then brake firmly until the transmission dropped one gear lower and then continue monitoring.

Regardless of whether the auxiliary braking system drops the transmission to a lower gear or the driver manually selects a lower gear, at 65 in 6th, the gearbox will not usually shift to a lower gear than 5th so manual brake application is nearly always needed to set things up in the first place.

Called "Snub braking" and there is heaps of information on the internet and it is the safe way to bring a heavy vehicle down a steep incline.
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Old 04-30-2014, 06:03 PM   #38
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Problem is - as the OP found out - if you are travelling at 65mph plus and lift your foot on a decent downhill run, almost NOTHING happens and in fact you are likely to go faster and faster. True, the valve closes and the transmission preselects to 2 or 4 or whatever, but it stays in 6th and the auxiliary brake just hasn't got enough force to control the speed.
Then the untrained driver applies the brakes just hard enough to keep the speed at 65 and pretty soon the brakes are red hot and "burning up"

What a trained driver would do is to brake quite heavily to get the speed down to the point where the transmission will drop down and the engine revs rise and the auxiliary brake does start doing something. Then he would monitor his speed and if it rose to target speed + 5% he would apply the brakes firmly to bring the speed down to target speed -5% and repeat as often as needed.
If the manual braking was needed too often then brake firmly until the transmission dropped one gear lower and then continue monitoring.

Called "Snub braking" and there is heaps of information on the internet and it is the safe way to bring a heavy vehicle down a steep incline.

Excellent post Tony. This is exactly how to use the service brakes to get down to a speed that the engine brake/transmission can control.


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Old 04-30-2014, 06:23 PM   #39
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I know we are in the " Motorcoach" world here, but as I read these posts, it makes me chuckle a bit......All the semi's cruising our country's network of highways have engine brakes on them........, make me wonder how all of these drivers make their "engine brakes effective"when they let off the throttle pedal(cruising at 1300 rpm's) and no automatic transmission to do the downshift for them and drive the rpm's of the engine up over 2300 rpm's..........to make the engine brake work?
OK , back to Motorcoaching........
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Old 04-30-2014, 06:37 PM   #40
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In West Virginia (and maybe other states) at the top of a steep hill there is a sign telling truckers to "engage low gear", so I take that as a clue that I should drop to 4 and control my speed to 55mph using the PAC brake and service brake in the "snub" braking mode (never knew it had a name!).
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Old 04-30-2014, 06:44 PM   #41
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I know we are in the " Motorcoach" world here, but as I read these posts, it makes me chuckle a bit......All the semi's cruising our country's network of highways have engine brakes on them........, make me wonder how all of these drivers make their "engine brakes effective"when they let off the throttle pedal(cruising at 1300 rpm's) and no automatic transmission to do the downshift for them and drive the rpm's of the engine up over 2300 rpm's..........to make the engine brake work?
OK , back to Motorcoaching........

They are just like us. Their Jake is on all the time. If they back out of the throttle in a relatively high gear and 1300 rpm, you'll hear the Jake sound off but they will only get mild slowing on level ground and none on a grade. They know exactly how to get the most performance out of their Jake and just like us, they do it with rpms.


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Old 04-30-2014, 06:57 PM   #42
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They are not like us!

Quote:
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They are just like us. Their Jake is on all the time. If they back out of the throttle in a relatively high gear and 1300 rpm, you'll hear the Jake sound off but they will only get mild slowing on level ground and none on a grade. They know exactly how to get the most performance out of their Jake and just like us, they do it with rpms.


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I disagree Steve, they are not like us........I did not and they do not have their engine rpm's anywhere close to where the diesels in Motorcoach's w/Allison transmission" programed to downshift and shove the rpm's up over 2300-2500 rpm's. Most all truck drivers are lucky if their engine is at 2000 rpm's when descending a steep hill, and using their service brakes also, if one pays attention and listens, semi's engine's are not turning the rpm's as these automatic rv's are when using the engine brakes.......
I have logged over 1,000,000 miles in my driving career and know how a engine brake works and what stage to use(3 stage) in different grade conditions.......As most know, my Allison does not downshift on its own when I let off the throttle pedal..........it stays in 6th, and I am in control from there..........
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