Ford 9-Inch Third Member Assembly (31-Spline)

A complete Currie 9-inch third member makes updating your street rod, muscle car, or truck easy with a new gear ratio or performance differential. All Currie built-to-order third members feature a new gear case, bearings, seals, solid pinion bearing spacer, and Daytona pinion support, with a choice of gear ratio, pinion yoke, and differential type.

Currie 9-inch third members are assembled by our in-house experts with decades of rear end setup and assembly experience so that you can trust the finished product.

Currie 9-inch Third Member Features

		Gear Case - New Currie Sportsman 9-inch nodular iron gear case with 3.062 bore carrier bearings for 31-spline axles
		Pinion Support - New nodular iron big-bearing pinion support
		Pinion Yoke - Choice of 1310 or 1350 series short nodular iron pinion yokes
		Master Bearing kit - New Timken master bearing kit with seals and solid pinion spacer
		Labor - Fully assembled and set up in-house by skilled professionals

9-inch Third Member Options

		Gear Ratios - Select from a wide range of ratios. Currie uses only the highest quality Motive Gear Performance® series (Orange box) ring and pinion sets
		Differential Options - Choice of 31-spline helical gear limited slip, automatic or selectable locking differentials or a steel spool

Differential Options Explained

Currie TwinTrac, Truetrac, and Wavetrac - Helical gear limited-slip type differentials (HGLSD). The HGLSD is the modern replacement for the classic clutch-style limited-slip. HGLSDs function like a standard or open differential, allowing one wheel to spin faster or slower as necessary without the noise or stick-slip frequently experienced with clutch-style limited slip or automatic locking differentials. Under acceleration, if a wheel loses traction, the helical gears inside the differential automatically engage, transferring torque to both rear wheels. When the wheels regain traction, the HGLSD seamlessly transitions back to functioning as an open differential. Unlike the traditional clutch-type limited-slip, HGLSDs require no special oil additive or maintenance to replace worn and tired clutches. HGLSDs have no wearable parts, require no special oil additive or maintenance, and maintain their as-new functionality for life.

ARB Air Locker - The ARB is a selectable locking differential that allows the driver to positively lock or unlock the differential on demand with the flick of a dash-mounted switch. An onboard air compressor (sold separately) is used to apply the locking force. Once locked, the differential behaves like a spool, driving both wheels equally. When unlocked, the locker acts like an open differential, driving only one wheel at a time – usually the wheel with the least traction. The key benefits of the ARB Air Locker are its predictable behavior and legendary strength.

Detroit Locker - Automatic locking differential, designed to lock and unlock automatically when torque is applied in either a forward or reverse direction. When locked, it acts like a spool, driving both wheels equally. When coasting or rolling into a corner (no torque applied), the Detroit Locker unlocks and momentarily operates like an open differential, permitting the wheels to rotate freely. When torque is applied, exiting the corner, the unit locks and drives both wheels equally. The key benefits of the Detroit Locker are its rugged construction and superb performance. The only negative is that the automatic lock and unlock operation can create a clunking sensation that can be felt and heard in the vehicle.

Spool – The spool is the most straightforward and robust option but lacks differential action, as the spool's solid center joins both axles. Spools are not recommended for the street, as they place high twisting loads on the axles, increase tire wear, and negatively impact handling. Spools are typically only used for drag racing applications where straight-line performance is the only concern.

NOTES:

Lubrication Requirements - 9-inch rearends use a high-offset hypoid gear design that requires a severe duty 85w-140 gear oil with API GL-6 rating. Use of oil not meeting the GL-6 rating will damage the gears and bearings and void the Currie Warranty