To find the gear ratio for *your* specific 1985 Ford F-350, you need to:
* Check the Vehicle's Data Plate: This sticker, often located on the driver's side doorjamb, might list the axle ratio. Look for codes or numbers that indicate the ratio (e.g., 3.50, 4.10, 4.56).
* Inspect the Differential: This is more involved and requires getting under the truck. Look for numbers stamped on the differential housing itself. These numbers often indicate the gear ratio. You may need a flashlight and possibly a mirror. Online resources for Ford trucks can help decipher these markings if you find them.
* Review the Owner's Manual (if you have it): The original owner's manual may specify the axle ratio.
Without knowing your truck's specific configuration, it's impossible to give you the correct gear ratio.