Rearend identification

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[edit] Introduction

There are several ways to tell what the type/size/application of a rearend. Besides visually checking and comparing rearends to one another, there are casting numbers, build codes and dates displayed or cast/stamped in various locations on the rearend and elsewhere. These all can be used to help ID a rearend.

[edit] Casting numbers

Many if not all rear end housings will have some sort of casting number or ID cues to identify it. If the RPO decal is present (newer vehicles) or the broadcast or "build" sheet is available, it can show what was originally in the vehicle. Sometimes body/fender/cowl tags contain coded info that may list specifics on the rearend.

[edit] Axle codes

Example of GM stamped axle code
GM axles are stamped on the axle tube (and sometimes the center section) with codes for the year and ratio. Sometimes the casting numbers can also be used to show whether an axle housing is a limited slip differential (LSD) or not.

Some sites with ratio and axle code info are:

Ford rear ends sometimes had tags under one of the carrier bolts that had the ratio and a code for being a LSD or not. Ford also used an axle code on the body tag on some models.

[edit] Date codes

The date code format can vary, but sometimes the date code is a letter followed by two or three numbers. The letter is the month. The next number or two numbers will be the day of the month. The last number is the last digit of the year.

Example: C124
  • C = March (A = Jan., B = Feb., etc.)
  • 12 = day of the month
  • 4 = year ending in 4, i.e. 1964, 1974, 1984, etc.

[edit] Axle dimensions

[edit] Axle flange dimensions

Axle flange dimensions from Moparinterests

[edit] GM removable carrier type

The removable carrier rear end was used by GM for a number of years in passenger cars before GM started using the integral carrier rear end. The Pontiac/Olds versions from the later '50s were a drag racing mainstay for many years- even in front engined Top Fuel dragsters and Altereds.

[edit] 1955-'64 carrier casting numbers

3 series (2.73:1- up): 410408N

2 series (2.56:1- down):410409N The Chevy version used various tags to designate the ratio.


[edit] Casting numbers and casting codes

  • The casting number for a 1956 case should be 3707306
  • The casting number for a 1957-'61 non-posi center case should be 3725899
  • The casting number for a 1957-'61 posi center case is 3743833
  • The casting number for a 1962-'64 posi center case is 3789812

The above are all casting numbers for passenger cars. These casting numbers are the same for Corvette rearends because the rearends were cast and assembled at just two facilities: the Detroit Gear and Axle plant and the Buffalo, NY plant. The only thing that would be different between the same year Corvette and a passenger car rearend center section would be the stamped (not cast) two letter code on the passenger side of the case. The code designates the gear ratio.

[edit] Ford

Ford used a vast array of rear ends over the years. Besides the codes stamped into the axle tubes, some carried ratio and/or posi tags as well as the vehicle having a plate containing coded info on the rearend. Below are photos of some of the more common rear ends for visual reference and comparison:

[edit] Removable carrier

Removable carrier, rear view.

[edit] ID

An easy way to tell the difference between the 8-inch and the 9-inch Ford differential is that on an 8-inch, a socket will fit on the lower nuts seen in this picture. Since the pinion centerline is lower on a 9-inch, a wrench is needed to gain clearance.

[edit] 8 inch

8 inch Ford front view
8 inch Ford differential details. Note the accessibility of the bottom bolts indicating it's not a 9 inch.

[edit] 9 inch

One of the strongest Ford rear end was the 9". Still one of the best rearends to modify or use in stock form to handle big horsepower.

9 inch Ford rearend

[edit] 9-3/8 inch

Removable carrier. Found in some Lincoln, Mercury and Thunderbird.

[edit] Non-removable carrier (Salisbury-style rearend)

[edit] 8.8 inch

8.8" rear end in a Ford F150 4X4
8.8" rear end with damper weight attached

[edit] 8.7 inch

Non-removable carrier. Found in Granada, Monarch 1977 to 1978.

8.7 inch Ford rear end

[edit] 7.75 inch

Non-removable carrier. Found in Fairlane.

[edit] 7.5 inch

Non-removable carrier. Found in light duty applications such as six cylinder Falcon, Fairlane and 170 cid Maverick (Mavericks powered by 200 cid, 250 cid and 302 cid engines had the 8-inch differential).

[edit] 7.25 inch

Non-removable carrier. Found in Falcon, Econoline, Fairlane, Comet.

[edit] 7 inch

Non-removable carrier. Found in Falcon.

[edit] 6.75 inch

Non-removable carrier. Found in some Pinto and Mustang II.


[edit] Columbia 2-speed rear end

More of an overdrive unit than an actual rear end. Included in the Ford section since it was offered as an option on '30s to '40s Fords.

[edit] General Motors

[edit] GM diff covers

GM diff covers

GM 10bolt id.jpg

10 bolt 8.5 inch GM corporate rear end

[edit] 10 bolt

[edit] 10 bolt ID tips

If you don't have the codes on hand to identify if a 10 bolt rear end is an 8.5" or not, you can measure the distance between the very bottom bolt for the cover and the next adjacent bolt (either right of left), it will be 3-3/4" for a 8.5" and 3-1/4" for a 7.5".
Warning Note: Some installation kits for the 8.5" and 7.5" use ring gear bolts with a 5/8" head, so if someone has rebuilt the rearend with one of these kits the bolts will have smaller heads than the original bolts.

Another tip is to check the size of the pinion nut. The 8.2" uses a 1-1/8 inch socket on the nut and the 7.5" and 8.5" use a 1-1/4 inch socket. That is as long as they have a OEM type nut on them.

There are usually two distinctive lugs cast into the bottom of the 10 bolt rear end housing. These lugs are arrowed in the image above.

The ring gear of the corporate 10 bolt is secured by 7/16-20 left hand thread bolts having a 3/4" hex head on them; there will be ten bolts holding the ring gear to the differential. The ring gear is (as mentioned) 8.5" diameter and the pinion shaft diameter is the same as the 12 bolt at 1.625". The 8.5" pinion has 30 splines.

The 8.2" diff will have 10 bolts holding the ring gear on the diff, the bolts will have a 9/16" hex head and be right hand threaded. The 8.2" uses ten 3/8-24 right hand thread bolts to hold the ring gear on the diff. The pinion diameter is 1.438", having 25 splines.

The 7.5" diff will have the ring gear secured with 10 bolts that are 7/16-20 LH thread, like the 8.5" corporate rear end. However, the ring gear diameter is smaller than the 8.5" differential.

[edit] 8.75 inch 10-bolt

This rearend was used in some mid-'70s Chevrolet station wagons, Impala, Caprice, some Chevelles, El Caminos, usually with larger engines and/or heavy duty options (towing, etc.). Also possibly found in some Pontiac LeMans, some 1977 Buick Regals and Cadillac models (needs confirmation).

Can be found with either 28 or 31 spline axles. It has a 10-bolt cover with indentions next to the axle tubes and 12 bolts holding the ring gear to the carrier (the bolts have a 3/4" hex head, right hand threads). The pinion nut is 1-1/4", it has 3" axle tubes.

This is a strong rearend, but unfortunately it was only used briefly and aftermarket support is poor.

GM 8.75" 10-bolt rear cover

[edit] 8.5 inch 10-bolt

Sometimes referred to as the "corporate 10-bolt", the GM 8.5" 10-bolt rearend began production in 1971 to replace the 8.2" and 12-bolt rearends. There was simultaneous use of the 8.2" and 8.5" rearends during the changeover period, like in the Nova. Has a 10 bolt cover as well as 10 bolts securing the ring gear. Ring gear bolts are 7/16 - 20 LH threads (also shared with the 7.5/7.625").

The 8.5" 10-bolt GM rearend has a 30 spline pinion, uses C-clips, and could have 28 or 30 spline axles depending on the year (30 spline axles were used after 1988). 4 wheel drive 8.5" front differentials manufactured between 1977-91 share the same differential gears, bearings, and pinion seals but has a modified housing and cover which has an indentation to clear suspension travel. It uses a 1-1/4" pinion nut. Ring gear diameter was increased to 8.6" when used with the GMT800 platform light duty trucks (1999-06 Silverado/Sierra).

