What is the diff ratio for a Ford Cortina?
The Ford Cortina did not have a single, universal final-drive (diff) ratio. The ratio varied by model, engine, year, and market, typically falling somewhere in the 3.5:1 to 4.1:1 range depending on the axle option chosen by Ford for that particular car.
In this article, we explain the typical ranges you might encounter, how to identify the exact ratio for a given Cortina, and why the number matters for performance and fuel economy.
Understanding the final-drive ratio on the Cortina
The final-drive ratio describes how many times the driveshaft turns for one revolution of the wheels. It is a key factor in acceleration, engine RPM at cruising speed, and fuel consumption. Ford offered several axle configurations over the Cortina’s production span, so the exact ratio you’ll find on a car depends on its specific build sheet and market.
Common final-drive ratios found on Ford Cortina models
To give car enthusiasts and restorers a practical reference, here are representative final-drive ratios that appeared in Cortina literature and surviving examples. Note that exact figures should be verified on the individual vehicle, as options varied by year and market.
- 3.55:1
- 3.77:1
- 3.89:1
- 4.10:1
These values describe typical final-drive options. The precise ratio for a given Cortina is determined by its axle code and production specifications, so please verify on the car itself or in its factory documentation.
Notes on identifying the correct ratio
Because the Cortina used several axle configurations, the most reliable way to know your exact diff ratio is to read the axle code stamped on the differential housing or axle tag and cross-check it with Ford’s axle-code charts from the corresponding model year. If the code is unclear or damaged, you can also estimate the ratio by careful measurement of the driveshaft and wheel rotations, or by consulting the service manual or parts catalog for your specific Cortina variant.
How to identify your Cortina’s diff ratio
Use these steps to determine the exact final-drive ratio on your Cortina.
- Locate the axle code on the differential housing or axle tag. The code will indicate the gear set ratio (for example, values corresponding to 3.55, 3.77, 3.89, or 4.10).
- Match the code to the appropriate Ford axle-code chart for your model year and market in a factory manual or reputable catalog.
- If the code is unreadable, perform a ratio measurement by turning the input shaft once and counting how many times the output shaft (and wheels) turn, or use precise measurements of gear teeth and mounting geometry as outlined in service procedures.
- Record the final-drive ratio once verified, and note that some Cortina variants offered different ratios for different trims or markets.
Knowing the exact ratio helps with restorations, maintenance planning, and understanding how the car will behave at highway speeds or during acceleration.
Summary
The Ford Cortina encompasses several final-drive ratios rather than a single standard figure. Typical ratios seen in the fleet include 3.55:1, 3.77:1, 3.89:1, and 4.10:1. To be certain of a specific Cortina’s diff ratio, locate and decode the axle code on the differential housing or consult model-year catalogs and manuals. With the exact ratio in hand, you can better assess performance characteristics, gearing, and fuel economy for that particular Cortina.
What is special about Ford Cortina?
It had a unique 1558 cc twin-cam engine by Lotus, but based on the Cortina's Kent OHV engine. Aluminium was used for some body panels. For a certain time, it also had a unique A-frame rear suspension, but this proved fragile, so the model soon reverted to the standard Cortina semielliptical rear end.
What are Mk2 Cortinas worth today?
Typically, you can expect to pay around $10,400 for a 1968 Ford Cortina Mk II in good condition with average spec.
How do I find out what gear ratio my Ford rear end has?
To determine the axle ratio of your vehicle, locate the two-digit axle code first, then use your vehicle's towing guide to find the axle ratio that corresponds to that code. If your vehicle has a limited-slip differential, it will be noted as Limited Slip.
What is the rarest Cortina?
In 1977, the new MkIV Ford Cortina appeared in the James Bond film The Spy Who Loved Me. Although the fourth generation Cortina was the best-selling car throughout its production run it is now the rarest Cortina. It's thought that this could be down to poor rustproofing and how popular this model is with banger racers.
