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Old 04-22-2014, 09:52 AM   #1
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Exhaust brake

Can the exhaust brake be applied at any speed?
I was told by the original owner not to use the exaust brake above 55 mph.
I burned up my brakes using the peddle to much above 55.
I could not get it slowed down. First time in 3 years and 25k miles I’ve had a problem. An expensive problem.
My partner with an American Dream says it’s OK to use at any speed.
You can’t hurt it. Is that correct?
Thanks, Gator, 2000 with 350 hp>
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Old 04-22-2014, 09:58 AM   #2
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Simply put, yes you can use it at any speed, the Allison TCM(Transmission control module) and the engine ECM(Engine control module) work together to not allow you to over rev the engine, or hurt the transmission. Mine is on all the time and I use it all the time.
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Old 04-22-2014, 10:04 AM   #3
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Prior owner was misinformed
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Old 04-22-2014, 10:16 AM   #4
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Yes! After putting 430K on a CAT E model, it never did any harm turning it on for mountains or slowing down, would hold 80,000 lb at 70 MPH down I 515 in Las Vegas without touching the brakes and thats a pretty good slope. Have had it on the entire length of the old La Veta Pass in Co which takes about 45 min to descend from 99500 to 6000 ft and was twisty windy 2 lane that went through downtown La Veta It is meant to be used. Turn it on. 1961: The Jacobs Engine Brake | Overdrive Retro
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Old 04-22-2014, 10:45 AM   #5
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The prior owner was wrong. You can turn the engine brake on at any speed. I selectively activate it rather then leave it on all the time. First my cruise control will not engage with the engine brake on. Plus I don't want the brake slowing me down whenever I'm just coasting. That is a pain, and not fuel efficient.
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Old 04-22-2014, 06:15 PM   #6
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I leave mine on and use a light touch on the accelerator pedal to keep the exhaust brake from actuating if I want to coast.
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Old 04-22-2014, 08:38 PM   #7
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Depends! Firstly, anyone with an ISL engine does not have an exhaust brake, that engine has an engine brake. But in your case with an ISC you do have an exhaust (or PAC) brake. When it was shipped from the factory the transmission was programmed so that when you turn on the exhaust brake the transmission would attempt to select 4, but it will only do that when the engine revs are low enough not to over rev the engine. In my experience this is around 55 mph. So back to your original question both statements are sort of correct. You can switch on the exhaust brake at any speed, but it will not do anything until the speed drops to 55 mph.
Now some people have had the Allison reprogrammed so that it does not pre-select 4 but will operate the exhaust brake in any gear. I tried this and it has very little effect in 5 and 6 as these are overdrive gears. There is no harm in doing this, it just means that you have to manually move down through the gears. Truth is that the exhaust brake is not as effective as the engine brake so you will still have to use the service brakes. Getting in to a low gear and keeping the revs high gets the most out of the exhaust brake.
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Old 04-22-2014, 08:40 PM   #8
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Old 04-22-2014, 09:04 PM   #9
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Not really true.....

Quote:
Originally Posted by Algoma View Post
Depends! Firstly, anyone with an ISL engine does not have an exhaust brake, that engine has an engine brake. But in your case with an ISC you do have an exhaust (or PAC) brake. When it was shipped from the factory the transmission was programmed so that when you turn on the exhaust brake the transmission would attempt to select 4, but it will only do that when the engine revs are low enough not to over rev the engine. In my experience this is around 55 mph. So back to your original question both statements are sort of correct. You can switch on the exhaust brake at any speed, but it will not do anything until the speed drops to 55 mph.
Now some people have had the Allison reprogrammed so that it does not pre-select 4 but will operate the exhaust brake in any gear. I tried this and it has very little effect in 5 and 6 as these are overdrive gears. There is no harm in doing this, it just means that you have to manually move down through the gears. Truth is that the exhaust brake is not as effective as the engine brake so you will still have to use the service brakes. Getting in to a low gear and keeping the revs high gets the most out of the exhaust brake.
I have read on here John and I was corrected before, Some of the Early models of the ISL came with a exhaust brake, so.......it could be true
https://quickserve.cummins.com/info/..._nondodge.html
http://www.irv2.com/forums/f258/engi...th-149533.html

