What size is the rear axle on a Chevy Silverado 1500?
The vast majority of Chevy Silverado 1500 pickups use a 9.5-inch rear axle (ring gear diameter). The exact size can vary by year and configuration, but the 9.5-inch rear axle is the standard for most light-duty Silverado 1500 models. Larger rear axles are reserved for the heavier Silverado 2500HD/3500HD line.
Common rear-axle size for the Silverado 1500
Below is a quick guide to the typical rear-axle configuration you’ll find on most Silverado 1500 trucks. This helps explain what you’re likely to encounter, depending on year and drivetrain.
- 9.5-inch ring-gear rear axle (approximately 241 mm) — standard on most light-duty Silverado 1500s across recent generations. It supports a range of final-drive ratios depending on engine and drivetrain, such as 3.23, 3.42, 3.73, and 4.10 in various configurations.
- 10.5-inch rear axle — used on the heavy-duty Silverado 2500HD/3500HD, not the 1500. If you’re shopping for a true 1500 model, this size is not part of the standard 1500 lineup.
Knowing the exact rear-axle size for a specific truck may require checking the vehicle’s documentation or VIN, as options and configurations can vary by year and trim.
How to verify the exact rear-axle size on your Silverado 1500
There are several practical ways to confirm the rear-axle size for a particular Silverado 1500 you own or are considering.
- Check the door jamb or glove box documentation and the vehicle’s build sheet or window sticker for the axle ratio and RPO codes.
- Use the VIN to look up the original equipment specifications through GM’s Official Parts or a reputable third-party VIN decoder to see the axle ratio and related options.
- If you have safe access to the rear differential, the ring-gear size can be determined by inspecting the differential cover and, if necessary, measuring the ring gear diameter after removing the cover (note: this requires proper caution and tools).
If you’re unsure, a Chevrolet dealer or a qualified mechanic can confirm the exact rear-axle size and gear ratio for a specific vehicle configuration.
Why the rear-axle size matters
Axle size and gear ratio influence towing capability, fuel economy, and acceleration characteristics. A taller highway-gear (e.g., 3.23) can improve fuel efficiency at cruising speeds, while a lower gear (e.g., 3.73 or 4.10) can enhance torque and towing performance. Understanding your RX (rear axle) helps when selecting options, planning towing, or evaluating aftermarket gear choices.
Summary
For most Chevy Silverado 1500 trucks, the rear axle is a 9.5-inch ring-gear unit, with gear-ratio options that vary by model and drivetrain. The larger 10.5-inch rear axle is exclusive to the Silverado 2500HD/3500HD heavy-duty lineup. To confirm the exact size on a specific vehicle, check the build sheet or VIN, and consult the dealer or a trusted service professional if needed.
How do you tell if you have a 7.5 or 8.5 rear end?
You can tell the difference between a 7.5 and 8.5 rear end by looking at the shape of the cover, the shape of the axle tubes, and the protrusions on the bottom of the housing. The 8.5 has a round cover with larger, rectangular protrusions at the bottom, while the 7.5 has a more squared or oval cover with smaller, crescent-shaped lugs at the bottom. Additionally, the axle tubes on an 8.5 are flared or stepped down as they enter the pumpkin, while the 7.5 has straight axle tubes.
This video shows how to visually identify a GM 10 bolt rear axle, including how to distinguish between a 7.5 and 8.5 rear end: 53sandhotrodshopYouTube · Dec 14, 2023
Visual differences
- Cover shape: An 8.5 has a round rear cover, whereas the 7.5 has a more squared-off or oval cover.
- Axle tubes: The tubes on an 8.5 will appear to swell or flare out just before entering the differential housing. The 7.5 has straight axle tubes.
- Bottom protrusions: The 8.5 has larger, rectangular "ears" or protrusions at the bottom of the housing (around the 5 and 7 o'clock positions). The 7.5's protrusions are smaller and more crescent-shaped.
Other methods
- Measure the bolts: On some GM 10-bolt rears, the distance between the bottom center bolt and the nearest bolt on either side can be used for identification.
- 8.5: The distance is approximately 3.753.753.75 inches.
- 7.5: The distance is approximately 3.253.253.25 inches.
- Check the vehicle's RPO codes: Look for a sticker in the driver's side doorjamb or glove box. The codes listed under "Axle" or "RPO" will specify the factory-installed rear end. This is the most accurate method if the rear end is original.
How to find rear axle size?
To measure a rear axle, you'll need to take several key measurements, depending on the application. The most common are wheel mount to wheel mount (WMS), which is the width from the outside of the brake rotor/drum mounting surface on one side to the other. You'll also need spring center to spring center for trailers, which is the distance between the mounting pads for the leaf springs. For specific axle types like bicycle thru-axles, you measure the diameter, length, and thread pitch.
This video demonstrates how to measure trailer axles, including hub face to hub face and spring center to spring center: 59setrailerYouTube · Jun 12, 2023
For trailers and most vehicles
- Wheel Mount to Wheel Mount (WMS):
- Remove the wheels and tires to make it easier, or use a tape measure from the back of the hub face on one side to the other.
- Alternatively, if the hubs are present, measure from the outside face of the brake flange on one side to the outside face of the flange on the other.
- Spring Center to Spring Center:
- Measure the distance between the center of one spring mounting pad and the center of the other.
- Axle Diameter:
- If your hubs are removed, you can also measure the diameter of the axle tube itself, which correlates to its capacity.
For bicycles
- Diameter and Length:
- Measure the diameter of the axle, which is typically a standard size like 12mm for thru-axles.
- Measure the overall length of the axle shaft.
- Thread Pitch:
- Measure the distance between the ridges of the threads. This is often a standard metric size, like 1.5mm or 1.75mm.
- For a more accurate measurement, you may need calipers, or you can use a thread pitch gauge.
- Frame/Fork Width:
- For thru-axles, measure the distance between the inside of the fork dropouts (front) or the frame dropouts (rear).
For specific axle shaft types
- Press-on Bearing Axles:
- Measure from the outside face of the hub (where the rotor or drum mounts) to the end of the shaft. Keep the tape measure parallel to the shaft for accuracy.
- Floater Axle Shafts:
- Measure from the back side of the flange (the mounting surface) to the end of the shaft.
What size rear differential is in a 2004 Chevy Silverado?
Chevrolet Silverado 1500 2WD or 4WD Rear Differential 8.6-Inch 1999-2004.
How do I know what axle my Silverado has?
Identify your GMC or Chevrolet rear end gear ratio by the RPO Codes, usually located on the placard labeled “Service Parts Identification” inside the drivers door panel or glove box. Note that using the RPO code for parts identification assumes that the rear end has not been previously modified!!
