What Transmissions Bolt Up to a Ford 300 6 Cylinder?by Rob Wagner
Three-speed manual transmissions are the best candidates to bolt to the 300-cubic-inch in-line six-cylinder engine in a Ford F-Series pickup truck. The Tremec T5 five-speed manual serves as a good upgrade for the 300.
T85 to T89 Manuals
The T85, T86, T87 and T89 three-speed manual transmissions can fit behind the 300 straight-six. Depending on the origin of the transmission, most will fit directly onto the 300 with few modifications. However, three-speeds from non-Ford vehicles or Ford automobiles may require modifications, according to Hemmings. Ford primarily equipped its Ford F-Series trucks with the 300.
Construction and Gear Ratios
The cast-iron T85 with a nine-bolt side cover bolts onto 1965 to 1971 Ford trucks with the 300. The T86 matches 300s in 1961 to 1964 trucks. The T87 transmitted power to the wheels from the 300 engine in all trucks through 1975. The T89 fits all Ford trucks through 1971. The gear ratios are 2.53-to-1 or 2.49-to-1 for first gear, 1.59-to-1 for second and 1.00-to-1 for third. The transmission shafts from cars must be exchanged for longer versions (half-inch) on trucks. The T-85-N matches the 300 without modifications.
The Tremec T5 five-speed is adaptable to the 300 with modifications. Transmission fabrication shops can manufacture adapters for the 300's 8.5-inch clutch and flywheel. The gear ratios are 2.95-to-1, 1.94-to-1, 1.34-to-1, 1.00-to-1 and 0.63-to-1.