Chevrolet Rear Axle Identification Chart: Gear Ratios and Differential Codes
There’s a certain kind of clarity that comes from knowing exactly what’s under your Chevy’s rear end—whether you’re towing a heavy trailer with your Silverado or tuning your Camaro for better off-the-line performance.
You’ve just bought a used truck and want to confirm it has the towing package, or maybe you’re planning a gear swap and need to know what’s currently installed. The numbers stamped on the axle tube might look like random code, but they tell you everything about your differential. We’ll show you exactly where to look and how to decode what you find.
TL;DR (Too Long; Didn’t Read)
Your Chevy’s rear axle ratio and differential type are identified by stamped codes on the right axle tube near the carrier. For most trucks and SUVs, you’ll find a broadcast code like “TUF G 001 1” or “6JH C 218 1” that breaks down into ratio, manufacturer, build date, and shift . The easiest method for modern Chevys is checking the glove box RPO sticker for G-codes like G80 (locking differential) and GU6 (3.42 ratio) . Classic passenger cars and vintage trucks use different code formats, so you’ll need the right reference chart for your model year . Physical inspection of the stamped code gives you the final answer—especially on older vehicles where the original axle may have been swapped.
Where to Find Your Rear Axle Identification
Chevrolet stamped axle identification codes in specific locations depending on the manufacturer. Here’s where to look:
Chevrolet-Produced Axles: The code is stamped on top of the right axle tube, outboard of the carrier . This is the most common location for trucks and SUVs.
Dana Axles: The code is stamped on the rear surface of the right axle tube . Some Dana units also displayed codes on a strip of tape attached to the outboard end of the axle tube.
Passenger Cars: Look for the code on the right front inboard side, about three inches outboard of the carrier . You might also find it on a metal tag attached to a cover bolt.
Front Axles: The identification tag is located near the axle tube .
Here’s the thing about axle codes—they’re often lightly stamped and can be hidden under years of grime. You might need to scrape off old paint and use a flashlight at an angle to read them.
Decoding the Stamped Code: What the Numbers Mean
Once you find the code, it follows a consistent pattern. Here’s what each part means:
Example Code: 6JH C 218 1
| Part | Meaning |
|---|---|
| 6JH | Axle ratio and ring gear size |
| C | Manufacturer (C = Chevrolet Buffalo, G = Chevrolet Gear and Axle, K = GM of Canada) |
| 218 | Julian date (218th day of the year) |
| 1 | Shift built (1 = first shift, 2 = second shift) |
Example Code: TUF G 001 1
| Part | Meaning |
|---|---|
| TUF | Axle ratio code |
| G | Manufacturer (G = Gear & Axle, C = Buffalo, K = GM of Canada) |
| 001 | Julian date (January 1) |
| 1 | Shift (1 = first shift) |
Classic Chevrolet Example: AB1031
| Part | Meaning |
|---|---|
| AB | Gear ratio code (for Buffalo plant—3.36 ratio) |
| 10 | Month (October) |
| 31 | Day of the month |
Common RPO Codes for Rear Axle Ratios
The easiest way to identify your rear axle ratio on modern Chevys is checking the glove box Service Parts Identification sticker. Look for G-codes that start with “G” :
| RPO Code | Description | Gear Ratio |
|---|---|---|
| G80 | Positraction Limited Slip Differential | — |
| GU2 | Rear Axle Ratio | 2.73 |
| GU4 | Rear Axle Ratio | 3.08 |
| GU5 | Rear Axle Ratio | 3.23 |
| GU6 | Rear Axle Ratio | 3.42 |
| GT4 | Rear Axle Ratio | 3.73 |
| GT5 | Rear Axle Ratio | 4.10 |
| GU8 | Rear Axle Ratio | 3.90 |
Important: G80 is the code for the locking differential itself. You’ll usually find it alongside a GU or GT code that tells you the ratio .
Passenger Car Axle Identification Codes
Chevrolet passenger cars use a different code system than trucks. Here are examples from 1984 models :
“F” Series (Camaro, Firebird)
| Code | Ratio | Ring Gear |
|---|---|---|
| 6ET | 3.08 | 7.5″ |
| 6JH | 3.23 | 7.5″ |
| 6JJ | 3.42 | 7.5″ |
| 6JK | 3.73 | 7.5″ |
| *6JZ | 3.23 | 7.5″ (Positraction) |
“G” Series (Full-size cars)
| Code | Ratio | Ring Gear |
|---|---|---|
| 2AH | 2.29 | 7.5″ |
| 2AJ | 2.41 | 7.5″ |
| 2AB | 2.73 | 7.5″ |
| 2AC | 3.08 | 7.5″ |
| 6AS | 3.42 | 7.5″ |
| 6TF | 3.73 | 8.5″ |
Heavy-Duty Truck Axle Ratios
For Chevy’s medium-duty trucks (Silverado 4500HD, 5500HD, 6500HD), the axle ratios determine maximum road speed :
| Rear Axle Ratio | Maximum Road Speed |
|---|---|
| 4.10 | 78 MPH |
| 4.30 | 75 MPH |
| 4.56 | 70 MPH |
| 4.88 | 65 MPH |
If you’re towing heavy loads, a numerically higher ratio (like 4.88) gives you better pulling power but lower top speed. For highway cruising, a lower ratio (like 3.42) means better fuel economy and higher speeds.
Common Stamped Codes by Manufacturer
Here’s a reference for interpreting the manufacturer letter in your axle code :
| Letter | Manufacturer |
|---|---|
| C | Chevrolet Buffalo |
| G | Chevrolet Gear and Axle |
| K | GM of Canada (McKinnon) |
| O | Oldsmobile |
| P | Pontiac |
Vintage Chevrolet Axle Codes (1940s)
For classic Chevys from the 1940s, the ratios were simpler :
| Model | Standard Ratio | Optional Ratio |
|---|---|---|
| Passenger | 4.11:1 | 3.73:1 |
| 1/2-Ton | 4.11:1 | — |
| 3/4-Ton | 4.55:1 | — |
| 1-1/2-Ton | 6.17:1 | 5.43:1 |
FAQ: Your Top Chevy Axle Questions Answered
Q: Where is the axle ratio code stamped on my Chevy truck?
A: Look on the top of the right axle tube, outboard of the carrier. Clean the area and use a flashlight at an angle to read the lightly stamped numbers .
Q: What does G80 mean on my RPO sticker?
A: G80 indicates your Chevy has the automatic locking rear differential (Positraction). It’s a limited-slip differential that provides better traction when one wheel starts spinning .
Q: How do I find my rear axle ratio without the RPO sticker?
A: Look for the stamped code on the right axle tube. The first three characters indicate the ratio and ring gear size .
Q: What gear ratio is best for towing?
A: Higher numerical ratios like 3.73 or 4.10 provide better pulling power for heavy loads. Lower ratios like 3.23 or 3.42 are better for fuel economy and highway cruising .
Q: Are all G80 differentials the same?
A: No. The G80 is a “Gov-Lock” differential that uses centrifugal force to lock the axles. It was used in many Chevy trucks, but the actual design varies depending on the axle size and model year .
Q: Can I change my rear axle ratio?
A: Yes, but it’s a major job requiring new ring and pinion gears, possibly a new carrier, and recalibration of the speedometer and shift points. GM offers approved ratio changes for some medium-duty trucks .
Q: What does the Julian date on the axle code mean?
A: The Julian date is the day of the year. For example, 218 means the 218th day (August 6 in a non-leap year). This helps identify the build date of the axle assembly .
References
Chevrolet Rear Axle Identification Resources:
