CM870 Jake problem
02-11-2019, (Subject: CM870 Jake problem ) 
Post: #1
CM870 Jake problem
Hello guys! I have Cummins CM870 with 1.238xxx miles and my engine brakes works weird. I did change 2 solenoids and also new wires that runs under head cover, tune up is done too, I did it all last summer and nothing helped. I noticed that when engine is cold, under 180F Jake brake works as it should but after it reaches 180F its become weak and shakes whole truck when is on. But sometimes when I go down the hill I turn Jake's on and at beginning it shakes and after a while something may kicks in and jakes works fine...when Jake's are weak I'm getting only like 3-5psi of boost, but when Jakes strong with 16RPM boost goes up to15-18PSI. Thank you for your help.
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02-11-2019, (Subject: CM870 Jake problem ) 
Post: #2
RE: CM870 Jake problem
I notice when i have a vibration in my jakes it is becaise 1 stage isn't actuating. You have changed the harness and solenoids but have you inspected the rockers? They most likely need to be replaced with that many miles. The piston inside could be worn and sticking or leaking too much oil around them at operating temp...i believe you can remove the piston by taking out the adjustment screw but i have never disassembled one that far.

Also the rocker shaft itself could have too much wear....
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 Thanks given by: DKenworth
02-11-2019, (Subject: CM870 Jake problem ) 
Post: #3
RE: CM870 Jake problem
I had an 870 back in 2005, they had a recall on the jakes, they were ventilating the blocks, I wish I could remember what was actually replaced in this recall. The symptoms you have, if my memory serves me right, are the same. Not to scare you, but I would get the truck fixed ASAP.
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 Thanks given by: Rawze , DKenworth
02-11-2019, (Subject: CM870 Jake problem ) 
Post: #4
RE: CM870 Jake problem
It could also be the turbo actuator control module. These things fail intermittently causing these exact symptoms. Are you experiencing intermittent low boost pressures while pulling? Could be an avenue to chase.The jakes are assisted with the VGTurbo closing. 3rd stage boost pressure should be any where from 18-32 psi depending on rpm and demand that the engine sense's. Higher rpm, steeper hill, heavy load, the higher the boost\backpressure will go. If it intermittently drops after repairing\replacing solenoids and harness and proper adjustment then I'd take a good hard look at the VG turbo air circuit and the control module especially. like I said this will normally be accompanied with intermittent low pulling boost.
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 Thanks given by: Rawze
02-12-2019, (Subject: CM870 Jake problem ) 
Post: #5
RE: CM870 Jake problem
(02-11-2019 )Chamberpains Wrote:  It could also be the turbo actuator control module. These things fail intermittently causing these exact symptoms. Are you experiencing intermittent low boost pressures while pulling? Could be an avenue to chase.The jakes are assisted with the VGTurbo closing. 3rd stage boost pressure should be any where from 18-32 psi depending on rpm and demand that the engine sense's. Higher rpm, steeper hill, heavy load, the higher the boost\backpressure will go. If it intermittently drops after repairing\replacing solenoids and harness and proper adjustment then I'd take a good hard look at the VG turbo air circuit and the control module especially. like I said this will normally be accompanied with intermittent low pulling boost.
that could be a problem in CM871 but CM870 doesn't come with VGTurbo. I'm wondering what's MR. R A W Z E thoughts about my issues.
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02-12-2019, (Subject: CM870 Jake problem ) 
Post: #6
RE: CM870 Jake problem
(02-12-2019 )DKenworth Wrote:  
(02-11-2019 )Chamberpains Wrote:  It could also be the turbo actuator control module. These things fail intermittently causing these exact symptoms. Are you experiencing intermittent low boost pressures while pulling? Could be an avenue to chase.The jakes are assisted with the VGTurbo closing. 3rd stage boost pressure should be any where from 18-32 psi depending on rpm and demand that the engine sense's. Higher rpm, steeper hill, heavy load, the higher the boost\backpressure will go. If it intermittently drops after repairing\replacing solenoids and harness and proper adjustment then I'd take a good hard look at the VG turbo air circuit and the control module especially. like I said this will normally be accompanied with intermittent low pulling boost.
that could be a problem in CM871 but CM870 doesn't come with VGTurbo. I'm wondering what's MR. R A W Z E thoughts about my issues.

I CAN TYPE IN CAPITAL BIG LETTERS TOO. YOU SHOULD READ UP ON YOUR ENGINE AND GET TO KNOW IT BETTER WHAT CHAMBERPAINS SAID IS TRUE AND 870'S COME WITH A FACTORY PNEUMATIC VGT TURBO AND IF IT NOT FUNCTIONING PROPERLY YOUR JAKES WILL DO THIS AND NOT FUNCTION PROPERLY.


User's Signature: 52 41 57 5a 45 20 53 4d 45 4c 4c 53
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02-12-2019, (Subject: CM870 Jake problem ) 
Post: #7
RE: CM870 Jake problem
An Cm870 does come with a vgt turbo, unless you have a Cm570 which would have a standard turbo..
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02-12-2019, (Subject: CM870 Jake problem ) 
Post: #8
RE: CM870 Jake problem
(02-12-2019 )DKenworth Wrote:  ...

that could be a problem in CM871 but CM870 doesn't come with VGTurbo. I'm wondering what's MR. R A W Z E thoughts about my issues.

your statement is incorrect...

The CM870 has an air-operated VG Turbo (Variable Geometry Turbo). On the CM870 engine in particular, it is notorious for acting up because it has an air actuation design + the ECU has no way of knowing if it is positioning correctly because there is no feedback for its operation.

In the CM871, they improved this problematic design with an electronic controller that does report the turbo's vane position back to the ECU to stop the exact problems others are trying to point out to you.

So,... this now leads to the question,.. does YOUR PARTICULAR ENGINE have a VG turbo on it? -- According to this picture you posted...


reference: http://rawze.com/forums/showthread.php?t...6#pid17816

I see an Air actuator on your turbo,.. IT IS an air operated VG Turbo, as the picture shows the top of the actuator + air-line feeding it behind the rag covering the rest of the turbo area. - This means that it very well could be doing what others are saying.

Maybe take a trip to Mr. Hags shop at some point to get some help with what it is doing if you can't figure it out. Also perhaps to ensure that whatever de-mandate programming the engine may have in it is not causing it.


User's Signature: ->: What I post is just my own thoughts and Opinions! --- I AM Full Of S__T!.
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