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Old 10-27-2020, 06:15 PM   #1
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Engine Break over reving engine

I have a Allison 3000 series Transmission mated to my Cat C7 on a Freightliner chassis. I have observed now on some longer grades, that the engine breaking function will allow the engine to exceed the stated redline of 2400 RPM. Is this considered normal operation.

I have also noticed that if I apply the service break to slow down, the transmission continues to down shift and pulls the RPM right back up to red line. I am concerned that this is going to damage the engine.

Thanks in advance
Jim Brinsfield
07 Fleetwood Excursion
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Old 10-27-2020, 06:24 PM   #2
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Engines have a different "permissible RPM" while working/under load than under no load/no fueling conditions.

Call Caterpillar (877 777-3126) with your engine serial number to find out ALL of the following:

Peak torque RPM
Max Governed RPM
Max No-load RPM

Commit those numbers to memory!
Brett Wolfe
Ex: 2003 Alpine 38FDDS. Ex: 1997 Safari Sahara. Ex: 1993 Foretravel U240
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Old 10-28-2020, 12:33 PM   #3
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I think you might be talking about an Exhaust Brake system and it works best at high RPM. Mine upshifts if it is above 2400.
Rick and Larrie Dee
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Old 10-28-2020, 12:37 PM   #4
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Much better thread than what I expected. I read it as "Engine Broke Over Reving Engine."
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Old 10-28-2020, 12:37 PM   #5
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RED Line RPM are based on engine 'under load' conditions
Engine Brake/Exhaust Brake RPM...engine NOT under load...higher RPM allowed
ECM will NOT allow engine damage when using engine/exhaust brake
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Old 11-04-2020, 12:05 AM   #6
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My 3126B, 3000 series will upshift at 2650 RPM, during exhaust brake operation.
When I need to apply the service brake at 2500 , I only drop the RPM to 2000.
Below 2000 the trans / exhaust brake program will downshift to a lower gear; to keep the engine RPM in the optimal exhaust brake performance range.
The exhaust brake performance graph , is the last in the attached pdf. The chart goes to 2900 rpm and that's the manual transmission equipped engine's max operational RPM when using the exhaust brake.
Attached Files
File Type: pdf 3126B specs.pdf (113.9 KB, 6 views)
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
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