How to Identify your GM rear end gear ratio?


How can I Identify my GMC or Chevrolet rear end gear ratio?

Well.. this can be done by the General Motors "Regular Production Option" codes, also called... RPO Codes. The codes are provided by a tag labelled “Service Parts Identification” that's usually located inside the drivers door panel or glove box. 

These plates contain valuable information about your GM vehicle. Assuming that the rear end previously has not been swapped or modified, you can use these plates for accurate identification  of your rear end / differential.

The list below is a partial list of typical GM RPO Codes, specifically the codes pertaining to Axle Identification, Differential Type and Gear Ratio.

The prefix is usually F, G or H when referring to Axle Identification.
  
Code
Ratio Description
Ratio
FA0
Rear Axle
5.77:1
FA1
Rear 2 Speed  
4.88:1/6.94:1
FA2
Rear 2 Speed  
4.88:1/6.94:1
G44
Rear Axle       
3.07:1
G72
Rear Axle       
2.14:1
G75
Rear Axle       
3.70:1
G76
Rear Axle / Posi / Limited Slip
3.36:1
G80
Rear Axle / Posi / Limited Slip
X
G81
Rear Axle / Posi / Limited Slip
X
G82
Rear Axle
4.56:1
G84
Rear Axle
4.10:1
G86
Rear Axle / Limited Slip
X
G87
Ring Gear
8.5"
G89
Ring Gear,
7.5"
G90
Rear Axle
3.15:1
G91
Rear Axle / Special Highway
3.08:1
G92
Rear Axle
3.08:1
G94
Rear Axle
3.31:1
G96
Rear Axle
3.55:1
G97
Rear Axle
2.37:1
GH0
Rear Axle
3.54:1
GH2
Rear Axle
2.29:1
GH3
Rear Axle
2.77:1
GH4
Rear Axle
2.92:1
GH7
Rear Axle
2.73:1
GJ1
Rear Axle
5.38:1
GJ2
Rear Axle
5.13:1
GK7
Rear Axle
4.78:1
GK8
Rear Axle
4.33:1
GK9
Rear Axle
4.63:1
GL0
Rear Axle
5.13:1
GL3
Rear Axle
6.17:1
GM1
Rear Axle
2.59:1
GM2
Rear Axle
3.44:1
GM3
Rear Axle
3.45:1
GM4
Rear Axle
3.67:1
GM5
Rear Axle
3.89:1
GM6
Rear Axle
4.22:1
GM7
Rear Axle
3.68:1
GM8
Rear Axle
2.56:1
GN9
Rear Axle
4.11:1
GS1
Rear Axle
2.73:1
GS3
Rear Axle
3.73:1
GS4
Rear Axle
3.70:1
GS5
Rear Axle
4.11:1
GS6
Rear Axle
4.56:1
GS8
Rear Axle
3.94:1
GT1
Rear Axle
2.56:1
GT2
Rear Axle
2.29:1
GT4
Rear Axle (Dup of 5X1)
3.73:1
GT5
Rear Axle (Dup of GT8)
4.10:1
GT7
Rear Axle
3.33:1
GT8
Rear Axle (Dup of GT5)
4.10:1
GU1
Rear Axle
2.41:1
GU2
Rear Axle
2.73:1
GU3
Rear Axle
2.93:1
GU4
Rear Axle
3.08:1
GU5
Rear Axle
3.23:1
GU6
Rear Axle
3.42:1
GU7
Rear Axle
2.77:1
GU8
Rear Axle
3.9:1
GU9
Rear Axle
3.91:1
GV0
Rear Axle
3.55:1
GV1
Rear Axle
2.73:1
GV2
Rear Axle
5.83:1
GV3
Rear Axle
3.08:1
GV4
Rear Axle
3.36:1
GV5
Rear Axle
3.55:1
GV7
Rear Axle
4.11:1
GV8
Rear Axle
2.72:1
GV9
Rear Axle
4.25:1
GW2
Rear Axle
2.56:1
GW3
Rear Axle
2.56:1
GW4
Rear Axle
3.31:1
GW5
Rear Axle
2.73:1
GW6
Rear Axle
3.27:1
GW8
Rear Axle
4.10:1
GW9
Rear Axle (Dup of GU3)
2.93:1
GX1
Rear Axle
3.70:1
GX2
Rear Axle
3.07:1
GX4
Rear Axle
3.75:1
GX5
Rear Axle
4.09:1
GX6
Rear Axle
3.53:1
GY2
Rear Axle
3.31:1
GY4
Rear Axle
4.53:1
GY5
Front Axle
3.65:1
GY9
Rear Axle
4.31:1
H01
Rear Axle
3.07:1
H04
Rear Axle / Single Speed
4.11:1
H05
Rear Axle
3.73:1
H12
Rear Axle / Single Speed
21000 Lbs
H42
Rear Axle
6.17:1
H43
Rear Axle
5.43:1
HA3
Rear Axle / Single Speed
5.29:1
HC4
Rear Axle
4.56:1
HC7
Rear Axle /  Single Speed
2.38:1
HC8
Rear Axle /  Single Speed
3.21:1
HC9
Rear Axle
5.13:1
HE3
Rear Axle / Single Speed
3.07:1
HE4
Rear Axle
3.40:1
HF7
Rear Axle /  Dana 70 /Single
4.56:1
HF8
Rear Axle
4.88:1
HJ1
Rear Axle
4.55:1
HJ2
Rear Axle
5.86:1
HJ3
Rear Axle
4.75:1
HJ4
Rear Axle
6.50:1
HJ5
Rear Axle
5.57:1
HJ6
Rear Axle
4.78:1
HJ7
Rear Axle
4.88:1
HK1
Rear Axle
2.87:1
HK3
Rear Axle
6.14:1
HK9
Rear Axle / Single Speed
5.86:1
HO4
Rear Axle
4.11:1
HO6
Rear Axle
4.63:1
247
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