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Old 09-18-2018, 11:42 AM   #1
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Jake vs Exhaust Brake question on operation

My former DS had a Cummins with a Jake (eng compression) brake. The coach I am looking at now has an exhaust brake (Cat C9). When test driving, naturally I wanted to check the exhaust brake coming off the freeway and stopping at the bottom of the ramp. The owner said "please turn off the exh brake as you are only supposed to turn that on when going down a hill or mountain." Is he right, or should I call BS on that?


BTW, at the turn from the off ramp, the coach died. Low voltage. He learned the hard way that you do not let the fuel tank get below 1/4 mark as he could not start the genny. He called his wife to bring two 5-gal containers of diesel. Needless to say, mamma was not happy. He got the engine started after getting the genny to run. He just called me. Replacing the alternator.
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Old 09-18-2018, 11:49 AM   #2
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[Moderator edit]

Exhaust brake should be able to be ON all the time and fully CLOSED w/o any ill affects.
Excessive back pressure is controlled via a bypass butterfly OR via a metered orifice

(excessive back pressure can damage valve train but designs of exhaust brake take that into account)


When you let off accelerator the exhaust brake should close
When you press on accelerator the exhaust brake should open


Down hill/up hill/stop and go traffic/full interstate speed....shouldn't matter.
Turn it on and use it when you want
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Old 09-18-2018, 11:52 AM   #3
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The only time I turn my exhaust brake off is on level highways when using cruise control , because if you get to a rolling section of highway and the cruise control goes to zero throttle to coast the exhaust brake engages .

JMHO: The owner is passing on misinformation , if you do purchase the coach , how/when, you use the exhaust brake is your option.
The more it's used the less likely it is to rust up .
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Old 09-18-2018, 11:53 AM   #4
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I've owned both a Pac brake and a Jacobs brake. Other than the Hi/Low adjustability of the Jacobs brake I used them the same.
On some you do have to turn off the engine brake for the cruise to work.
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Old 09-18-2018, 12:15 PM   #5
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Based on posts here, I should add that I was not using the cruise control.
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Old 09-18-2018, 01:56 PM   #6
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Don't know about the smaller engines, but both my two 3406Es and a C-15 I drove some where programmed if the Jake was on and the cruise set Jake would not come on until a few MPH over the set speed. If both cruise and Jake on, but speed not set, the Jake did not come on until I touched a brake. If the cruise was off, Jake at closed throttle...
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Old 09-18-2018, 02:15 PM   #7
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Quote:
Originally Posted by Skip426 View Post
The only time I turn my exhaust brake off is on level highways when using cruise control , because if you get to a rolling section of highway and the cruise control goes to zero throttle to coast the exhaust brake engages .

JMHO: The owner is passing on misinformation , if you do purchase the coach , how/when, you use the exhaust brake is your option.
The more it's used the less likely it is to rust up .
Well Skip,
Not on all coaches. On our coach, an '04 Itasca Horizon 36GD with the CAT C-7 330HP, and two friends coaches, One, an '05 36G Meridian with the C-7 350HP and another, an '06 36G Journey with the CAT C-7 350HP, if the cruise is set to a given speed, and you start a downhill stretch, and the cruise goes to a "zero throttle", all three coaches simply pick up speed and, there is no Exhaust brake application.
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Old 09-18-2018, 02:33 PM   #8
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"Sandy Swede".....I would be concerned about the owner's statement about using the exhaust brake on off ramps. Is it possible he was having this stalling issue with it and didn't want you to see it happen.

