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2000 e7 427 jake issues


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I've got a 2000 cx613 vision with an e7 427 at my shop. After years of the Jakes not working we finally solved the problem. It turned out it was the switch on the clutch pedal. Now the issue we have is the jakes dont come on till the engine gets to about 1300 rpm when slowing down and down shifting. This seems a little low to me as when down shifting I go to the next lower gear at 1200 rpm. Has anyone else had this problem and how did you fix it? Is this just the Jakes being out of adjustment, a computer issue or a combination of the two? 

Edited by mackrmodel686st
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My '95 does something similar, won't work above ~1500 r if the engine is hot unless I've been using it a lot before the engine is up to temperature. Guys here will likely point you in the direction of low oil pressure at the cylinder heads due to worn camshaft bearings? Supposedly there's an external oil gallery routing that can be done to compensate but I havent read a good write up on it to understand what exactly it's for/fixes.

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This is a master sheet for updates and issues, make note of the columns with service bullletins. Those bulletins can be downloaded on Mack E-media, they will give better details about issues or product improvements. The bottom of page 2 addresses the drop out and external supply kit repair Joe is referring to. 

sb266017.pdf

Edited by Mack Technician
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My 2001 had the problem the dealer was putting oversize bearings but after several trucks they came up with a fix a external oil line or higher volume /  pressure pump I ended up with the pump .

Ed

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If your saying if your at 1800rpms and activate the jake that it wont come on til the rpms drop to 1300.?   If so sounds like in the computer.  It should come on at any rpm above 8 or 900 rpm.   I have the same set up and mine does.  The oil lines and pump just make the Jake work harder. Has nothing to do about when it comes on.

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A typical drop-out occurs in lower RPM scale. Usually as you hit around 1,000-1,200 it would get weak and fade. I debated after reading the complaint....possibly...if things get really sloppy....could you lose oil in the upper range too when you also need higher volume for high demand then get Jake brakes in a short window, a “sweet spot”, where consumption and supply align for a moment? Agree with Wilbur, but I don’t dismiss the possibilities.

a very quick check would be to run a little break-in wire to the cab or monitor the Jake relay while driving. 

Edited by Mack Technician
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His issue could simply wear and just not enough volume of oil!  huge delay for oil pressure to build as well the jake heads could be worn to the point there is to much oil passing the slaves! My question is How long of a grade are you on with the brake on and engauged ? I would run a temp  TEST wire with a light to ground on the jake wires on the head to identify if indeed the Solenoid is being powered while the engine is at high  RPMS this will put to bed an ECU issue as Wilbur is suggesting  and then you can focus your efforts on the mechanical aspect of this if need be! This issue is most commonly A physical Volume issue !

Just Sayin!  😡

 

 

 

 

 

 

Edited by fjh
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  • 2 weeks later...

My 2001 CH tractor, with a 427 motor- jake will cut out at about 1550 rpm and come back on around 1000 ~ 1100 and stay on till 8, 900.

Has all the “upgrades”...

I got tired of an intermittent jake and wired it direct off a toggle switch.  Jake works perfect. I’m thinking mine must be computer and or electrical.  

Truck has 1.2 million miles. Almost 40000 hours. Only rebuilt once at 600k.   

 

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3 hours ago, masterwelder said:

My 2001 CH tractor, with a 427 motor- jake will cut out at about 1550 rpm and come back on around 1000 ~ 1100 and stay on till 8, 900.

Has all the “upgrades”...

I got tired of an intermittent jake and wired it direct off a toggle switch.  Jake works perfect. I’m thinking mine must be computer and or electrical.  

Truck has 1.2 million miles. Almost 40000 hours. Only rebuilt once at 600k.   

 

You wired right from the head to a switch bypassing the relays and clutch switch and dash switch.?  I did that for a test once ,but didnt leave it that way. The way you have it you can engage the jake with the throttle depressed and make a lot of smoke.

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If you're the owner operator, it's no big deal. Just don't let anyone else drive it. Great to hear you have 40,000 hours on yours! My 95 e7-350 has 19,550+; curious how many hours I'll get out of it til it gets rebuilt. Runs like a champ!

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