Apollo:  1973 - 1975   Bel Air:  1970 - 1975  
Blazer:  1979 - 1994   Bonneville:  1970 - 1986  
C10 1/2 Ton (2WD):  1979 - 1987   C15/ C1500 1/2 Ton (2WD):  1979 - present  
C1500 1/2 Ton (2WD):  1988 - 1998 (incl. GMT400-based Blazer (92-94), Tahoe/Yukon, Escalade, Denali, 1/2 ton Suburban)   Camaro:  1970 - 1981  
Caprice:  1970 - 1996 (includes '94-'96 Impala SS and 9C1 police package)   Catalina:  1970 - 1981  
Chevelle/Malibu:  1973 - 1973   Cutlass:  1970 - 1977  
Cutlass:  1985 - 1987 (442 package)   El Camino:  1971 - 1976  
Electra:  1971 - 1989   Firebird:  1970 - 1981  
G10 1/2 Ton:  1979 - 1989   G15/ G1500 1/2 Ton:  1979 - 1988  
G20 3/4 Ton:  1975 - 1989   G25/ G2500 3/4 Ton:  1978 - 1988  
Grand Prix:  1971 - 1987   GTO:  1970 - 1977  
Impala/Caprice:  1971 - 1996 ('77-'96 B, C, and D platform for station wagons, diesels, 9C6 (taxicab) and 9C1 police package   K10/ K1500 1/2 Ton (4WD):  1979 - present  
K15/ K1500 1/2 Ton (4WD):  1979 - present   K5 Blazer (4WD):  1979 - 1991 (1979-'82 are overlap years - also applicable to C/K 10 series incl. Suburban  
LeMans:  1971 - 1983   Malibu:  1973 - 1983  
Monte Carlo:  1973 - 1978   Nova:  1970 - 1979  
Omega:  1973 - 1979   Phoenix:  1978 - 1979  
Regal:  1973 - 1987   Regal:  1985 - 1987  
Riviera:  1975 - 1978   Skylark:  1970 - 1972  
Skylark:  1975 - 1979   S10,Sonoma:  1995 - 2003 (4WD with ZR2 option, S10 SS, Xtreme, and 4.3L trucks with a manual transmission option  
Suburban 1/2 Ton:  1979 - 1991   Suburban 1/2 Ton:  1979 - 1991  
Suburban 1/2 Ton:  1979 - 1991   Suburban 1/2 Ton:  1979 - 1991  
Trans Am:  1970 - 1981   Ventura:  1976 - 1977  

[edit] 8.2 inch 10-bolt

The 8.2" rearend was used through 1970 in the B-body (Impala) and F-body (Camaro) cars. The 8.2" was used through 1971 in the X-body (Nova) and through 1972 in the A-body (Chevelle).

Bel Air:  1964 - 1972   Biscayne:  1964 - 1972  
Camaro:  1967 - 1970   Caprice:  1965 - 1971  
Chevelle/ Malibu:  1964 - 1972   Chevy II:  1964 - 1968  
El Camino:  1964 - 1972   Impala:  1964 - 1972  
Monte Carlo:  1970 - 1972   Nomad:  1968 - 1972  
Nova:  1964 - 1972   Skylark:  1964 - 1969  
Tempest:  1964 - 1970   Trans Am:  1969 - 1972  
Ventura:  1971 - 1971   Wildcat:  1964 - 1972  

[edit] 10 bolt carriers

The corporate 10 bolt 8.5 inch rear end uses two different carrier series depending on the rear gear ratio:

  • 2.56 and higher gears ("higher" gears have lower numbers, like 2.41, 2.29, etc.) go on the 2 series carrier
  • 2.73 and lower ("lower" gears = higher numbers, like 3.08, 3.23, etc.) go on the 3 series carrier

A 3-series gear can be installed on a 2-series carrier by using a ring gear spacer, but this is not advised for stick shift applications, or if there's a lot of traction, HP and/or weight involved.

Mr. Gasket p/n 908A ring gear spacer for the 8.5" GM 10-bolt 2-series carrier

[edit] 8.5" non C-clip rearend

The non C-clip differential share the same ring/pinion (incl. pinion bearings, differential carrier) with the C clip version but has pressed on axle bearings similar to a Dana 44 or Ford 9 inch. Differential cover looks similar to the BOP 8.2 10 bolt.

