Here is a table that gives the codes for different rear axle ratio, differential type, manufacturer, and build date information. THe code is stamped on the right axle tube (as viewed from the front of the car) on the forward side. It’s tough to see when it’s still in the car. Of course some of the engine/tranny combinations listed were not available on the 78-83 Malibu. But this will aid you in finding a rearend to swap into your Malibu.
The first 3 digits indicate the axle code, the next one indicates manufacturer (B=Buick, O=Olds, C=Chevy, P=Pontiac), the next is Julian date it was built and the last it the shift it was made on. Limited slip rears had a tag on the differential cover that stated it needs posi fluid… that’s usually missing, if the cover has ever been off. However, a “B” in the axle code (i.e., 2BX) usually indicates a posi.
The 7.5″ rears have a differential cover that is smooth and kind of a squared off oval shape. The 8.5″ rears have a rounder shaped cover with a raisedhorizontal area in the middle.
1978
| Trans | Engine | Ratio | Peg Leg | Ltd Slip | Std/Opt |
| THM350 | 196 “C” 49 State | 2.73 | 2AB | 2BB | STD |
| THM350 | 231 “A” Cal 49 State | 2.73 | 2AB | 2BB | STD |
| THM350 | 231 “A” 49 State | 3.23 | 2AD | 2BD | OPT |
| THM350 | 231 “A” 49 State | 2.41 | 2AJ | 2BJ | OPT |
| THM350 | 231 “A” Hi Altitude | 3.23 | 2AD | 2BD | STD |
| THM350 | 231 “G” 49 State | 2.73 | 2AB | 2BB | STD |
| THM350 | 231 “3” 49 State | 2.73 | 2AB | 2BB | STD |
| Gear Ratio | Ring Gear | Assembly Codes |
| 2.41 | 7.5″ | AZ, BZ |
| 2.56 | 7.5″ | RY, SY, RC, SC, AA, BA |
| 2.73 | 7.5″ | AX, BX, RS, SX, RD, SD, AB, BB |
| 2.93 | 7.5″ | AG, BG |
| 3.23 | 7.5″ | RU, SU, AU, BU, RG, SG |
1979
| Trans | Engine | Ratio | Peg Leg | Ltd Slip | Std/Opt |
| THM350 | 3.8 (LD5) A | 2.41 | 2AJ | 2BJ | STD |
| THM350 | 3.8 (LD5) A | 2.73 | 2AB | 2BB | OPT |
| THM350 | 3.8 (LD5) A | 3.23 | 2AD | 2BD | OPT |
| THM350 | 3.8 (LD5) High Alt | 3.23 | 2AD | 2BD | STD |
| THM350 | 3.8 (LD5) A | 2.73 | 2RX | 2BX | STD |
| THM350 | 3.8 (LD5) A | 3.23 | 2AU | 2BU | OPT |
| THM350 | 3.8 (LD5) A Calif | 3.23 | 2AU | 2BU | OPT |
| THM350 | 3.8 (LC6) 2 Calif | 2.73 | 2AB | 2BB | STD |
| THM350 | 3.8 (LC6) 2 Calif | 2.73 | 2RX | 2BX | STD |
| THM350 | 3.8 (LC8) 3 | 2.41 | 2AJ | 2BJ | STD |
| THM350 | 3.8 (LC8) 3 | 2.73 | 2AB | 2BB | OPT |
| THM350 | 3.8 (LC8) 3 | 3.08 | 2AC | — | OPT |
| THM350 | 3.8 (LC8) 3 | 2.41 | 2AJ | 2BJ | STD |
| THM350 | 3.8 (LC8) 3 | 2.73 | 2AB | 2BB | OPT |
| THM350 | 3.8 (LC8) 3 Calif | 2.73 | 2AB | 2BB | STD |
| Gear Ratio | Ring Gear | Assembly Codes |
| 2.14 | 7.5″ | RH |
| 2.29 | 7.5″ | RA, AH, BH, AT, BT |
| 2.41 | 7.5″ | AJ, BJ, AZ, BZ |
| 2.56 | 7.5″ | RC, AA, BA, AY, BY |
| 2.73 | 7.5″ | AX, BX, RX, RD, AB, BB |
| 2.93 | 7.5″ | AG, BG |
| 3.08 | 7.5″ | AC, BC |
| 3.23 | 7.5″ | AD, BD, SC, RU, AU, BU, RG |
1980
| Trans | Engine | Ratio | Peg Leg | Ltd Slip | Std/Opt |