Pretty basic facts....exhaust brake good, engine brake better. Both the Caterpillar and even more, the Cummins can have their computers tweaked to operate in many different ways with an engine brake and exhaust brake. You can change, them to engage the brake with your foot off of the throttle or only when you tap the brake. You can change what gear they shift to. There are just too many variables from coach to coach. Learn how yours works and change it if you don't like it.
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Old 09-18-2018, 02:47 PM   #9
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Quote:
Originally Posted by Old-Biscuit View Post
[Moderator edit]


Exhaust brake should be able to be ON all the time and fully CLOSED w/o any ill affects.
Excessive back pressure is controlled via a bypass butterfly OR via a metered orifice

(excessive back pressure can damage valve train but designs of exhaust brake take that into account)


When you let off accelerator the exhaust brake should close
When you press on accelerator the exhaust brake should open


Down hill/up hill/stop and go traffic/full interstate speed....shouldn't matter.
Turn it on and use it when you want
I second this....however I also add that the exhaust brake on mine does engage when cruise is on and I go down a slight hills, so I turn it off on long flat(or nearly flat) highways
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Old 09-18-2018, 03:06 PM   #10
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Our last motorhome had an exhaust brake with a C7 our new one has an ISX with a 3 stage Jacob's.

As far as use the exhaust brake is softer its comes on a bit smoother and helps slow.

The engine brake on stage one comes on a bit more abruptly and slows the coach a bit more. On stage two I have pulled off the highway to a rest area and without touching the brake I slow down to 25 quickly. Stage 3 I never use. If I was in a situation where it was an emergency stop I would hit stage 3.

As far as the guy not wanting you to use it on the off ramp in some parts of the country I have seen signs banning engine brakes on off ramps, this I presume it's due to the noise. The exhaust brake makes no noise and neither does a muffled engine brake.
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Old 09-18-2018, 07:55 PM   #11
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Quote:
Originally Posted by Mark D View Post
Our last motorhome had an exhaust brake with a C7 our new one has an ISX with a 3 stage Jacob's.

As far as use the exhaust brake is softer its comes on a bit smoother and helps slow.

The engine brake on stage one comes on a bit more abruptly and slows the coach a bit more. On stage two I have pulled off the highway to a rest area and without touching the brake I slow down to 25 quickly. Stage 3 I never use. If I was in a situation where it was an emergency stop I would hit stage 3.

As far as the guy not wanting you to use it on the off ramp in some parts of the country I have seen signs banning engine brakes on off ramps, this I presume it's due to the noise. The exhaust brake makes no noise and neither does a muffled engine brake.

Thanks, Mark.
He was not concerned about the noise, he thought that the exhaust brake should be used only if you are going down a hill or mountain.
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Old 09-18-2018, 08:04 PM   #12
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Quote:
Originally Posted by Sandy Swede View Post
Thanks, Mark.
He was not concerned about the noise, he thought that the exhaust brake should be used only if you are going down a hill or mountain.
He's wrong. I use the engine brake on my ISX whenever I want to, off ramps, in town, out of town even in the rain just not on Med or High!
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Old 09-18-2018, 08:11 PM   #13
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Quote:
Originally Posted by FIRE UP View Post
Well Skip,
Not on all coaches. On our coach, an '04 Itasca Horizon 36GD with the CAT C-7 330HP, and two friends coaches, One, an '05 36G Meridian with the C-7 350HP and another, an '06 36G Journey with the CAT C-7 350HP, if the cruise is set to a given speed, and you start a downhill stretch, and the cruise goes to a "zero throttle", all three coaches simply pick up speed and, there is no Exhaust brake application.
Scott
Ditto with my 06 Ccat C7 350hp -- cruise goes to zero throttle and the exhaust brake just watches asw we pick up speed.

BTW OP, one should use the exhaust brake alot, underuse is the #2 reason for the valve to stick open. #1 reason, no exhaust brake maintenance. Ask the seller if he has any exhaust brake oil left over. If he looks at you like you're speaking swahele, he has never serviced his exhaust brake and it likely doesn't work. $$$$$
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Old 09-18-2018, 10:00 PM   #14
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I leave mine on all the time........I may turn it off if I want to coast.... like in heavy slow stop n go traffic or if driving slow thru a small town.
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