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Old 06-02-2011, 07:25 PM   #1
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Jake Brake Question...???

Good Evening,

Hubby wanted me to ask a question about what he thinks is a jake brake question.... Last weekend on the way to the campground, the coach handled as it usually does but on the way home, he felt it handling differently. He thinks that he may have engaged a jake brake somehow. He says that when he lets up on the gas and the coach naturally slows down, it feels as though the coach is down-shifting without his intervention. He has no idea what he might have done or how to remedy it. We cannot find any manual for the transmission or similar.

Any ideas??? Is there a switch or button that he may have inadvertantly engaged?? We have a 400 HP Caterpillar with an Allison 6 speed transmission. (And if it is important, we have a 2005 Fleetwood Revolution LE, but hopefully other coach owners may have the same engine and transmission and be able to offer suggestions...)

Faith and Bob
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Old 06-02-2011, 07:34 PM   #2
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Sounds like normal operation for an jacobs exhaust brake or traditional jacobs engine brake ...the engine brake would be louder and more noticeable. My coach has a switch on the dash labeled "Exhaust Brake." I have it on whenever driving in traffic, and use it on the highway to keep from gaining too much speed on downgrades.
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Old 06-02-2011, 07:39 PM   #3
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Lets make sure we are talking apples and apples here. When you say Jake Brake are you talking about an engine compression brake or an exhaust brake? Engine compression brakes on MHs normally have a foot switch and a hi and low switch and an exhaust brake has a switch to turn it on and it is automatically activated when you let up on the accelarator. If you have a exhaust barke and the switch is left on then it will do what you are talking about. Both the engine compression brake and the exhaust brake when activated will result in the transmission having a aggressive downshift schedule.

The exhaust brake made by Jacobs is NOT a Jake brake but a Jacobs exhaust brake. A Jake brake is a engine compression brake. I am not sure that a CAT C9 400hp ever had a Jake brake.
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Old 06-02-2011, 07:59 PM   #4
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Thanks for the replies so far. I have read them to hubby and he admits that he may be calling it a "Jake Brake" and it may be simply an Jacobs exhaust brake. He said that there is a switch on the left hand side of the drivers space that reads exhaust brake or something similar, but he is not sure what position is off and what position indicates that it is on or engaged.

But what Mike described is exactly what the coach is now doing as we drive and the downshifting is quite noticable and "aggressive" is an excellent description. I felt it quite strongly coming home last weekend and commented on what felt so weird with his driving...

Is this something that should be used all the time and should we just get used to the way it feels??

Faith and Bob
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Old 06-02-2011, 08:26 PM   #5
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You probably have a "pac brake" which is an exhaust brake and has nothing to do with engine head exhaust valves. A true "jake" brake will have a selection for hi/lo or similar. This dictates whether the engine uses 3 or 6 cylinders when activated.
AFChap is correct in that a jake (or engine) brake is louder and more noticeable.
The down shifting is normal and I dislike it as I believe 2500 rpms or higher is too high for a Cat........just my opinion. While I do use it I will turn it off and on as needed as mine is programed to activate with deceleration.
If you have a rocker switch that activates the brake the side of the switch with the "slash" mark, when depressed will activate it.
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Old 06-02-2011, 08:26 PM   #6
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Faith take the MH out and try both positions of that switch. Most likely the position it is in now is on. Try both positions so you know what is on or off. It doesn't hurt to drive on flat open road with it on other than it gets a little aggressive and bothersome. It is really designed to give you braking force from the engine exhaust when going down hills so you don't have to use the footbrake and wear out the brakes or overheat them on steep grades. You will find it very useful in the mountains.

Just as a point of interest I can hardly hear my real Jake Brake from the drivers seat. One of these days I want to follow it while my DW drives and have her activate it and see how loud it really is.
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Old 06-02-2011, 08:58 PM   #7
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You probably have a "rocker switch" labeled hi and lo where when you press down on one side or the other the brake is enabled. If the switch is in the middle with neither side pressed down it is off. This is the way mine operates.

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Old 06-02-2011, 09:22 PM   #8
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A quick check which hasn't been mentioned yet is to look at your Allison shifter display when taking your foot off of the accellerator. Unless I'm really missing something, the "requested gear" display will immediately change from 6 (for example) to 2 (if programmed such). It does sound exactly like how my rig operates with what I think is an engine compression brake (?) with "Lo" engaging 3 cyclinders ...etc.

Best of luck...

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Old 06-02-2011, 09:40 PM   #9
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Rick, exhaust brakes also engage an aggressive downshift schedule in the Allison. I don't believe the CAT C9 has a compression brake
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Old 06-03-2011, 12:43 AM   #10
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Got it Mike, but isn't the OP's question whether or not some sort (any sort)of engine brake is engaging causing the agressive downshift... as opposed to some sort of transmission malfunction causing the behavior he's seeing? I was just thinking the Allison display would give valuable data if it indicated an immediate demand for the downshift when he backed off the accellerator.


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Old 06-03-2011, 06:31 AM   #11
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Quote:
Originally Posted by fansill View Post
Is this something that should be used all the time and should we just get used to the way it feels??

Faith and Bob
Do not use in rainy or anytime the road is "slick" weather.

Another comment. You don't say what chassis your mh is on. If its on a Freightliner Custom Chassis, call 1-800-FTL-HELP with the last 6 numbers of you VIN and they can tell you what kind of engine braking system you have.
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Old 06-03-2011, 06:38 AM   #12
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Thank You!!!

You Guys are Great!!! You always come through for me and I don't know what I would do without your help...

Faith

Now off to Maine we go.....
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Old 06-03-2011, 12:55 PM   #13
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The 2005 Rev LE is on a Fleetwood Liberty Chassis which can use either Spartan or Freightliner components at the front and rear. Most are Spartan-based.

Cat does offer an engine compression brake in the C9, but it's not a Jacobs. Not sure if it was available in 2005, though.

Faith: Where in Maine are you headed? We will be at the Narrows Too near Bar Harbor 6/15/-7/31.
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Old 06-03-2011, 03:21 PM   #14
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It can be a Jacobs exhaust brake. Jacobs makes them.
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