A "posi rear end" refers to a Positraction differential, which is a type of limited-slip differential (LSD) popularized by General Motors, particularly in Chevrolet vehicles, during the 1950s, 60s, and 70s.
Understanding Positraction
Positraction, a branded name, is designed to improve traction by limiting wheel spin. In a standard differential, if one wheel loses traction (e.g., on ice or mud), it spins freely, sending power to the wheel with the least resistance and leaving the other wheel with little or no power. This can lead to a vehicle getting stuck.
A positraction differential (LSD) is engineered to mitigate this issue. Here's how it works:
-
Limiting Wheel Spin: It restricts the amount of differential action, meaning it attempts to send power to both wheels, even if one has less traction. This is done through various mechanisms, such as clutches or gears, that resist the difference in rotational speed between the two wheels.
-
Improved Traction: By transferring power to the wheel with more grip, positraction enhances acceleration, especially on slippery surfaces. It also aids in off-road situations where one wheel might be airborne or on loose terrain.
-
Not a Full Locker: It's important to note that a positraction differential isn't a "locker". A locker forces both wheels to turn at the same speed, regardless of traction. A positraction (LSD) allows some differential action, making it more suitable for street driving than a full locker, which can cause unpredictable handling and binding during turns.
Benefits of a Posi Rear End
- Enhanced Acceleration: Improved grip during acceleration, especially on surfaces with uneven traction.
- Better Handling: More stable handling in situations where one wheel might lose traction.
- Off-Road Capability: Increased capability on off-road terrains where traction is crucial.
Drawbacks of a Posi Rear End
- Increased Complexity: More complex design compared to a standard differential, potentially leading to higher maintenance costs.
- Noise and Jerkiness: Some positraction differentials can produce noise (clunking or clicking) during turns, and may feel slightly jerky at low speeds.
- Wear and Tear: The clutches or gears within the differential are subject to wear and tear over time, requiring eventual replacement.
In summary, a "posi rear end" or positraction differential is a valuable addition to vehicles where enhanced traction and performance are desired. It's a type of limited-slip differential that offers a balance between on-road drivability and off-road capability.
