General Boards > Technical Support
Previous Jake Brake thread
Joel Weiss:
A couple of months ago there was a thread in which concern was expressed about C-12 engines being subjected to "higher than redline" situations when using the Jake (compression) brake under certain circumstances.
There is a similar current thread on the irv2 forum in which the same concerns are expressed relative to Cummins engines. The situation being described is exactly the same as we had discussed here--whether the 4th gear downshift when the Jake is activated can result in an "over redline" situation. The key difference is that Cummins has stated that there are different redlines for acceleration and deceleration and that the engines can withstand significantly higher rpm's in the latter case without concern. http://www.irv2.com/forums/f123/engine-brake-usage-110054.html
I was curious if this issue had ever been discussed directly with someone at CAT? It's hard to imagine that CAT and Cummins engines would be significantly different in their behaviors with regard to this issue. I personally don't have a problem since I can engage the Jake at speeds up to 65 without concern about exceeding redline anyway, but I thought raising this issue in the context of the Cummins information might be useful to others.
Ken Buck:
My Cat C9 will not accelerate past 2150 with the foot throttle. The book says not to rev it past 2900 going downhill.
Ken
I guess I should add that 2150 is what it looks like the tach reads. I should look at the Alladin I guess and find out exactly some day. Also I think all the C9's technically use an exhause brake, not a true Jacobs exhaust valve opening Jake brake.
Dick Simonis:
I seem to recall my Cat C-12 manual says something about that. I'll double check but it stuck in my mind that the RPM limit was 2300 without a Jake brake and 2100 with a Jake. I have noticed that the downshift will not occur until the speed is low enough to not exceed 2300. Intuitively, it would seem that if Cat were concerned they would have dropped the shift point so a donwshift would simply not occur that allows an overspeed.
Joel Weiss:
--- Quote from: Dick Simonis ---I seem to recall my Cat C-12 manual says something about that. I'll double check but it stuck in my mind that the RPM limit was 2300 without a Jake brake and 2100 with a Jake. I have noticed that the downshift will not occur until the speed is low enough to not exceed 2300. Intuitively, it would seem that if Cat were concerned they would have dropped the shift point so a donwshift would simply not occur that allows an overspeed.
--- End quote ---
That's what I would have thought, also. But there were some pretty strong comments posted here about engine damage. I think the issue started with one or more individuals who believe their engines were damaged from an overspeed situation.
Marty and Suzie Schenck:
There are under load and under no load rpm's for diesel engines. The under load rpm for the C-12 is 2100 and the under no load rpm is 2150. This is right from CAT @ 1-877-777-3126. So if you are going 65mph or faster and engauge the Jake Brake on a Thunder or Marquis and it downshifts to 4th gear you run the risk of over reving the engine. That is one reason I had the default gear changed to 6th. No chance of over reving and I can control the braking gear. Marty
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