The Allison 3000 series automatic transmission or the older label "MD3060" in my opinion is an excellent design. The modules come off one at a time and they are really quite easy to work on. You need the right tools and manuals of course but gone are the days of balls, springs and extra assembly parts that were common with older auto transmissions.
The photo below reveals the turbine sensor which is internal. The bottom of these transmissions have an aluminum cast unit called the control module. It has all of the solenoids and valve body that controls shifting. The code we had was a turbine sensor which stopped working only at certain times during a bus run. The turbine sensor being a winding which delivers the turbine speed signal to the transmission control unit was failing when the oil temperature got to a certain level.
Click on Each Photo to Enlarge
Using the Allison DOC software we were able to go on a road test and observe the turbine speed sensor and exactly what it was doing. The graph you see below in the photo show the activity of the output speed, engine speed and turbine sensors. These three signals are what the TCU reads to send the right information to the control module during operation for a proper shift at the right time and in the correct range.
Looking at the laptop image (click on the image to see more detail) you can see how great it is to be able to watch what the components are doing which makes it really easy to troubleshoot. What happened eventually when the transmission temperature got to around 140 degrees the turbine sensor flat lined on the graph reading causing the shifting to fail. At that time it was confirmed that the turbine speed sensor needed to be replaced and the labour to re and re the control module would not be wasted.
The control module is around 50 pounds so you need a tranny jack for sure. There are 2 dowels that line up the module to the main case and it's a bit of a fight prying the module down on to the jack. With some care it can be done including the removal of the wiring harness which slips through the access hole in the transmission case.
Once the sensor was replaced along with the necessary gaskets and seals the module was reassembled with new filters and sump suction filter (internal). The synthetic oil was added then running checks were performed. The road test was a success and the bus went back into service. Synthetic ATF oil is worth every penny in my book with anti foaming and heat resistant properties far superior than standard oils.
Valve body and shifting solenoids from the control module
Here is a link to the Mechanic's Tips Handbook in pdf form. It has very good general information with torque specs for servicing and other useful tips.
3 comments :
Hi John, thank you for the time you spend sharing your expertise.
I am working on a 1994 Monaco dynasty with cummins 8.3 and Allison md3060 with push button shift pad. Problem is: "do not shift" dash light illuminated and shifter display on, then flickers, then off. And shifter pad only gives me 10 seconds on IF I heat it with blow dryer. No shifter pad display if room temp or colder.
I will try to heat it again in the morning and get codes by pushing "up and down" buttons simultaneously
Any thoughts?
check the supply voltage to the shift pad. It comes directly from the main batteries 12 gauge wiring positive and negative. It then changes to several 18 gauge wires under the dash. Just make sure there is no voltage loss / drop. check the code reading as well code 35 00 is low battery.
I have volvo fl6 with allison and he have really slow start.In volvo service say that no error but that truck start slow and with no power,after 1700rpm when turbine work going better.Turbine is new,engine is new but nobody dont hawe answerwhy dont have power
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