Please help PacBrake 05 Knight 330 ISC

[JDT]

When my dash tach was reading 2200, or close to it anyway, the info from the engine computer was showing 2350 to 2400. It was hard to keep the tach lined up, watch the computer and drive. So, 200 over what the dash tach says may be about right.

[Denali]

Originally Posted by Flagelpater

... Also, any help in getting to the correct person would be help also, I can hear the words of an Allison Tech Rep at a FMCA seminar saying "the RPM Limit Down Slope is 2650, and you are responsible for any overspeed if you are in 6th gear! apply the Service Brakes to keep the RPM within the limits."

That doesn't make sense.

In sixth gear you would need to do well over 100 MPH to approach the max RPM of the engine.

Both our current ISC 350 and our previous ISC 330 upshifted at 2650 RPM on downgrades.

BTW, I replaced our original Pacbrake with the newer PXRB model last year when the original unit broke. Unlike before, I can now maintain 55 MPH on 6% downgrades in fourth gear without using the service brakes.

[Denali]

Originally Posted by Flagelpater

FWIW Looks like I am at the "end of the road!" John at Cummins, after many emails, has told me that the ISC is limited to 2200 RPM even for PacBrake Operation. The 2600 RPM has been changed to the lower range for some unknown reason, he gave fuel economy but that does not make any sense to me. Be that as it may, unless some of you operators have info to the contrary, I am stuck with higher use of the service brakes. Thank you to everyone that has tried to help.

Both of the ISC engines with Allison MH3000 transmissions that we have had were limited to around 2200 PRM under load, but not when descending grades. When descending, they upshift at 2650 RPM.

I assume that the 2200 PRM limit would also apply if you simply floored it in Neutral, but I'm not going to test that.

[Flagelpater]

Denali Thank you for your reply. It appears that Cummins made a change sometime after 2004, lowering the RPM to 2200 for both Load Limit and No Load Limit. It would be nice to hear from someone that has a later Cummins ISC operating at the 2600 RPM.