: Many trucks feature a white placard on the driver’s side door frame or cab/cowl that lists the transmission model and serial number.

If the plate is unreadable, you can often narrow down the model by the first few digits of the serial number provided by retailers like Dartco Transmission : Starts with 631, 632, or 9308. 3000 Series: Starts with 651, 652, or 9307. 4000 Series: Starts with 661, 662, or 943.

"Serial number," Renny muttered. "It’s the only way to get the right parts. If you guess, you buy a thousand-dollar paperweight."

: The serial number is usually 10 digits long and is listed on the bottom left of the data plate, directly under the model number. Quick Identification by Serial Prefix Common Allison series often start with these digits: 1000/2000 Series : Starts with 3000 Series : Starts with 4000 Series : Starts with Dartco Transmission

| Need | Action | Link / Method | | :--- | :--- | :--- | | | Look at data plate on transmission case | Physical inspection | | Basic Warranty Check | Use Allison's public warranty page | allisontransmission.com/parts-service/warranty | | Full Parts & Service Data | Subscribe to Allison DOC | allisontransmission.com/parts-service/service-tools | | Quick Model ID by SN Prefix | Decode manually (see Part 3 above) | Use the letter-digit chart | | Help without subscription | Call authorized dealer | Search "Allison distributor near me" |