General Motors started using 14-bolt rear axles in trucks and vans in the early 1970s, so they have been around for decades. As such, the full-float axles are plentiful and salvage ones can be had fairly inexpensively. Even in factory form they are stupid-strong. In fact, a salvage 14-bolt axle may very well offer the most automotive advantage you can get for your dollar. With a hefty 10 1/2-inch-diameter ring gear, this heavy-duty axle makes for some good hardcore hardware to allow you to confidently run big treads.
But there’s always a catch. With all the beef and a sizeable ring gear, the differential housing is quite large and hangs down in the way of trail obstacles. However, Ballistic Fabrication offers a 14-bolt axle shave kit that gains you an additional 2 inches of ground clearance under the center of the differential housing. The kit includes an armored differential cover, a bottom differential block, and the necessary hardware. The bottom block is 5/8-inch-thick billet steel with an added 1/2-inch-thick armor plate ready to meet any boulder.
It is possible to install the Ballistic Fabrication kit at home with some skillful cutting and grinding. Ballistic provides full instructions showing you where to make the cuts in the bottom of the differential housing, and one of the employees offered the tip that a reciprocating saw works well for most of the cutting. If you have access to a good-sized mill with a table large enough to accommodate the axlehousing, you can machine away the offending metal.
Taking off a big chunk of the bottom of the housing means you are shedding some weight you could do without. It also means that the big 10 1/2-inch ring gear will no longer fit in the downsized centersection. The diameter of your ring gear will need to be reduced a bit. If you don't have access to machine tools to turn down your gear, Ballistic offers machining service at a reasonable cost, or it carries new gearsets with the ring gear already machined. The reduction should cause no real loss of gear strength.
We followed along as Ballistic milled a housing, machined a new ring gear, and added the shave kit and new truss assembly to a stripped housing. From there, the guys at Done Right Diesel added all the necessary mounts onto the housing and completed the final assembly of the high-clearance, fortified axle.
Here is the salvage 14-bolt donor housing we used. OEM replacement parts are fairly well available for this axle, but it is best to start with a complete axle assembly from the beginning to save time and money chasing down missing pieces.
Ballistic Fabrication mounted the bare axlehousing onto an angled fixture it uses on top of the mill table, then lifted both using a forklift.
Machinist Jason Faust used a carbide mill bit to make multiple passes and remove roughly 2 inches from the bottom of the differential housing.
Here are the shave kit components. If you are doing the work using handheld power tools, Ballistic recommends bolting the new cover in place on the axle. Then the cut line can be marked. The instructions show that the cut should be made at 6 degrees past horizontal.
With the machining complete, Jeff Ketz checked the fit of the bottom plate against the cover and the differential housing. The mill left the housing perfect for welding, but this is the point when you would make any final adjustments in fit using a grinder. Ketz preheated the cast housing with a torch to about 300 degrees F to prepare for welding.
Ketz used a MIG welder feeding 0.045-inch wire to burn the new bottom plate onto the differential housing. The new rear cover is CNC cut and formed from 3/8-inch-thick steel plate so it's a heavy-duty addition.
Ketz also welded the bottom plate from the inside. You can see where he fully welded the circumference of each axletube to the cast housing to further strengthen the joint there.
With the welding complete on the cast housing, it was covered with a fireproof blanket for an hour or more to allow the housing to slowly cool to reduce thermal stress and prevent cracking at the weld areas.
A Ballistic truss kit was also prepared for installation on the axlehousing. The kit comes in multiple pieces, some already bent where needed. They are laser-cut with slots for easy assembly. Here Ketz begins tacking the pieces together.
The tack-welded truss was checked for fitment and ground slightly where needed to achieve a good fit to the axletubes.
The new rear cover was reinstalled and checked for alignment to the mating truss holes. Then the truss was welded to the axlehousing.
All the mounts needed for the suspension links, shocks, limit straps, sway bar links, and brake lines were added at Done Right Diesel. After a fresh coat of paint on the axle, Mark Mason began gear installation by dropping the prepared pinion support assembly into the housing.
Ballistic had reduced the ring gear diameter to about 10 inches. You can see how it fits inside the new bottom plate. The steel plate is 1/2 inch thick, except for a small area below the gear that is about 1/4 inch thick.
With gear setup complete, the Ballistic rear cover was installed. Two bolts on top of the cover also tie it to the top of the truss assembly.
The original drum brake components on this axle were discarded, but the wheel hubs were reused. Ballistic bolt-on disc brake brackets were used that accommodate 1973-1987 Chevy K20 front rotors and calipers.
The Chevy 3/4-ton rotors were pinned to the back of the wheel hubs with new lug studs. The stock studs were swapped for longer 9/16-inch Dorman 610-194 studs to ensure adequate thread length to run aluminum wheels. Dorman 611-061 lug nuts were used.
A Wilwood Front Caliper Kit (PN 140-11290-BK) was used for this rear axle build. Done Right Diesel installed new hard-steel and stainless-braided brake lines.
The pinion support bolts were removed and the Ballistic truss brace/pinion guard bolted in place.
Here you can see the final assembly showing how the pinion support is bridged to the added truss assembly, similar to the rear cover mating.
With the full-float axleshafts installed, the completed axle was ready to be reunited with the rig.