Identifying a Transmission
Short answer: Decoding the markings you listed: 3925647 is the case number for a 3-speed; F288 is a date code (June 28, 1968); 18S273731 is the VIN of the car it came in (18 = St. Louis, 1968).
A Muncie would typically be stamped like “P7J25” (P = Muncie, 7 = 1967, J = Oct, 25 = day); shift arms attached with studs/nuts up to 1969, bolts after. The 1967 Firebird offered two 3-speeds: the standard Saginaw and the heavy-duty Dearborn (Warner) — the Warner was only behind the 400, so everything else (including the 326 H.O.) got the Saginaw. If that trans is original to your 326 H.O., it’s a Saginaw.
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Content last modified: June 13, 2026 at 10:06 am
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