Section 6 (Differential - Positive Traction): Identification
WARNING: This page is about a different car, the 1991 Pontiac Firebird, 1991 Oldsmobile Custom Cruiser, 1991 Chevrolet Caprice, 1991 Chevrolet Camaro, and 1991 Buick Roadmaster. However, it is still accessible from the selected car via links, so may be relevant.
The differential can be identified as a positive traction unit by raising vehicle and rotating one rear wheel. With transmission in Neutral, both rear wheels will rotate in same direction if vehicle is equipped with a positive traction differential.
The axle may also be identified by axle code. Axle code is stamped on front of right rear axle tube and on tag attached by ring gear cover bolt. See Fig 1 . Axle ratio, ring gear diameter and differential type is contained in the axle code. Refer to AXLE RATIO IDENTIFICATION table.
AXLE RATIO IDENTIFICATION
| Application & Gear Ratio | Axle Code | |
|---|---|---|
| 7 5/8" Ring Gear | ||
| 2.73:1 | 8HE & 8HT | |
| 3.08:1 | 8HB & 8HF | |
| 3.23:1 | 2PM | |
| 3.42:1 | 2PN | |
| 8 1/2" Ring Gear | ||
| 2.56:1 | 4ZL | |
| 3.08:1 | 4NC | |
| 3.23:1 | 4YM | |
| 3.42:1 | 4ZJ | |