* Original Rear End Width: First, determine the width of your El Camino's *original* rear end. This is crucial for finding a replacement that fits properly. Measuring from flange to flange is the best way to do this.
* Housing Width of Replacement: The replacement axle housing must match or be very close to the original width. Using a rear end that's too wide or narrow will require significant modifications to the chassis, including potentially modifying the spring perches or even the frame itself—a significant undertaking.
* 10-bolt vs. 12-bolt: While both are common in GM vehicles, the 12-bolt is generally stronger and better suited for higher horsepower applications. A 10-bolt is perfectly adequate for many street-driven El Caminos. Both came in various widths.
* Year and Model of Donor Vehicle: The year and model of the car the rear end comes from will influence the width and other characteristics. You'll need to research rear end widths for various GM vehicles from the same general era (late '60s, '70s, and possibly early '80s) to find a compatible match.
Finding a suitable replacement:
1. Measure Your Original: As stated above, the most important step is measuring the width of your existing rear end.
2. Research: Once you know the width, you need to research which GM vehicles from the relevant era used rear ends with similar widths. Online forums (like those dedicated to classic Chevrolets) and parts catalogs are your best resources.
3. Consider Spring Perches: Even if the overall width is close, the spring perch location might differ slightly. You may need to have the perches modified or relocated to fit your El Camino.
4. Brakes and Suspension: Ensure the brakes and suspension components (such as the shock mounts) are compatible. You might need to adapt or replace some parts.
In short, there's no single answer. The best approach is to measure your existing rear end and then research which GM rear ends (10-bolt or 12-bolt) from the appropriate time period have a similar width. Be prepared for potential modifications to ensure a proper fit. Consult with a specialist in classic car restoration if you're not comfortable with the process.
