jake brake question - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 5 (permalink) Old 10-14-2011, 05:17 AM Thread Starter
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jake brake question

I am new here and see that this is a valuable resource and a wealth of iinformation. I live in western Co in the mountains and all of my driving is in the hills and mountains. I have drove trucks loaded heavy with cummins engines, cat engines, detroit engines, and mack engine. My experience is that cummins has the strongest jake in the mountains, then detroit, then cat, then mack. What is the cause of one jake brake holding way stronger than another? I understand the theory of operation of a jake brake and in our area there are a lot of cats, cause they pull harder in the hills, but going down heavy, the cummins is always in the lead. Can anyone shed some light on this?
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post #2 of 5 (permalink) Old 10-14-2011, 11:03 AM
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I am not sure which engine has the best Jake but I think Jake is an independent manufacturer for all the trucks that you mentioned. However Mack has one by the name of power leash on the newer trucks.
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post #3 of 5 (permalink) Old 10-15-2011, 12:23 AM Thread Starter
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yes that is what is confusing to me. all the jake brakes are in theory the same design and the same components until the new cummins, which is supposed to have the strongest jake to date and they havean integrated design that is not of the same style or configuration as the old ones. The cat always had the bigger engine, 904 inch where the cummins was an 855 then cummins went to the 14L and cat has a 15L but thecummins still has stronger hold back. I am amazed by this and am not sure why but im sure there is a reason and I'll keep researching until i see if I can find the answer. Thanks.
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post #4 of 5 (permalink) Old 10-15-2011, 05:04 AM
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It has to do with the way the Jakes are actuated and the internal design of the motor. Cummins has a separate rocker arm for the injector, so they use that to provide actuation for the exhaust valve on the same cylinder. Cat uses an injection pump so there is no such rocker arm so they have to use the exhaust valve of a different cylinder and that is less efficient timing wise. Detroit 2 cycle does have an injector rocker but I think due to the loss of compression caused by the intake ports being in the cylinder wall they are not as great. I don't know about Macks. At least that's the way it was in the good old days.

Nowadays like you say I think the Cummins ISX has a separate cam lobe for Jake brake only? And some of them have Jake brake HP actually exceeding engine "go" power. That sure beats the olden days when if we were lucky we had a switch to make the fan turn on for retarding HP.

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post #5 of 5 (permalink) Old 10-16-2011, 03:09 AM Thread Starter
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I knew someone would know. Thanks That makes perfect sense to me on the operation of the systems. I now don't wonder and will continue researching the systems.
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