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Home arrow Rear End & Differential Ring Gear and Pinion Sets arrow What gear ratio do I have in my GM or Chevrolet



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What gear ratio do I have in my GM or Chevrolet rear end, do I have positraction Print E-mail

How do I find my rear differential ratio?

Here we present information to assist you in the  determination of what rear end ratio you have in your General Motors differential. In the second table you will be able with your RPO code to locate and determine just what rear differential ratio your What rear end ratio do I have in my Chevy General Motors vehicle left the factory with.  General Motor rear end differentials are referred to by the diameter of the ring gear, i.e. 8.5 inch, 10.5 inch.  Links are provided in the first table set identifying the different rear end types, see table.  Using these tables you will be able to locate the detailed information on replacement parts, upgrades and changing ratio parts and accessories for improving the performance of your vehicles differential. For front wheel drive General Motors ring and pinion replacements please give us a call 800-216-1632.

How does switching your rear end ration help the driver or vehicle performance?

We specialize in matching your tires and axles with the desired differential ratio's, we have a wide variety of gear sets in stock and can recommend and select the best suited differential for your driving application. We will recommend the right gear ratio to match your engine horsepower, transmission specifications and tires that you may have selected. 

Thinking about changing tire size we can help, consult our Look up chart for determination of engine RPM, gear ratio and tire size combination. Larger tires on lifted truck suffer from loss of power, changing the ring gear and pinion to a lower ratio is the answer.  Changing rear end ratio can improve fuel mileage, reduce and extend engine life, and/or add additional power for your towing requirements.

Why you need a positraction?

A positraction unit, when your vehicle is negotiating a corner, the outside wheel has to travel a grater distance than the inside wheel. Therefore, the outside wheel must turn faster than the inside wheel. The differential is the device within the axle assembly which, in addition to transmitting the power to each axle shaft/wheel, allows one wheel to turn at a different speed than the other.  Without positraction only one rear wheel receives the power.  In bad road conditions say, mud, ice or snow traction to one wheel is bound to get you stuck.  Installing a positraction provide power to both wheels at the same time, a significant improvement in traction.

General Motors Production Options. The following Regular Production Option (RPO) codes identify the rear axle and transaxle overall final drive gear Ratios. These codes can be located on the RPO sticker in the glove box or in the trunk on most GM vehicles.  Axle codes typically begin with the letter  F, G and H.  RPO Codes G80,, G81m and G86 indicated that the differential left the factory with a positraction.  For positraction replacements and parts see the following link.  Positraction units are available for many General Motor FWD Front Wheel Drive models.

A chart is also provided which presents Differential cover/cover gasket shapes, a common technique to identify differential ring gear diameter.  And a Dana/Spicer Parts illustration showing how to locate the Dana bill of material number is provided. This is a critical number to ensure that you find correct parts the first time.  For example Dana used in some cases 3 to 4 different ring gear widths for say a Dana 35 ring gear, so the set up is not the same for each gear category.


Find General Motors Differential Parts and Accessories at the following links:

Differential Name/Description
 Application  
GM 7.5" Rear End Parts & Accessories
 Model  Year
GM Passenger Car (Except H body Monza, Vega, Starfaire)

77-93

Camaro, Z28

82-97

Chevrolet S-10 & S-15

77-97

Pontiac Firebird & Trans Am

82-97

 
GM 8.2" (non-BPO) Rear End Parts & Accessories
Model Year
Chevrolet 65-70
Chevelle 64-72
Chevy II 64-70.5
Camaro 67-70
Nova 70-72
 
GM 8.5" 10 Bolt Rear End Parts & Accessories
Model Year Model

Year

Chevrolet 70-76 Trans-AM

72-81

Chevelle 70-76 C10, K10 & K20 Front

77-87

Chevy II 70-75 Blazer Front

77-91

Camaro 70-81 C10, K10 & Blazer

80-94

GTO/Firebird 70-81 K1500 Front IFS 88 & Up
Olds F-85 70-76 K2500 Front IFS 88 & Up
Z-28 72-81  
chevytrk_large.jpg
 GM 8.875" 12 Bolt Car Rear End Parts & Accessories  
Model Year   Model

Year

Chevrolet 65-72   Firebird

GTO

70-72

Chevy II 65-72   Nova

70-72

Chevelle 65-72   Olds F85

68-69

Camaro 67-72  


 
 
Model Year
G20, G25 64-82
G10, G15 64-81
K10, K15, C10, C15 64-82
 
 chevylogo_large.jpg
gmclogo_large.jpg
GM 9.5" 14 Bolt Rear End Parts & Accessories
Model Year Model

Year

C10, C15, C20 88-96 K30-K35

89-96

C30, C35 83-96 3/4 - 1 ton

81-92

K10, K15 88-96 3/4 - 1 ton Front IFS

88-96

K20, K25 81-96  
 
GM 10.5" Rear End Parts & Accessories

Model Year Model

Year

3/4 Ton 1 Ton 73-92 K20, K25

73-96

G30, G35 73-96 K30, K35

73-96

C20, C25 73-96  

 

C30, C35 73-96  

 


 

