Nov. - Dec. 2001 Motor State Performnace Report Article By Jim Kaekel, Jr.
The 9" Ford rear end, so named because of its 9" ring gear diameter, was manufactured from 1957 to 1987 by the Ford Motor Company and installed in some intermediate and most full size Ford, Lincoln and Mercury passenger cars, F-Series 1/2 ton trucks and Econoline vans. Its overall strength and availability are its greatest attributes, and 9-inch units are available with either 28- or 31-spline, large diameter axles. The 9-inch housings, also noted for their sturdiness, were built with case thicknesses ranging from .150" to .250." Through the years, the 9-inch was offered in seven different housing widths, from 57-1/4" to 69-1/4", any of which may be suitable for a particular race or street vehicle. Many street stock circle track and drag racers prefer the 9-inch rear found in '66-'70 full size Fords and Mercurys, '71-'72 Lincolns and '68-'72 F100 Ford trucks because it has 31-spline axles, large ball-type axle bearings and a 61" overall width (measured from drum face to drum face). Some of these units also have large 3-1/4" axle tubes, rather than the standard 3." Remember though, that a traditional 9" third member must be exchanged for the unacceptable 9-3/8 ring gear found in most housings with the 3-1/4 tubes. Another favorite, especially with street rodders, is the '79-'81 Lincoln Versailles rear end. An extra thick wall housing, factory disc brakes, 28 spline axles, large ball type axle bearings, leaf spring mounting pads and a 58-1/2" overall width make it a natural swap in most cars of the thirties and early forties.
The removable center section of the 9-inch allows the ring and pinion gears to be set-up on a bench, rather than in the housing, and rear end ratios can be quickly changed. Racers can carry extra center sections with different ratios for experimentation purposes. Strengthwise, the most desirable center sections are those made from nodular iron, easily identified by a large "N" on the outside of the casting.
The aftermarket produces a wealth of heavy duty 9-inch rear end parts engineered for street and racing applications. Complete housings, carriers, spools, mini-spools, axles, housing ends, bearing and shim kits, pinion supports and yokes are all available from Ford Racing, Mark Williams, Strange Engineering, Currie Enterprises (9+), and Allstar Performance. Spools and yokes are available in steel as well as lightweight aluminum, and super light, but costly titanium. Ring and pinion manufacturers like Richmond offer a multitude of gear ratios.
There are several helpful hints to promote longevity of the Ford 9" according to the experts at Mark Williams. Most replacement 9" ring gears require modifications to prevent interference in the area of the case where the pinion pilot bearing is located. Rather than machining the housing, the ring gear should be carefully chamfered using a small die grinder to provide adequate clearance in this area. Rears used in oval track applications should have either a custom baffle or internal housing seal (Allstar #ALL72100-#ALL72104) installed to prevent gear oil from being built-up in the right axle tube. If a rear end is to use a stock Ford pinion support, it must be the one with the #HM89443 rear cone. When drag racers choose a set of Richmond standard pinion (1.313" dia., 28-spline) Pro gears, cone #HM89444, which features a larger radius to match the increased radius of the pinion, must be used.
A heavy duty pinion support is another worthy addition to any 9" rear. Heavy-duty "Daytona" style supports, (Allstar #ALL68395 or Mark Williams #MWE57620) available for standard 28-spline pinions with a larger bearing, are particularly popular with oval track racers. Drag racers who select a Pro gear set with a large diameter (1.875" dia., 35-spline) pinion must use a special Pro support (Allstar #ALL68390 or Mark Williams #MWE57630) that will accept the 35-spline pinion.
Finally, regardless of application, all 9" rears should be fitted with a bung and cap for easy filling. The specialists at Mark Williams recommend filling with four quarts of Torco 85W140 racing gear oil (Torco #TRC248514) for best lubrication.