Accurate Differential Identification is a very important step in your 5 or 6-speed upgrade project.
The following information is provided to help you identify the differential you are working on.
If in doubt, consult one of our differential experts at 208-453-9800!
Professional technical support is available Monday thru Friday from 8am to 5pm Mountain Time.
Differential Identification by Tag Number
Ford Differential Tags
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Ford differential tags are very straightforward, as indicated above. The Month of Manufacture uses the following format:
A = January, B = February, C = March, etc.
GM RPO Codes – Factory Identification Labels and Interpretation
GM RPO Codes or General Motors’ “Regular Production Option” codes contain lots of valuable information about your GM vehicle. Identify your GMC or Chevrolet rear end gear ratio by the RPO Codes, usually located on the placard labeled “Service Parts Identification” inside the driver’s door panel or glove box. (Accurate identification using the GM RPO code assumes that the rear end has not been previously modified) The prefix is usually F, G or H when referring to Axle Identification. The list below is a partial list of typical GM RPO Codes, specifically the codes pertaining to Axle Identification, Differential Type, and Gear Ratio.
| RPO Code | Description | Ratio |
| G11 | Transaxle Final Drive | 2.56 |
| G44 | Axle Rear | 3.07 |
| G72 | Axle Rear | 2.14 |
| G75 | Axle Rear | 3.62 |
| G76 | Positraction Rear | |
| G80 | Axle Positraction, Limited Slip | |
| G81 | Positraction Rear Axle | |
| G82 | Axle Rear | 4.56 |
| G84 | Axle Rear | 4.10 |
| G86 | Axle Rear, Limited Slip | |
| G87 | Ring Gear, 8.5″ | |
| G89 | Ring Gear, 7.5″ | |
| G90 | Rear | 3.15 |
| G91 | Special Highway Rear Axle | 3.08 |
| G94 | Axle Rear | 3.31 |
| G96 | Axle Rear | 3.55 |
| G97 | Axle Rear | 2.73 |
| GH0 | Axle Rear | 3.54 |
| GH2 | Axle Rear | 2.29 |
| GH3 | Axle Rear | 2.77 |
| GH4 | Axle Rear | 2.92 |
| GH7 | Axle Rear | 2.73 |
| GJ1 | Axle Rear | 5.38 |
| GJ2 | Axle Rear | 5.13 |
| GK7 | Axle Rear | 4.78 |
| GK8 | Axle Rear | 4.33 |
| GK9 | Axle Rear | 4.63 |
| GL0 | Axle Rear | 5.13 |
| GL3 | Axle Rear | 6.17 |
| GM1 | Axle Rear | 2.59 |
| GM2 | Axle Rear | 3.44 |
| GM3 | Axle Rear | 3.45 |
| GM4 | Axle Rear | 3.67 |
| GM5 | Axle Rear | 3.89 |
| GM6 | Axle Rear | 4.22 |
| GM7 | Axle Rear | 3.68 |
| GM8 | Axle Rear | 2.56 |
| GN9 | Axle Rear | 4.11 |
| GS1 | Axle Rear | 2.73 |
| GS3 | Axle Rear | 3.73 |
| GS4 | Axle Rear | 3.70 |
| GS5 | Axle Rear | 4.11 |
| GS6 | Axle Rear | 4.56 |
| GS8 | Axle Rear | 3.94 |
| GT1 | Axle Rear | 2.56 |
| GT2 | Axle Rear | 2.29 |
| GT4 | Axle Rear (Dup of 5X1) | 3.73 |
| GT5 | Axle Rear (Dup of GT8) | 4.10 |
| GT7 | Axle Rear | 3.33 |
| GT8 | Axle Rear (Dup of GT5) | 4.10 |
| GU1 | Axle Rear | 2.41 |
| GU2 | Axle Rear | 2.73 |
| GU3 | Axle Rear | 2.93 |
| GU4 | Axle Rear | 3.08 |
| GU5 | Axle Rear | 3.23 |
| GU6 | Axle Rear | 3.42 |
| GU7 | Axle Rear | 2.77 |
| GU8 | Axle Rear | 3.90 |
| GU9 | Axle Rear | 3.91 |
| GV0 | Axle Rear | 3.55 |
| GV1 | Axle Rear | 2.73 |
| GV2 | Axle Rear | 5.83 |
