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01-10-2013, 05:18 PM
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#1
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Retired Senior Member
Join Date: Oct 2006
Posts: 1,093
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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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01-11-2013, 05:49 AM
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#2
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Junior Member
Join Date: Jun 2011
Posts: 9
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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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01-11-2013, 06:59 AM
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#3
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Senior Member
Join Date: Dec 2009
Location: TX
Posts: 725
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Quote:
Originally Posted by RonNBama
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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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
__________________
96 Prevost Liberty XL40'-Past MHs: 02 Monaco45'Sig,00Monaco43'Sig,99Monaco42'Exec,98Mona co42'Sig,98Newmar38'DSDP(pictured),88FW26'Jamboree .
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01-11-2013, 04:14 PM
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#4
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Retired Senior Member
Join Date: Oct 2006
Posts: 1,093
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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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01-11-2013, 07:55 PM
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#5
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Junior Member
Join Date: Dec 2012
Posts: 26
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Quote:
Originally Posted by RonNBama
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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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
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01-11-2013, 08:03 PM
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#6
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Junior Member
Join Date: Dec 2012
Posts: 26
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Quote:
Originally Posted by bginpa
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
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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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01-12-2013, 07:44 AM
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#7
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Retired Senior Member
Join Date: Oct 2006
Posts: 1,093
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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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01-19-2013, 12:15 PM
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#8
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Member
Winnebago Owners Club
Join Date: Jan 2011
Posts: 41
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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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01-19-2013, 06:19 PM
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#9
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Senior Member
Join Date: Jan 2012
Location: Chetwynd, BC
Posts: 293
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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.
__________________
Brentw
3500 Duramax dually
Fuzion 325 Toy Hauler with a GL1800 Goldwing
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01-19-2013, 08:17 PM
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#10
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Senior Member
Workhorse Chassis Owner Triple E Owners Club
Join Date: Nov 2004
Location: Williams Lake,BC Canada
Posts: 1,230
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Try some Lucas upper cylinder lubricant aditive. It made mine more responsive.
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2020 Triple E Wonder RTB
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01-20-2013, 10:44 AM
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#11
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Moderator Emeritus
Join Date: Jan 2000
Location: West Palm Beach, FL. USA
Posts: 27,713
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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.
__________________
Gary Brinck
Former owner of 2004 American Tradition and several other RVs
Home is West Palm Beach, FL
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01-20-2013, 01:48 PM
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#12
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Retired Senior Member
Join Date: Oct 2006
Posts: 1,093
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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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