| THM350 | 3.8 (LC8) 3 | 2.41 | 6RB | 6BJ | STD |
| THM350 | 3.8 (LC8) 3 | 2.73 | 6AB | 6BB | OPT |
| THM350 | 3.8 (LC8) 3 | 2.73 | 6RD | 6BB | STD |
| THM350 | 3.8 (LC8) 3 | 3.08 | 6AC | — | OPT |
| THM350 | 3.8 (LC8) 3 | 2.41 | 6RB | 6BJ | STD |
| THM350 | 3.8 (LC8) 3 | 2.73 | 6AB | 6BB | OPT |
| THM350 | 3.8 (LC8) 3 Calif | 2.73 | 6AB | 6BB | STD |
| Gear Ratio | Ring Gear | Assembly Codes |
| 2.29 | 7.5″ | AH, BH, AT, BT |
| 2.41 | 7.5″ | AJ, BJ, AZ, BZ |
| 2.56 | 7.5″ | AY, BY |
| 2.73 | 7.5″ | AX, BX, RX, AB, BB |
| 2.93 | 7.5″ | AG, BG, AW, BW |
| 3.08 | 7.5″ | AC, BC, AV |
| 3.23 | 7.5″ | AU, BU |
1981
| Trans | Engine | Ratio | Peg Leg | Ltd Slip | Std/Opt |
| M64/Man 3 | 3.8 (LD5) | 3.08 | 8AC | 8BC | STD |
| 2.41 | 8AJ | 8BJ | STD | ||
| MX2/350C | 3.8 (LD5) | 3.08 | 8AC | 8BC | OPT |
| 3.23 | 8AD | 8BD | OPT | ||
| MX2/350C M33/350 | 3.8 (LC8) | 2.73 | 8AB | 8BB | STD |
| 3.08 | 8AC | 8BC | OPT | ||
| MV9/200C | 4.3 (LS5) Diesel | 2.29 | 8AH | 8BH | STD |
| Gear Ratio | Ring Gear | Assembly Codes |
| 2.29 | 7.5″ | AH, AT, BH, BT |
| 2.41 | 7.5″ | BJ, AJ, BZ, AZ |
| 2.56 | 7.5″ | BY, AY |
| 2.73 | 7.5″ | AB, BB, AX, BX, RX |
| 2.93 | 7.5″ | AG, BG, AW, BW |
| 3.08 | 7.5″ | AC, AV, BC |
| 3.23 | 7.5″ | AU, BU |
1982
| Trans | Engine | Ratio | Peg Leg | Ltd Slip | Std/Opt |
| 2.41 | 2AJ | 2BJ | STD | ||
| MX2/350C M31/250C | 3.8 (LD5) | 3.08 | 2AC | 2BC | OPT |
| 3.23 | 2AD | 2BD | OPT | ||
| MX2/350C | 3.8 (LC8) | 3.08 | 2AC | 2BC | STD |
| MX2/350C | 4.1 (LC4) | 2.41 | 2AJ | 2BJ | STD |
| MV4/350C MV2/350C | 5.7 (LF9) | 2.29 | 2AH | 2BH | STD |
| MV4/350C MV2/350C | 4.3 (LT6) Diesel | 2.41 | 2AJ | 2BJ | STD |
| 2.56 | 2AA | 2BA | Hi Alt STD |
| Gear Ratio | Ring Gear | Assembly Codes |
| 2.41 | 7.5″ | BJ, AJ, BZ, AZ, BM, AM, CC, CQ, RZ, CU, RB, CH |
| 2.56 | 7.5″ | BY, AY, CE, CN, CI, CV, BA, AA, RC, CL, CY, RY, RD, CM, CZ |
| 2.73 | 7.5″ | AB, BL, AL, AX, BX, CW, CD, CR, BB, RX, CJ |
| 2.93 | 7.5″ | AG, BG, AW, BW, RW |
| 3.08 | 7.5″ | AC, BC, AV, RF, RV, BV |
| 3.23 | 7.5″ | AD, BD, AU, BU, RG, RU, AE, BE |
1983
| Trans | Engine | Ratio | Peg Leg | Ltd Slip | Std/Opt |
| 2.41 | 2AJ | 2BJ | STD | ||
| MX2/350C M31/250C | 3.8 (LD5) | 3.08 | 2AC | 2BC | OPT |
| 3.23 | 2AD | 2BD | OPT | ||
| MX2/350C | 3.8 (LC8) | 3.08 | 2AC | 2BC | STD |
| MX2/350C | 4.1 (LC4) | 2.41 | 2AJ | 2BJ | STD |
| MV4/350C MV2/350C | 5.7 (LF9) | 2.29 | 2AH | 2BH | STD |
| MV4/350C MV2/350C | 4.3 (LT6) Diesel | 2.41 | 2AJ | 2BJ | STD |
| 2.56 | 2AA | 2BA | Hi Alt STD |
| Gear Ratio | Ring Gear | Assembly Codes |
| 2.41 | 7.5″ | RB, CC, AJ, AM, BM, CG, BJ, RZ, CH, AZ, BZ, CU, CK, CX |
| 2.56 | 7.5″ | RC, CE, AA, CN, BA, CI, AY, CV, BY, RY, CL, CY |
| 2.73 | 7.5″ | RD, CD, AB, AL, BL, CR, BB, RX, CJ, AX, CW, BX, CM, CZ |
| 2.93 | 7.5″ | RE, AG, BG, RW, AW, BW |
| 3.08 | 7.5″ | RF, AC, BC, RV, AV, BV |
| 3.23 | 7.5″ | RG, AD, BD, RU, AU, BU |
| 3.42 | 7.5″ | AE, RK, BE |
| 3.73 | 7.5″ | AF, BF |