* Brake type: Did the car have power brakes or manual brakes? Power brakes often used slightly larger wheel cylinders.
* Rear axle: Different rear axle ratios and options might have called for different wheel cylinder sizes.
* Specific model within the Catalina line: Even within the Catalina line, there could be variations based on trim level or options.
To determine the correct size, you need to:
1. Check your car's parts manual: This is the most reliable source. A Pontiac Catalina parts manual specific to the 1966 model year will list the correct wheel cylinder bore size(s) for your particular vehicle.
2. Check the wheel cylinder itself (if still installed): The size is often stamped or cast onto the wheel cylinder. Look for a diameter measurement (e.g., 1-inch, 1 1/16-inch).
3. Consult a parts supplier: Provide them with your car's VIN (Vehicle Identification Number). They can then look up the correct parts, including the wheel cylinders.
Without knowing the specifics of your 1966 Pontiac Catalina, it's impossible to give you a definitive answer.
