Right-hand (passenger) side of the case, midway back, just above the oil pan rail. Heavy-duty construction, fire apparatus, severe-duty trucks
Look for a small, colored rectangular plate on the right-hand or left-hand side of the main case. Allison Transmission Serial Number Lookup
Gently clean the plate with a mild degreaser and a nylon brush. Avoid wire brushes, which scratch the stamped text. If the plate is gone, look for a secondary laser-etched matrix code or serial stamp directly on the metal housing surface near the original tag location. Right-hand (passenger) side of the case, midway back,
Modern Allison ID tags are usually silver with black text, though older models may feature blue or green tags. The tag contains several key pieces of data: Right-hand (passenger) side of the case