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Ford 9-Inch Currie TwinTrac

Currie TwinTrac Helical-gear limited-slip differential (LSD) is the modern replacement for the classic clutch-style Posi. Under normal driving conditions, the TwinTrac operates like an open differential, allowing the wheels to spin at different speeds to negotiate turns smoothly.

However, when accelerating, if a tire begins to lose traction, the helical-gears inside the TwinTrac automatically engage, applying power to both rear tires to maximize traction. When the acceleration (torque) lessens, the differential resumes regular operation. The TwinTrac is maintenance-free and will maintain its high torque bias for the unit’s life as it contains no clutches or springs that can wear-out.


  • Helical-Gear Style Limited-Slip Differential
  • High Torque Bias Drives Both Wheels for Maximum Traction
  • Reliable and Predictable Traction With Smooth, Seamless Operation
  • No Clutches or Springs to Wear-Out
  • No Special Lubrication or Friction Modifiers Needed

Technical Details:

  • Accepts 31-Spline Axles
  • Bearing Journal 1.780

Gear Oil Recommendations:

  • For all 9-inch applications, Currie recommends 85W-140 weight GL6 rated petroleum-based gear oil
  • Synthetic oils are not recommended for 9-inch gears or the TwinTrac limited-slip differential
  • Friction modifiers should not be used, as they will decrease differential bias and negatively impact performance

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