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The 9-inch Ford has long been the rearend of choice for the majority of drag racing applications, and for good reason, since its beefy ring and pinion gear have proven reliable, the aftermarket supports it with a huge assortment of gear sets with ratios that range from 3.00 to 6.50, and its carrier design facilitates easy gear changes.

Front and rear views of an M-W third member — the unit on the left sporting aluminum caps and steel caps employed on the right. You can also see the Thru-Bolt feature developed by Mark Williams where the caps are secured to the case from the front and the caps are precisely located via dowels.

With racers continuing to up the ante in engine power, the 9-inch Ford has been modified to accommodate 9.5- and 10-inch pitch diameter ring gears to provide the required reliability. Mark Williams Enterprises, the company credited with developing the first modular aluminum rear axle housing, has long focused on manufacturing race-ready third members to enable racers to take advantage of gear ratios best suited to track conditions.

Of course, it all starts with the case (or carrier). The OEM cast iron Ford case has been supplanted by nodular iron versions. Many years ago Williams developed an aluminum case with the innovative Thru-Bolt design that improves structural rigidity by securing the bearing caps, with bushings for precise cap alignment. The case itself weighs 11 lbs. less than the nodular iron version. Caps are available in 7075-T6 aluminum or steel. They are equipped with M-W’s Grip-Lock steel adjusters and available for larger bearing sizes.

Experienced technicians can set up third members for optimum efficiency using special “low friction” components and techniques.

Another benefit of the 9-inch Ford is the beefy pinion support, which has been improved upon over the years to keep pace with the horsepower race. M-W offers both nodular iron and aluminum pinion supports, with varying bearing options. The nodular iron pinion support, which is primarily used in oval track applications and iron cases, comes with angular contact ball bearings for improved efficiency.

M-W’s aluminum pinion supports are available for 9-, 9.5-, and 10-inch ring and pinion gear size differentials. They use Timken bearings that have a much higher load capacity than the OEM Ford units, with single or dual angular contact bearings providing improved reliability and reduced pinion movement.

Rear view of an M-W thirdmember from the right hand and left hand sides. They are available with a choice of steel or aluminum caps.

Given the variety of ring and pinion gears on the market, Williams manufactures supports that are designed for 28-, 32-, and 35-spline pinion gears. As is the case with axles, the more splines the better.

Increases in torque and shaft RPM brought about the development of pinion supports with rear angular contact ball bearings in lieu of conventional tapered roller bearings. They provide increased rigidity, as well as offer less frictional resistance. For optimum efficiency, M-W uses ceramic balls —which are stiffer, lighter and have a higher RPM rating.

Williams attaches the ring gear to the spool employing special ARP bolts and safety-wired to prevent them from loosening.

Recently, a 4.000-inch diameter bore Thru-Bolt aluminum case has been added to 3.062-, 3.250-, and 3.812-inch offerings. The larger bearings add to the third member’s reliability and allow for larger spline axles.

Williams offers the 4.000-inch bore Thru-Bolt case as part of it’s “Pro Mod” package that includes a 40-spline lightweight steel spool, a ball bearing pinion support with 1350 or 1480-series pinion yokes, plus big 10-inch pitch diameter gears (actual physical diameter 9.5-inch). That said, M-W offers some two dozen third member packages to cover applications from Pro Mod down to E.T. bracket cars.

For lightweight, relatively low powered drag cars and street applications M-W has third members with the special lightweight case (non-Thru-Bolt) that’s 15 lbs. lighter than an iron case.

M-W’s cases are available to accommodate 3.062-, 3.250-, 3.812- and 4.000-inch diameter bearings. The larger bearings provide support for 40-spline axles.

A special Hi-Efficiency third member is also available for lightweight cars (2,200 lb. maximum) and power limited to 1,000 horsepower. It’s perfect for a number of Competition Eliminator-style cars. This unit features a special case with the same pinion offset (hypoid) as the Dana 60 is known for. It’s a Thru-Bolt design, will fit in regular 9-inch and M-W modular aluminum housings. It employs special 9310 alloy gears that have been micro-polished (M-W Supra-Fin process) and precisely set up to reduce friction.

Pinion gears for the 9-inch Ford come in 28-, 32- and 35-spline configurations, with —as is the case with axles— the more splines the better.

For higher horsepower cars there’s the 9-1/2-inch Low Friction Ford third member that is the latest development in fighting performance losses due to friction. It features 9-1/2-inch diameter ring  gears with 32-spline pinions (same size as the transmission) with the gears micro-polished and Sub-Zero thermally treated to eliminate the possibility of retained Austenite. M-W’s Sure-Lock adjuster system prevents adjuster back-out. The units come with a computer pick-up rings and necessary magnets.

Here’s a race-ready thirdmember ready to go. The Thru-Bolt design to secure the caps was developed by Mark Williams.

And for handling the brute power of turbocharged, supercharged, or nitrous oxide-boosted motors Mark Williams lineup features 10-inch Severe Service Ford third members. These employ 10-inch pitch diameter Pro gears, steel caps, a steel spool, 1350 or 1480-series Yokes and 3.812- or the new 4.000-inch bore cases.

All M-W third members come with a free transporting case and three quarts of special SAE 85-140 gear oil developed by Torco to M-W’s specs (Mark Williams logo is on the bottle).

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