Why does it not come on till 55 mph? A exhaust brake should come on even at 70 mph and not downshift till around 60-62 mph to the preset gear, or maybe 5th.......It should downshift when the rpm's and speed are correct for the shift, but just because it did not downshift due to speed or rpm's does not mean that the exhaust brake is not on or working correctly. Maybe what you are describing is a Alpine thing? Maybe the way they set their Coach's up?
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Old 04-23-2014, 10:50 AM   #10
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It may be that some ISL engines had the E-brake fitted instead of the C-brake as you point out, but I have not heard of these being on Alpine coaches. I could be wrong though.
The exhaust brake is controlled by the transmission ECU and the on-off switch is merely a request to activate the brake. In experiments I did the brake did not activate until the transmission shifted down to 4. Flicking the switch on at 70mph in 6 did not activate the brake. As I said above, if yours is not programmed to pre-select a lower gear the exhaust brake will activate at any speed providing you have taken your foot off the accelerator. The programming of the ECU including what the economy button does is specific to the coach, so maybe Alpines are different.
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Old 04-23-2014, 11:32 AM   #11
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I'm surprised that in exhaust brake mode that it pre-selects 4th gear. All the units I have experienced were programmed to pre-select 2nd gear when the exhaust brake activates. The brake should activate at any speed, and the transmission will downshift accordingly until it drops down into 2nd gear.

I think there are some advantages to the 4th gear pre-select, but I think the 2nd gear pre-select is more "automatic" in that the operator doesn't have to downshift manually when the RPMs drop as you slow down.

The braking force of an exhaust brake or an engine brake is greatly affected by the engine RPMs. Higher RPMs equates to higher braking horsepower, and engine brakes are able to generate considerably more brake HP than the same engine with an exhaust brake.
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Old 04-23-2014, 11:54 AM   #12
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Thanks for all the information and the great advice.
I drove about 1000 miles home from Moab Easter Jeep Safari with cracked rotors which ground down the pads. Stopped OK but not great. I used the Pac brake almost all the time and at any speed as I will in the future. I bought the front end parts in Richfield Utah , just encase I couldn’t make it home. Very stressful drive but a great jeep trip.
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Old 04-25-2014, 05:08 PM   #13
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Quote:
Originally Posted by gatorv View Post
Thanks for all the information and the great advice.
I drove about 1000 miles home from Moab Easter Jeep Safari with cracked rotors which ground down the pads. Stopped OK but not great. I used the Pac brake almost all the time and at any speed as I will in the future. I bought the front end parts in Richfield Utah , just encase I couldn’t make it home. Very stressful drive but a great jeep trip.
Sorry to hear of your issues. I think your questions have been answered. Personally, I pretty much never turn my Pac Brake off; the exception would be in significant traffic where it shifts a lot from 6th to 4th.

Were you in Canyonlands RV Park during EJS? I think there were four Alpine's.
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Old 04-25-2014, 05:22 PM   #14
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Quote:
Originally Posted by Algoma View Post
Depends! Firstly, anyone with an ISL engine does not have an exhaust brake, that engine has an engine brake. But in your case with an ISC you do have an exhaust (or PAC) brake. When it was shipped from the factory the transmission was programmed so that when you turn on the exhaust brake the transmission would attempt to select 4, but it will only do that when the engine revs are low enough not to over rev the engine. In my experience this is around 55 mph. So back to your original question both statements are sort of correct. You can switch on the exhaust brake at any speed, but it will not do anything until the speed drops to 55 mph.
Now some people have had the Allison reprogrammed so that it does not pre-select 4 but will operate the exhaust brake in any gear. I tried this and it has very little effect in 5 and 6 as these are overdrive gears. There is no harm in doing this, it just means that you have to manually move down through the gears. Truth is that the exhaust brake is not as effective as the engine brake so you will still have to use the service brakes. Getting in to a low gear and keeping the revs high gets the most out of the exhaust brake.
Not exactly correct regarding it won't do anything until the speed drops to 55 mph.

The exhaust brake will engage immediately; the transmission pre-selects a pre-programmed gear and starts to downshift to this gear selected, but the Allison is smart enough to not downshift until the coach is at a safe RPM so as to not damage the transmission or engine.

The engine braking is most effective at higher RPM's, so you may not feel the effect of the exhaust brake until it does downshift.

Mine was pre-programmed from the factory to downshift to '2', which I found too aggressive, so I had it re-programmed to downshift to '4'. I can always manually downshift to '3' or '2' if needed.
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