I apologize for writing a long post, but my Beaver and I are under stess!
For some reason, Beaver forgot to put a Cat in my 2004 Monterey. I have a Cummins ISC 350. As a newbie when I bought it, I didn’t know better. Except for a $600 fuel filter, the drive train has been flawless for almost 80,000 miles. Even though I don’t have a Cat, maybe you can still help me!
After having a lot of fun at Jim and Gerda Bull’s rally in Grants Pass last week, we drove north on I-5 towards Ellensburg for a Jazz Fesitval. For the first time in 80,000 miles, the Pacbrake malfunctioned.
On the first downhill grade, I switched on the Pacbrake. The cruise control disengaged, the RPM kicked up and I felt the braking effect. Then, for no apparent reason, it up shifted, the RPM dropped and the braking effect went away. A few seconds later, the Allison down shifted again and the braking effect returned.
Puzzled by the abnormal behavior, I put the Aladdin engine page in the primary scan. On the next downhill grade it did it again. I had engaged the Pacbrake with the switch, the Aladdin showed that “2” was selected and it down shifted to “4” from “6”. After about a half minute, the selected gear changed from “2” to “6” , the Allison shifted and the braking effect went away. Then it reselected "2" and went back to normal down grade operation. The abnormal pattern repeated itself on the next couple of downgrades.
Befuddled, I phoned Marty Schenk on my (hands free!) cell phone to brainstorm. I don’t know if he knows anything, but I had him on speed dial (grin!). The chassis voltage was fluctuating from 13.8 to 14.1 and my chassis batteries are 7 years old so I had convinced myself the computers were not happy with that. Marty talked me out of that idea. We agreed that a shut down and restart at the next rest stop might re-boot the computers. He also remembered a thread on the Cat board about a faulty relay.
I pulled into the next rest stop, shut down, did the usual walk to the back of the motorhome, returned, restarted and pulled out to attack the next hill. On the next couple of downhill grades it repeated the same bad behavior. The re-boot didn’t work.
It occurred to me that, instead of letting the Pacbrake do it, I could tell the Allison what to do with the arrow buttons on the keypad. On the next downhill grade I engaged the Pacbrake, verified that the cruise control canceled, verified that “2” was selected, watched the shift to “4”, pushed the down arrow 4 times (to back up the Pacbrake signal) and waited. It worked normally. There was no “hunting” of the “selected” gear. At the bottom of the hill I disengaged the Pacbrake, pushed the “D” button to end the “2” selection and reengaged the cruise control. This worked consistently on the next couple of downgrades.
To further the troubleshooting, I tried switching the Pacbrake off and on a down grade while the transmission was selected to “2” with the arrow key. I could feel the braking effect change confirming the Pacbrake valve was operating.
Soon, I was out of the hills of southwest Oregon and am satisfied that I can continue to drive safely by backing up the Pacbrake by downshifting with the arrows.
My theory is that the Allison is working properly as long as it gets the a command from either the Pacbrake or the arrow keys. I think that the Pacbrake may be sending an initial downshift signal to the Allison, but then the signal drops out. That suggests the wiring from the dash switch is OK to the Pacbrake, but not to the Allison.
What sends the signal to the Allison? Does it come from the dash switch, the Pacbrake or a relay? Where should I look for the simple stuff like wires and fuses? What other ideas might you have? Where are the best Pacbrake technicians in the Northwest?
Thanks in advance!
Bill
PS: I’m looking forward to seeing a lot of you in Harrisburg!