| GV3 | Axle Rear | 3.08 |
| GV4 | Axle Rear | 3.36 |
| GV5 | Axle Rear | 3.55 |
| GV7 | Axle Rear | 4.11 |
| GV8 | Axle Rear | 2.72 |
| GV9 | Axle Rear | 4.25 |
| GW2 | Axle Rear | 2.56 |
| GW3 | Axle Rear | 2.56 |
| GW4 | Axle Rear | 3.31 |
| GW5 | Axle Rear | 2.73 |
| GW6 | Axle Rear | 3.27 |
| GW8 | Axle Rear | 4.10 |
| GW9 | Axle Rear (Dup of GU3) | 2.93 |
| GX1 | Axle Rear | 3.70 |
| GX2 | Axle Rear | 3.07 |
| GX3 | Transaxle Final Drive | 3.33 |
| GX4 | Axle Rear | 3.75 |
| GX5 | Axle Rear | 4.09 |
| GX6 | Axle Rear | 3.53 |
| GX8 | Transaxle Final Drive | 3.74 |
| GY2 | Axle Rear | 3.31 |
| GY3 | Transaxle Final Drive | 4.29 |
| GY4 | Axle Rear | 4.53 |
| GY5 | Axle Front | 3.65 |
| GY7 | Transaxle Final Drive | 4.18 |
| GY9 | Axle Rear | 4.31 |
| GYS | Transaxle Final Drive | 3.65 |
| H01 | Axle Rear | 3.07 |
| H04 | Axle Rear, Single Speed | 4.11 |
| H05 | Axle Rear | 3.73 |
| H12 | Axle Rear, 21000 Lbs, Eaton 21065S, Single Speed | |
| H42 | Axle Rear | 6.17 |
| H43 | Axle Rear | 5.43 |
| HA3 | Axle Rear, Single Speed | 5.29 |
| HC4 | Axle Rear | 4.56 |
| HC7 | Axle Rear, 7500 Lbs, Single Speed | 2.38 |
| HC8 | Axle Rear, Single Speed, Truck | 3.21 |
| HC9 | Axle Rear | 5.13 |
| HE3 | Axle Rear, 3500 Lbs, Single Speed | 3.07 |
| HE4 | Axle Rear | 3.40 |
| HF7 | Axle Rear, 10000 Lbs, Dana 70, Single | 4.56 |
| HF8 | Axle Rear | 4.88 |
| HJ1 | Axle Rear | 4.55 |
| HJ2 | Axle Rear | 5.86 |
| HJ3 | Axle Rear | 4.75 |
| HJ4 | Axle Rear | 6.50 |
| HJ5 | Axle Rear | 5.57 |
| HJ6 | Axle Rear | 4.78 |
| HJ7 | Axle Rear | 4.88 |
| HK1 | Axle Rear | 2.87 |
| HK3 | Axle Rear | 6.14 |
| HK9 | Axle Rear 10000 Lbs, Single Spd | 5.86 |
| HO4 | Axle Rear | 4.11 |
| HO6 | Axle Rear | 4.63 |
The most accurate differential identification is provided by the bottom line of the tag number or axle tube stamp. Differential tags can easily be used to identify Dana and Ford differentials.
Dana Spicer Differential Tags
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Dana Spicer B.O.M. Numbers
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The Bill of Material (BOM) number is used to identify Dana differentials. The BOM will identify the model number, the gear ratio, the type of differential, and all component parts. Traditional BOM’s are 6 digits followed by 1 or 2 digits and start with the numbers 60 or 61. On some tags, the first 2 digits don’t appear on the tag, but they must be used to identify the axle. For instance, you might see 5561-1 for the BOM, but the 60 has been dropped, and one would need to use 605561-1. Later BOM’s may start with the first 3 digits of 200, but these are typically not dropped from the tag.
The “Dana Expert” website is no longer available. However, the Dana Aftermarket Media Library can be used to identify all aspects of a particular axle using the Bill Of Materials number.
- Navigate to the Dana Aftermarket Media Library
- Enter the BOM number in the Keyword Search field (top left corner of the page).
- Click on the resulting literature link
- Search within the document by clicking on the Magnifying Glass at the top, or by simply using “Control-F” and re-entering the BOM number.