GM 11.5" Rear End Parts & Accessories
Model

Year

C/K Truck

2001-UP

G Van, P-Truck

2001-UP

1 Ton All

2001-UP

 

The most accurate method of determining a rear axle gear ratio is to look in the vehicle manufacturer's service manual.  The following Regular Production Option (RPO) codes identify the rear axle and trans axle overall final drive gear ratio's. These codes can be located on the RPO sticker in the glove box or in the trunk on most GM vehicles. These codes are arranged in alphanumeric order. Please refer to the information below
 
RPO CODE DESCRIPTION
RATIO
F16 TransAxle Final Drive
2.53
F17 TransAxle Final Drive
2.84
F18 TransAxle Final Drive
2.65
F25 TransAxle Final Drive
3.32
F29 TransAxle Final Drive
2.82
F36 Axle Front
2.19
F45 Axle Front
2.93
F47 Axle Front
2.73
F57 Axle Front
3.15
F62 TransAxle Final Drive
2.39
F67 TransAxle Final Drive
3.19
F68 TransAxle Final Drive
3.45
F75 TransAxle Final Drive
3.18
F77 TransAxle Final Drive
3.73
F79 TransAxle Final Drive
2.97
F82 TransAxle Final Drive
3.23
F83 TransAxle Final Drive
3.05
F90 Axle Front
2.73
FA0 Rear
5.77
FA1 Rear 2 SPEED
4.88/6.94
FA2 Rear 2 SPEED
4.88/6.94
FH5 TransAxle Final Drive
2.81
FH6 Axle Front
3.64
FH7 TransAxle Final Drive
4.12
FH8 Axle Front
2.40
FH9 TransAxle Final Drive
2.60
FJ1 Axle Front
4.18
FJ2 Axle Front
3.74
FJ3 TransAxle Final Drive
3.35
FJ4 Axle Front
4.53
FJ5 Axle Front
4.19
FJ7 Axle Front
4.56
FP0 TransAxle Final Drive
2.55
FP1 TransAxle Final Drive
2.72
FP2 TransAxle Final Drive
3.58
FP3 TransAxle Final Drive
2.73
FP4 TransAxle Final Drive
2.69
FP5 TransAxle Final Drive
2.95
FP6 TransAxle Final Drive
3.54
FP7 TransAxle Final Drive
3.73
FP8 TransAxle Final Drive
3.54
FP9 TransAxle Final Drive
3.54
FQ2 TransAxle Final Drive
3.48
FQ3 TransAxle Final Drive
2.86
FQ4 TransAxle Final Drive
3.57
FQ6 TransAxle Final Drive
4.12
FQ8 TransAxle Final Drive
2.96
FQ9 TransAxle Final Drive
3.21
FR2 TransAxle Final Drive
2.93
FR3 TransAxle Final Drive
3.69
FR6 TransAxle Final Drive
3.84
FR7 TransAxle Final Drive
3.95
FR8 Axle Front
4.17
FR9 TransAxle Final Drive
3.29
FV0 TransAxle Final Drive
3.67
FV1 TransAxle Final Drive
3.72
FV2 TransAxle Final Drive
4.18
FV3 TransAxle Final Drive
3.11
FV4 TransAxle Final Drive
3.71
FV5 TransAxle Final Drive
4.19
FV6 TransAxle Final Drive
4.24
FV7 TransAxle Final Drive
4.29
FV8 TransAxle Final Drive
4.31
FV9 TransAxle Final Drive
4.53
FVO TransAxle Final Drive
3.67
FW2 TransAxle Final Drive
3.06
FW3 TransAxle Final Drive
4.02
FW4 TransAxle Final Drive
3.89
FW5 TransAxle Final Drive
4.10
FW6 TransAxle Final Drive
3.42
FW7 TransAxle Final Drive
3.83
FW8 TransAxle Final Drive
4.28
FW9 TransAxle Final Drive
3.43
FWS TransAxle Final Drive
4.10
FX1 TransAxle Final Drive
3.94
FX2 TransAxle Final Drive
2.66
FX4 TransAxle Final Drive
3.35
FX8 TransAxle Final Drive
3.61
FY1 TransAxle Final Drive
2.36
FY3 TransAxle Final Drive
3.79
FY5 TransAxle Final Drive
3 52
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, 8.50 Inch

G89 Ring Gear, 7.50 Inch

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 WITH 5 X 1)
3.73
GT5 Axle Rear (DUP WITH GT8)
4.10
GT7 Axle Rear
3.33
GT8 Axle Rear (DUP WITH 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 WITH 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
5.13
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 SPEED
5.86
HO4 Axle Rear
4.11
HO6 Axle Rear
4.63


The following figure presents differential cover/cover gasket shapes. Counting cover bolts and cover shapes is a common method to determine which ring gear diameter differential you have in your Rear wheel drive vehicles. See following paragraph for selection of correct Dana parts.

gmdanadiffgaskets_large.jpg

 

 

 

 

 

 

 

 

 

 

 

When ordering Dana/Spicer Differential Parts provide bill of material number. This number is stamped on your right hand side axle tube. It's a number like 603XX-X, 604XX-X or 605XX-X. With this number you can tell exactly what components the factory used in the assembly of your differential. 

billofmaterial_large.jpg

 

 
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