Early Bronco Automatic Transmissions

Early Bronco Automatic Transmission: Breaking Down the Options

Choosing the right automatic transmission for a 1966-77 Ford Bronco comes down to how you drive, how original you want to stay, and how much fabrication or wiring you’re willing to take on. From factory-correct classics to modern multi-speed automatics, Early Bronco owners have more options today than ever before. Below is a breakdown of the most common automatic transmission choices, along with real-world pros, cons, and use-case considerations.

Ford C4 Automatic

The C4 is the most straightforward automatic transmission option for an Early Bronco. It was factory-installed in many 1973-77 Ford Broncos and remains the go-to choice for restorations and simple upgrades.

This is a 3-speed automatic with no overdrive, meaning highway RPM will be higher compared to newer transmissions. The upside is simplicity—no electronics, no special controllers, and a true bolt-in installation when paired with the correct bellhousing, torque converter, and stock crossmember.

Best for: Factory restorations, mild builds, and owners who want a simple, proven setup with minimal installation hassle.

Ford AOD Automatic

The AOD is a popular upgrade for Bronco owners who want better highway manners without stepping too far into modern electronics. Similar in overall size to the C4, the AOD typically requires only minor modifications to fit.

Unlike the C4, the AOD adds overdrive, which significantly lowers cruising RPM and improves fuel economy on the freeway. It’s a mechanically controlled transmission, so no standalone controller is required—though correct TV cable geometry is critical for transmission life.

Best for: Street-driven Broncos, daily drivers, and long-distance cruisers looking for overdrive without complex wiring.

Ford C6 Automatic

The C6 is Ford’s heavy-duty automatic transmission and is built to take abuse. It’s physically larger and heavier than the C4 or AOD, and installation in an Early Bronco is more involved due to its large size.

Like the C4, the C6 is a 3-speed automatic with no overdrive. Its strength makes it appealing for high-horsepower engines, big tires, and hard off-road use, but the tradeoff is added weight and higher cruising RPM. 

We generally only recommend the C6 if you need the strength and insist on an automatic transmission. Otherwise, there are some really great manual transmission options that are easier to install and offer the strength needed for heavy use applications.

Best for: High-power builds, aggressive off-road use, and owners prioritizing strength over fuel economy.

Ford 6R80 Automatic

The 6R80 brings modern performance to the Early Bronco platform. This 6-speed automatic offers tight gear spacing, improved drivability, and excellent highway performance thanks to multiple overdrive gears.

Most commonly used in Coyote swaps, the 6R80 can also be adapted to work behind a factory Small Block Ford with the proper adapter components. Installation is more complex than older automatics and requires a standalone transmission controller along with additional wiring and setup time. There are a lot of 6R80's being run in classic Broncos, so finding support online if you hit a snag is relatively easy.

While the 10R80 10-speed automatic is another modern option, aftermarket transmission controllers for it are currently limited, making it a less practical choice at this time.

Best for: Modern engine swaps, performance-focused builds, and owners comfortable with wiring and electronic controls.

Additional Automatic Transmission Options to Consider

There are several other automatic transmissions that come up in Early Bronco discussions. While less common, they may fit specific build goals:

Ford AOD-E

Electronically controlled version of the AOD. Offers similar gearing and overdrive benefits but requires a transmission controller, adding cost and wiring complexity. Shifting can be more precise than a mechanical AOD when properly tuned.

Ford 4R70W

An evolution of the AOD-E with improved internals and better gear ratios. Popular in restomod builds, but like the AOD-E, it requires a standalone controller and additional wiring.

GM 700R4

A 4-speed automatic with overdrive commonly used in GM swaps. It can be adapted to Ford engines, but doing so introduces cross-brand components, adapters, and potential parts compatibility issues. Typically chosen only when a GM drivetrain is already part of the plan.

Which Automatic Transmission is the Best Option for an Early Bronco?

There’s no single “best” automatic transmission for an Early Bronco—only the best option for how you plan to use it. Whether you’re restoring a classic, building a highway cruiser, or stuffing modern power under the hood, understanding the strengths and limitations of each transmission will help you build a Bronco that drives the way you want it to.