The 1971-'72 Buick GS/Skylark and Olds Cutlass A-body 8.5 10 bolt did not have C-clip axles.

The non C-clip 8.5" 10 bolt, type "C" rearend was used in some 1969-'72 Pontiac GP and 1970-'72 Monte Carlo.

There have been non C-clip rearends found in Chevelle wagons, and some El Caminos through at least 1974.

[edit] 12-bolt cover/10-bolt ring gear

This "O" (Olds) rearend was used in the Olds Cutlass A-body from 1968-'70. It was the rearend that had a 12 bolt cover, but with a 10 bolt 8.5" ring gear. This is not the same as the corporate 8.5 rearend, and there is no parts interchange between the two rearends.

[edit] 12-bolt car

  • Ring gear diameter: 8.875"
  • Cover bolts: 12
  • Ring gear bolts: 12
  • Axle spline count: 30
  • Pinion spline count: 30
  • Carrier Breaks: 2.76-down / 3.07 / 3.90 / 4.10-up
  • Pinion Nut Size: 1-1/8"

Pinion yokes interchange between the 12-bolt car and truck. Originally the 12-bolt rearend used U-joint sizes 1310, 1330 or GM 3R series.

Bel Air:  1964 - 1972  (Rear) Biscayne:  1964 - 1972  (Rear)
Camaro:  1967 - 1972  (Rear) Caprice:  1966 - 1970  (Rear)
Chevelle/ Malibu:  1964 - 1972  (Rear) Chevy II:  1964 - 1968  (Rear)
El Camino:  1965 - 1972  (Rear) GTO:  1970 - 1972  (Rear)
Impala:  1964 - 1972  (Rear) Monte Carlo:  1970 - 1972  (Rear)
Nomad:  1968 - 1972  (Rear) Nova:  1964 - 1972  (Rear)
Trans Am:  1969 - 1972  (Rear) Wildcat:  1964 - 1972  (Rear)

[edit] U-joints

  • 1310 series, (aka "small Chevy") has 1.063" diameter caps, 3.219" measured across to lock ring points (1-1/16" x 3-7/32"), uses outside clips. Was OEM for many 1967-74 GM cars. Also used with Ford F100s (including early F150s prior to 1980), Broncos, Econolines with 9 inch differentials and AMC/Jeep products (pinion to driveshaft location - driveshaft to transmission yoke used a hybrid U-joint with outside and inside clips)

Warning Note: There's also a 1310 "special" U-joint, which has two 1-1/16" and two 1-1/8" caps. Used OE on some Fords and available from the aftermarket as an adapter U-joint.

  • 1330 series pinion yokes use locating tabs to center the U-joint, has 1.063" diameter caps, 3.625" measured across to lock ring points (1-1/16" x 3-5/8"), uses outside clips. Used on heavy-duty/high performance/big engine applications.
  • GM 3R series is the "inside C-clip", or "inside lock" style. Used ~1975-up. It does not use locating tabs. It has 1.125" diameter caps, 2.5625" measured across caps (1-1/8" x 2-9/16"), aftermarket/replacement U-joints uses inside clips, originals use plastic injection.

On the 12-bolt, the hardware used to hold the U-joint into the pinion yoke was either two 5/16" U-bolts, or 4 bolts and 2 metal straps. Both styles were used on original equipment applications. The U-bolts are the preferred method, if for no other reason than if either were to fail the U-bolt type can be easily replaced while the strap type might break off the bolt inside the yoke, making extraction difficult.

U-jnt girdle.jpg

The yokes may be different for straps or U-bolts. The strap yoke (if smaller) can be drilled out to use U-bolts, but in some cases this leaves too little metal around the holes. A better approach is to use a yoke made for U-bolts in the first place.

U-joint girdles (right) can be used to replace the original hardware. Be sure to match the diameter of the fasteners to the hole size of the yoke.

