How to Determine the Differential Size in BMWs Up to 1999

Knowing the size of your BMW’s differential is crucial for maintenance, repairs, and upgrades. If you own a BMW made up to 1999, you can easily determine the differential size by counting the bolts on the side caps holding the differential carrier. This guide will help you identify the differential size and provide examples of specific models where these differentials were typically found.

Identifying Your BMW Differential Size

BMW differentials up to 1999 come in three sizes, known as Type MM differentials. Here’s how you can identify them:

1. 168mm Differential (Small Case)

   • Identification: 4 bolts on the side caps.
   • Common Models: Found in BMW E30, E36, and Z3 models with 4-cylinder engines.
   • Example: BMW 318i (E30/E36), BMW Z3 1.9.

2. 188mm Differential (Medium Case)

   • Identification: 6 bolts on the side caps.
   • Common Models: Typically found in BMW E30, E36, E28, E34, E32, and Z3 models with 6-cylinder engines.
   • Example: BMW 325i (E30/E36), BMW 528i (E28/E34), BMW 735i (E32), BMW Z3 2.8.

3. 210mm Differential (Large Case)

   • Identification: 8 bolts on the side caps.
   • Common Models: Found in high-performance and V8 models, including E36 M3 3.2, E34 V8 and M5, E32 V8, E39 M5, E24 M6, E28 M535i and M5.
   • Example: BMW M3 3.2 (E36), BMW 540i and M5 (E34), BMW 740i (E32), BMW M5 (E39), BMW M6 (E24), BMW M535i and M5 (E28).

Why Knowing Your Differential Size Matters

Understanding the size of your differential helps you in several ways:

• Maintenance: Ensures you get the correct parts for servicing.
• Upgrades: Helps you choose the right performance upgrades, such as limited-slip differentials (LSD) and differential covers.
• Troubleshooting: Simplifies the process of diagnosing issues related to drivetrain components.

How to Count the Bolts

To determine the size, locate the differential and count the number of bolts on the side caps that hold the differential carrier. This method is quick, straightforward, and accurate.

Conclusion

Whether you’re a DIY enthusiast or a professional mechanic, knowing how to identify your BMW’s differential size is a valuable skill. By following this guide, you can ensure you’re well-prepared for any differential-related tasks. For high-quality LSD conversion kits and other differential upgrades, visit RacingDiffs.