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Old 01-10-2013, 06:18 PM   #1
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Engine brake (Jake) question

I am accustomed to a PacBrake and the feel of engagement. When I press on the PB activation switch, I get immediate results under most conditions. My new-to-me coach has a Jake brake. It seems to be difficult to engage under normal slowing down to stop conditions. When it finally kicks in, the braking is good but it almost feels like the switch is not making contact much of the time. No tranny downshift and certainly no engine braking. I have not disassembled the foot switch to see if there is a repair that can be done there. Seems like the first place to start. Anyone had similar engine brake malfunctions??

Ron
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Old 01-11-2013, 06:49 AM   #2
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ron is there a switch for strength control on the dash, showing 1,2,3, or 1,2? what engine in your motor home?
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Old 01-11-2013, 07:59 AM   #3
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Quote:
Originally Posted by RonNBama View Post
My new-to-me coach has a Jake brake. It seems to be difficult to engage under normal slowing down to stop conditions. When it finally kicks in, the braking is good but it almost feels like the switch is not making contact much of the time. No tranny downshift and certainly no engine braking. I have not disassembled the foot switch to see if there is a repair that can be done there. Seems like the first place to start. Anyone had similar engine brake malfunctions??

Ron
These folks sell a foot switch www.rvchassisparts.com , click "chassis electrical system".

And here's a trouble shooting link http://www.jacobsvehiclesystems.com/...ting-Guide.pdf
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Old 01-11-2013, 05:14 PM   #4
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Yep, switch on the console for Hi/Lo. Position of switch does not seem to have any affect on the engagement. Thanks for the links, I will do my research.

Cummins ISM 500 engine.

Whew! Looking through that troubleshooting manual is an eye opener. Many more "moving parts" than I suspected. I do suspect a grounding problem based on brief scanning of some of the trouble points. Already had some loss-of-ground problems in another system.
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Old 01-11-2013, 08:55 PM   #5
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Originally Posted by RonNBama View Post
I am accustomed to a PacBrake and the feel of engagement. When I press on the PB activation switch, I get immediate results under most conditions. My new-to-me coach has a Jake brake. It seems to be difficult to engage under normal slowing down to stop conditions. When it finally kicks in, the braking is good but it almost feels like the switch is not making contact much of the time. No tranny downshift and certainly no engine braking. I have not disassembled the foot switch to see if there is a repair that can be done there. Seems like the first place to start. Anyone had similar engine brake malfunctions??

Ron

Could also be a computer parameter. Some can be set up in many different modes. You may have to have someone plug into your system to change the parameter. Personally I like my Compression brake to come on full power when I release the throttle. If it is not a parameter issue, you may have problems with the wiring. Could also be in the switch or in the jake head itself. Hopefully it is not in the jake head. If you find that it is the jake head you will most likely have to take it to a certified Jake Brake mechanic. They will have to pull your valve covers off to fix the problem. If you have to go this route you should probably consider replacing the Jake solenoids and doing a tune up on the engine. Your already there. Not that much more to get this done. A tune up would consist of valve adjustment, injector adjustment and jake adjustment. Good luck. Curious to find out what you find out.


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Old 01-11-2013, 09:03 PM   #6
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Could also be a computer parameter. Some can be set up in many different modes. You may have to have someone plug into your system to change the parameter. Personally I like my Compression brake to come on full power when I release the throttle. If it is not a parameter issue, you may have problems with the wiring. Could also be in the switch or in the jake head itself. Hopefully it is not in the jake head. If you find that it is the jake head you will most likely have to take it to a certified Jake Brake mechanic. They will have to pull your valve covers off to fix the problem. If you have to go this route you should probably consider replacing the Jake solenoids and doing a tune up on the engine. Your already there. Not that much more to get this done. A tune up would consist of valve adjustment, injector adjustment and jake adjustment. Good luck. Curious to find out what you find out.


Bruce

After reviewing what you wrote. I would also check the throttle. If it is not fully disengaging when you let you foot off the throttle, that could also be your problem. Check for dirt or foreign objects that would block your throttle from going to idle. I just had that problem today with a semi truck that we own. A foreign object had stuck in the throttle mechanism causing slow response to the idle position, thus jake was not working properly. Hope this helps.
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Old 01-12-2013, 08:44 AM   #7
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Good tips, thanks. Never considered the throttle position as a factor (shows just how much I don't know about this system). The engagement is "erratic". Sometimes it works perfectly and then at the next slow-down it does not engage. I have tried pressing very hard, softly, at an angle, etc etc. Now that I know I am interfacing with a half dozen electronic sensors and parameters I will hope for the best with each press.
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Old 01-19-2013, 01:15 PM   #8
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If the transmission is Allison the automatic downshift parameters may have been disabled (you have to downshift manually) to achieve maximum holdback.
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Old 01-19-2013, 07:19 PM   #9
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Jakes are most effective at higher rpms, if you are geared up and engine speed is low, there is very little brake hp generated.
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Old 01-19-2013, 09:17 PM   #10
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Try some Lucas upper cylinder lubricant aditive. It made mine more responsive.
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Old 01-20-2013, 11:44 AM   #11
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The Jake Brake engages only when you let off the accelerator fully - merely slowing won't do it. If you are still in 5th or 6th gear (higher speed & low RPMs, you won't feel much, if any, retarding. However the tranny shifter should show that the target gear has changed to either 4th or 2nd, depending on how it is programmed, and retarding will increase as downshifting occurs. The Allison won't downshift until speed drops enough to prevent over-reving, though. You may have to help it a bit with the service brakes to allow it to downshift. On most coaches it also won't engage if the Cruise is on & active, thus enabling the Cruise to coast when appropriate. A touch of the brake pedal disengages the cruise and allows the Jake to go to work.

The High/Lo switch engages the Jake on all cylinders or only half of them (50% braking). On mine, the Lo position is actually the 100% position and High the 50%. Seems backwards to me, but that's how mine is wired. Yours may be different - it's up to the installer.
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Old 01-20-2013, 02:48 PM   #12
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Drove the coach today and the Jake functioned perfectly. I dunno, I may have been resting my foot on the accelerator pedal or something really dumb like that. I know the Hi/Lo switch is functional as I can feel/hear a difference between the toggle-forward, toggle-rearward position. Might give that upper cylinder lube a try. The Cummins rep at a seminar I attended awhile back seemed to think the Lucas products were as good as any on the market, so I will add a dose at the next oil change (which is now).

Thanks for the thoughts and suggestions.
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