[edit] MOPAR

Dana diff tags
Dana diff covers

[edit] AMC

[edit] ID

AMC axle codes are stamped on the differential casting between the cover and the tube weld hole on the passenger side) beginning in 1970 for the AMC 20 series rearend, 1972 for the AMC 15 series. First four letters/ratios are 1970 rear axle codes stamped on the differential housing cover flange at about 3 o'clock:

A = 3.54:1 B = 3.15:1 C = 2.87:1 D = 3.91:1 E = 3.58 (12/43) F = 3.08 (13/40) G = 3.31 (13/43) H = 2.73 (15/41) J = 2.37 (19/45)

The 15 series had 10 bolt oval cover with drain plug center right.

[edit] 15 series rearend

The AMC 15 series rearend has a 7-9/16" ring gear. It was used in 1965 and earlier models with 196 ci or 199 ci inline 6 engines. The small cars (cars other than those listed below as "big car") used the AMC 15 rearend with inline 6 engines, AMC 20 rearend was used with V8 engines. The AMC 20 rearend could be ordered in fleet cars with inline 6 engines. AMC sold the tooling equipment for its differentials to the Dana Corporation in 1985. The AMC 15 was modified by Dana and rebranded as the Dana 35/35C. Ring/pinion sets including the axleshafts do not interchange with the AMC 15.

[edit] 20 series rearend

The big cars (Ambassador, Classic, Rebel, Matador and Marlin) used the AMC 20 rearend with 232 ci inline 6 and bigger engines.

The series 20 was used in Jeeps as well as AMC passenger cars. A Jeep 20 series rearend would have a 5 on 5" wheel bolt pattern. Passenger cars used the 5 on 4-1/2" wheel bolt pattern.

20 series under a 1966 Rouge

[edit] GM RPO axle codes

G80 Axle Positraction, Limited Slip

G81 Positraction Rear Axle

G82 Axle Rear


G84 Axle Rear


G86 Axle , Rear, Limited Slip

G87 Ring Gear, 8.50 Inch

G89 Ring Gear, 7.50 Inch

G90 Rear


G91 Special Highway Rear Axle


G94 Axle Rear


G96 Axle Rear


G97 Axle Rear


GH0 Axle Rear


GH2 Axle Rear


GH3 Axle Rear


GH4 Axle Rear (2LS V6 Camaro)


GH7 Axle Rear


GJ1 Axle Rear


GJ2 Axle Rear


GK7 Axle Rear


GK8 Axle Rear


GK9 Axle Rear


GL0 Axle Rear


GL3 Axle Rear


GM1 Axle Rear


GM2 Axle Rear


GM3 Axle Rear


GM4 Axle Rear


GM5 Axle Rear


GM6 Axle Rear


GM7 Axle Rear


GM8 Axle Rear


GN9 Axle Rear


GS1 Axle Rear


GS3 Axle Rear


GS4 Axle Rear


GS5 Axle Rear


GS6 Axle Rear


GS8 Axle Rear


GT1 Axle Rear


GT2 Axle Rear


GT4 Axle Rear (DUP WITH 5 X 1)


GT5 Axle Rear (DUP WITH GT8)


GT7 Axle Rear


GT8 Axle Rear (DUP WITH GT5)


GU1 Axle Rear


GU2 Axle Rear


GU3 Axle Rear


GU4 Axle Rear


GU5 Axle Rear


GU6 Axle Rear


GU7 Axle Rear


GU8 Axle Rear


GU9 Axle Rear


GV0 Axle Rear


GV1 Axle Rear


GV2 Axle Rear


GV3 Axle Rear


GV4 Axle Rear


GV5 Axle Rear


GV7 Axle Rear


GV8 Axle Rear


GV9 Axle Rear


GW2 Axle Rear


GW3 Axle Rear


GW4 Axle Rear


GW5 Axle Rear


GW6 Axle Rear


GW8 Axle Rear


GW9 Axle Rear (DUP WITH GU3)


GX1 Axle Rear


GX2 Axle Rear


GX3 TransAxle Final Drive


GX4 Axle Rear


GX5 Axle Rear


GX6 Axle Rear


GX8 TransAxle Final Drive


GY2 Axle Rear


GY3 TransAxle Final Drive


GY4 Axle Rear


GY5 Axle Front


GY7 TransAxle Final Drive


GY9 Axle Rear


[edit] GM ratio to tooth count

Axle Ratio Tooth Combination

[edit] Resources

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