Heads up on output sensor
I was having some minor anomolies, idle rpm occasionally surging very much like air in fuel but determined there was no issue with fuel. Then the cruise (original cruise king and throttle) became semi functional, making me deeply suspicious of this system. But the run up to San Antonio from Port Aransas was just fine. We got loaded up, headed for the Olympic Peninsula, pulled out of the RV park, what is this? Shiftpad shows wonky, speedometer dead, and we're locked in first gear. Fortunately, turning engine off, restarting allows a shift into reverse, repeating this gave us first for a grand U turn on highway and back into park.
Appears to be an output speed sensor, browsing the interwebs. What is greatly lacking in available information is detail for the sensor for retarder model 3060R Allison. It is very different from the sensor for a non retarder 3060. After mistakenly replacing the only sensor visible on trans, which turned out to be the input speed sensor, and finding no improvement I began the long process of vetting the wiring, rear to front. Looking at this wiring I'm thinking....it's rock solid. Well done, wrapped twisted pairs in mylar and loom, I cleaned the connections. While pondering the underside of tranny, I realized that the output speed sensor would be on output end of transmission, right?
Aha! On the side of the retarder is a four bolt plate on an enclosure that is noted as a watertight junction box by Allison docs. Removing this the output sensor is readily available. I installed the new sensor, checked the resistance between pins at computer up front, Voila! Spec. 350 ohms. Reconnected batteries, (the Transmission Instrument guys recommend disconnecting batteries before unplugging wiring from computer, Allison does not mention this), reconnnected computer, buttoned up and test drove. Perfect.
Here are a few takeaways:
Shift points are changed for the better. Higher shift points accellerating, lower downshift points. A sense of more power. Speedo working.
Fuel mileage has improved markedly. Getting out of the hellish heat in Tx, I drove it like I stole it. Lots of 70 MPH cruising on interstates, through the rockies, on through Wyoming, I am averaging 8.9 mpg, compared to historical 8.25 while driving more sedately.
Cruise King functioning flawlessly.
The sensor part # is 29543434 from Stewart and Stevenson. $435.00 out the door. Hecho in Mexico. The Chinese version is readily available on Ebay, $50.00. I figure 435.00 is not a bad deal for bringing a dead transmission to life, and it was in stock. I'll probably pick up one of the asian version to keep in spare parts.
Topic: Heads up on output sensor