335i Diff Retrofit Ford: Everything You Need to Know

If you’re a car enthusiast looking to enhance the performance of your BMW 335i, one of the upgrades you might be considering is a differential swap. Specifically, a popular modification is the “335i diff retrofit Ford” upgrade, where you swap out the factory differential with a more robust Ford 8.8 differential. This swap is particularly common among owners of BMWs from the E8x and E9x chassis, which includes the 135i, 335i, and even the M3 models.

This article will guide you through the entire process, explaining what a differential swap entails, why it’s worth considering, and how you can perform the retrofit effectively. We’ll also address related FAQs, giving you a complete understanding of the process.

Why Perform a 335i Diff Retrofit with a Ford 8.8?

The factory differential in your BMW 335i is built for everyday driving. However, it can become a weak link if you’re pushing your car’s performance to the limits, whether it be through high horsepower modifications or hard driving. Upgrading to a Ford 8.8 differential offers several advantages:

1. Stronger Build: The Ford 8.8 is known for its durability, especially in high-torque and horsepower applications. It’s used in many Ford Mustangs, which are performance-focused vehicles.
2. Affordability: Compared to other aftermarket differentials, the Ford 8.8 is relatively affordable while still offering great performance.
3. Better Support for Upgrades: If you’re planning more modifications, like turbocharging or supercharging, the Ford 8.8 diff can handle the added power better than the stock BMW differential.
4. Increased Traction and Control: The improved traction helps with performance in racing and high-speed conditions, making your 335i more predictable and easier to handle.

What Do You Need for a 335i Diff Retrofit?

When you’re swapping in a Ford 8.8 differential, there are several components you’ll need to make the retrofit successful. Here’s a breakdown of what’s required:

1. Differential Adapter Brackets: These are crucial because the mounting points on a Ford 8.8 diff are different from those on the BMW 335i. Adapter brackets allow the Ford diff to fit seamlessly into the BMW’s chassis.
2. Driveshaft: A single-piece driveshaft is often used during the swap. The stock BMW driveshaft won’t fit the new differential without modification, so a custom driveshaft designed for this retrofit is essential.
3. Axle Stubs: Billet axle stubs are stronger than the stock ones and ensure that the axles can handle the increased power and torque that the Ford 8.8 differential provides.
4. Carbon Fiber Components (Optional): Many enthusiasts opt for carbon fiber driveshafts or other lightweight components to reduce weight and improve performance.

Steps to Perform a 335i Diff Retrofit Ford

Here is a simplified guide to performing the Ford 8.8 retrofit on your BMW 335i. Keep in mind that this process requires mechanical knowledge, so it’s recommended to have some experience working on cars or consult a professional.

1. Preparation and Tools:
   • Ensure you have all the necessary components, including the Ford 8.8 differential, adapter brackets, driveshaft, and axle stubs.
   • Gather tools such as a torque wrench, jack stands, socket set, and possibly a lift if available.
2. Removing the Stock Differential:
   • Start by safely lifting the car and removing the rear wheels.
   • Disconnect the driveshaft from the stock differential, as well as the axles and any electrical connections.
   • Unbolt the stock differential from its mounting points and carefully remove it.
3. Installing the Adapter Brackets:
   • Install the differential adapter brackets into the BMW’s chassis. These brackets are designed to align with the Ford 8.8 diff mounting points.
4. Installing the Ford 8.8 Differential:
   • With the adapter brackets in place, mount the Ford 8.8 differential into the BMW’s rear subframe. Use the appropriate bolts and torque them to the manufacturer’s specifications.
5. Driveshaft Installation:
   • Install the single-piece driveshaft designed for the Ford 8.8 retrofit. This driveshaft connects the transmission to the new differential. Ensure that it’s aligned properly to avoid any vibration issues.
6. Axle Installation:
   • Install the billet axle stubs and connect the axles to the differential. Ensure that all connections are secure and torque everything according to specifications.
7. Finishing Touches:
   • Reconnect any electrical sensors or ABS lines if necessary.
   • Install the wheels and lower the car to the ground.
   • Perform a test drive to ensure that the retrofit is successful and that there are no unusual noises or vibrations.

