While it may be tough for Bow Tie believers to come to grips with, if you’re looking for a rearend for your Chevy that will endure endless abuse, the best course of action is to give that GM axle the heave-ho and substitute a 9-inch.
Introduced in 1957, and in production for 30-odd years, the Ford 9-inch quickly gained a reputation for ruggedness and became the hot rodder’s rearend of choice. When compared to a GM 12-bolt, the pinion of the 9-inch engages lower on the slightly larger ring gear, which increases tooth contact for more strength (there is, however, a slight increase in friction). Another notable difference is the method of mounting the pinion. The 9-inch uses a removable pinion support for the large front bearing, and at the rear is a third bearing that supports the end of the pinion to reduce deflection under heavy loads.
One of the obvious advantages of the 9-inch rearend is the basic design. Referred to as the Hotchkiss style, the case containing the third member, or the ring-and-pinion assembly, is removable as a unit. By comparison, the GM rearend is the Salisbury design with the third member mounted into the axle housing. For ease of gear changes the nod goes to the 9-inch.
Another important issue is the method of retaining the axles. The 9-inch uses pressed-on bearings and lock rings on the axles that are held in the housing with retainers bolted to the flanges on the axletubes. If an axle should break to the inside of the bearing (it’s highly unlikely that one would break outside the bearing) the wheel will stay attached to the housing. By comparison, the GM axles are held in the housing by C-clips inside the differential case. A broken axle can allow the remnants of the shaft, and more importantly the wheel, to separate from the car. (Out of fairness we should point out that C-clip eliminators for GM rearends are available but they require modifications to the housing). Along with the broken axle issue, the 9-inch axles are much easier to remove and replace.
While the Ford 9-inch had a long production life, it has been almost 20 years since an OEM version was produced, so as the availability of production parts began to dwindle, the aftermarket responded with new and improved components. One such component is the FAB9 axlehousing from Chris Alston’s Chassisworks. Designed to accept all 9-inch Ford-style differentials, the FAB9 uses a fabricated, fully welded centersection. Looking a little like something out of Star Wars, these centersections are strengthened with internal gussets.
After welding, the FAB9 housings are CNC-machined to ensure a leak-proof third member seal surface and establish tight tolerances on the remaining housing features. To complete the assembly, 3-inch axletubes are used and Ford big-bearing, late-model Torino or small-GM housing ends can be specified. Also available is a folded back brace assembly that can be welded on at the factory; it adds considerable strength to the housing without adding significant weight.
To make the FAB9 complete, Alston offers third members and axles from Strange. Centersections are available in nodular iron and aluminum and may be fitted with 31-spline Positraction, 31-spline Truetrac, or 35-spline S-Trac differentials. Aluminum third members are available for 31- and 35-spline axles and 40-splines with a spool. FAB9 housings are available with all the proper brackets welded on for a number of suspension systems, including Alston’s g-Bar and g-Link systems. VariShock coilover or air spring suspensions are also options, as are antiroll bar brackets for chassis-mounted (sliding-link) bars or axlehousing-mounted (splined-end) bars.
Chassisworks’ FAB9 offers improved performance, reliability, and adjustability when compared to a stock GM rearend. Thanks to Chassisworks there have never been as many 9-inch options to choose from, and it’s never been easier to slide one under a Chevrolet. And for those purists among us take heart, with a rearend named the FAB9 you don’t have to use the F-word.
1. The FAB9 includes a fully welded centersection, housing filler assembly, vent, magnetic drain plug, and a choice of CNC-machined housing ends. Note that our housing has a back brace and the triangulated four-bar brackets are in place.
2. Before assembly, the housing should be thoroughly cleaned internally. We used a shop vac, grease remover, compressed air, and half a roll of shop towels to make sure nothing would contaminate the new innards.
3. Included with the housing is a hardware kit that contains the third member attachment bolts with copper washers, a plug for the filler, and magnetic drain plug.
4. Alston offers completely assembled 9-inch third members from Strange Engineering. Cases are available in nodular iron and high-grade aluminum.
5. Depending on the dropout used, Strange offers ring gears from 3.40 to 4.86:1. Complete third members come with the gearsets properly adjusted, as the pattern on these gears shows.
6. U-joint yokes are 1350 series and are available in steel or chrome-moly. Pinion supports are the heavy-duty Daytona style.
7. For our application we will be using Wilwood disc brakes, which include internal expanding parking brakes that work inside drums that are part of the rotors. The bearing retainers are open ended so they can be installed after the wheel bearings.
8. The FAB9 axles use press-fit bearings with lock rings to hold the axle in the housing, which means the wheel cannot separate from the housing in the event that a shaft breaks. Note the O-ring oil seal on the bearing.
9. A hole in the axle flange provides access to the bearing retainer fasteners. Strange axles are available in two series. The S-Series are induction-hardened for street, strip, or track use; the Pro Race series is thru-hardened for dedicated drag racing applications.
10. Our FAB9 housing has mounts for Alston’s g-Bar/g-Link suspension. Housings are available in stock widths or narrowed in 1/4-inch increments with the lower axle brackets and control arms moved inward.
11. Wilwood’s rotor attached to the combo hat/parking brake drum with a series of cap screws. They are installed with thread locking compound and are safety wired for security.
12. The Wilwood caliper mounts bolt to the axlehousing. The calipers are then attached to the two studs on the mount. Note the bracket to the right designed to accept the parking brake cable.
13. Our Wilwood rotors are vented, cross-drilled, and slotted for maximum stopping power. The rotors, with the integral parking brake drum, slide onto the studs and are held in place by the wheels.
14. We opted for Wilwood’s six-piston calipers. Using what is called a Radial Mount, shims are used on the axle mount bolts and the studs to properly position the caliper on the rotor.
15. Here’s the completed axle assembly ready to slip under our 1969 Camaro.