Performance Improvements After the 335i Diff Retrofit Ford

Once you’ve completed the 335i diff retrofit with the Ford 8.8 differential, you’ll notice significant improvements in performance. Here are some key benefits:

1. Increased Durability: The Ford 8.8 diff is designed to handle high power outputs, meaning it won’t wear out as quickly under extreme conditions like the stock differential.
2. Improved Traction: With a stronger differential, your car will experience better traction, especially in high-performance driving scenarios such as track racing or drag racing.
3. Reduced Wheel Spin: If you’re running more horsepower in your 335i, the stock differential might allow too much wheel spin, reducing traction. The Ford 8.8 helps in controlling wheel spin, providing more power to the ground.
4. Enhanced Driving Experience: Overall, the car will feel more stable and responsive, allowing you to enjoy high-performance driving with confidence.

Common Issues and How to Address Them

While the 335i diff retrofit is a popular modification, there are a few challenges and issues that can arise during the process:

1. Fitment Issues: Since you’re retrofitting a part from a different car, you might encounter minor fitment issues. Adapter brackets usually solve this, but sometimes adjustments are needed.
2. Driveline Vibrations: If the driveshaft or differential isn’t aligned properly, you may experience vibrations when driving. Double-check all alignments during installation to avoid this issue.
3. Axle Compatibility: Ensure that the axles are compatible with the new differential. Using billet axle stubs helps, but it’s important to verify compatibility with your specific car model.
4. Gear Ratio Changes: Swapping to a Ford 8.8 diff may affect the gear ratios, which can alter how your car accelerates and handles. You may need to adjust the gear ratio to suit your driving style.

FAQs About 335i Diff Retrofit Ford

1. What is a differential retrofit? A differential retrofit is when you replace the stock differential in your car with a different one, often to improve performance. In the case of the 335i, the Ford 8.8 is a common upgrade for better durability and power handling.

2. Why use a Ford 8.8 differential for a BMW 335i? The Ford 8.8 differential is stronger and more affordable compared to other options. It can handle higher horsepower and torque, making it ideal for modified BMWs like the 335i.

3. How much does it cost to perform a 335i diff retrofit Ford? The cost varies depending on parts and labor. Typically, the parts (differential, driveshaft, brackets) cost between $1,500 to $2,500. Labor can add another $500 to $1,000 depending on your location and mechanic.

4. Can I perform the retrofit myself? Yes, if you have mechanical experience and the necessary tools. However, it’s recommended to consult a professional if you’re unsure, as this is a complex modification.

5. Will the retrofit affect my BMW’s warranty? Yes, modifications like a differential swap will void your BMW’s warranty on related drivetrain components. Be sure to consider this before performing the retrofit.

6. What are the benefits of a single-piece driveshaft in this retrofit? A single-piece driveshaft is lighter and more efficient than a two-piece. It reduces rotational mass, improving acceleration and response.

7. How long does the 335i diff retrofit take? The retrofit typically takes a few hours to a full day, depending on the experience level of the person doing the work.

8. Will this retrofit improve my 335i’s performance on the track? Yes, the Ford 8.8 differential offers better traction and durability, making it an excellent choice for track performance.

Conclusion

Performing a 335i diff retrofit Ford is one of the most effective upgrades you can make to your BMW 335i, especially if you’re increasing its power output or driving it in high-performance situations. The Ford 8.8 differential is stronger, more affordable, and capable of handling the demands of a modified car. While the process requires mechanical expertise, the benefits in terms of durability, traction, and overall driving experience make it worth the investment.

With the right components and a well-planned installation process, you can transform your BMW into a performance machine that’s ready to tackle any challenge.