It’s about the best factory suspension there is. The aftermarket equivalent is virtually identical in nature, and the triangulated upper bars are what set it apart from all the rest. These bars resist side-to-side movement because of the inward angle. This design eliminates the need for a panhard bar to keep the axle assembly from wandering side to side. However, this does not mean it is without fault.
In stock form, the bars with simple U-shaped channels can bend and twist under extreme use. Although the large rubber bushings provide an excellent ride, they are too soft and spongy for high-performance driving. Aftermarket upgrades include polyurethane bushings or even bearing conversions, and adjustable upper arms allow tuning of the pinion angle. Solid or tubular lower bars are another popular upgrade. The factory bars can be upgraded on the cheap by boxing them in. A plate is added to the open side of the channel, reinforcing the bars so that they do not bend or flex.
The axle housings for four-link suspensions have these upper bushings; this type of suspension is found on A- and G-Body cars. There is no easy way to remove these bushings and after years of use they are often worn or damaged. The best method is to use an air impact hammer and a chisel to crush the bushing end and then drive it out.
Once you have thoroughly cleaned the axle assembly, you should protect the surfaces. If you have stripped it down to the metal, it starts collecting surface rust immediately. So, it’s a good idea to paint the axle assembly to prevent rust from forming and to make it look fresh. A new coat of paint makes a housing look much better than a crusty, greasy one. If you’re not set up to paint it, you should coat it with WD-40 or some other lubricant to prevent rust from forming.
The springs are typically mounted to the housing for four-link suspensions, which makes removing them quite easy. The upper mounts are cast into the center section of the housing, which is a problem if you are looking to upgrade to a 12-bolt unit. You can’t just weld mounts to the housing as you can with a leaf spring or trailing arm unit. Instead, you need to find either a factory 12-bolt housing or purchase an aftermarket version.
The Corvette is the only regular production vehicle General Motors made that carried independent rear suspension. The 1963 through 1978 Corvettes were fitted with axles similar to the 10- and 12-bolt, but not exactly the same. However, conversions are available that use 12-bolt differentials in the C2 and C3 Corvette housing. Although a solid axle system is used in conjunction with a multi-link and leaf spring suspension system, an IRS system uses an independent axle shaft on each side, so both rear wheels can move independently according to road conditions and load on the suspension. The Corvette design, however, uses a transverse-mounted fiberglass mono-leaf spring, and that connects both sides of the axle.
Project: Building a Universal Axle
A universal axle is an indispensable tool when fitting a rear axle assembly to a vehicle (and it has several other uses). If you build many project cars and need to move them around, this is a good tool for you. How often do you wish you had a rolling axle that is adjustable for width and fits under anything? Although your initial answer may be “never,” you might be surprised just how often this rig comes in handy, especially if you buy/build a lot of project cars. This universal axle can be used as a custom rear-end jig, trailering axle, and car body mover.
I first discovered the universal axle during a drag car build. My axle builder, Harold Evans of Perkins, Oklahoma, designed and built this adjustable axle so we could set up the rear of the drag car to fit with the wheel and tire combo, and he used it as a jig to build the narrowed housing. With that accomplished, I have this heavy-duty axle that expands from 45-inch to 65-inch with the turn of a couple bolts, and it has multiple bolt patterns for whatever wheels are needed.
You need a few spare parts for this project. I used pieces from a mid-1960s Chevy truck, but you can use whatever you have available. If you have to buy the parts, they are typically available on Craigslist or at a salvage yard. Drum-brake front spindles are easy to find and super cheap.
Here is the basic parts list:
• Drum brake spindles and hubs: Bolt pattern only matters if you are setting it up to use a specific wheel. I drilled mine for 5-on-4.75-inch, the most common GM pattern, plus I left the six-bolt pattern.
• Square tubing: You need two sizes. One is for the outer section and one is for the sliding inner section. I used 3-inch mild steel for the outer and 2.5-inch mild steel for the inner. The tubing was about 1/4-inch thick, strong enough to hold up the back end of a car.
• A good welder and the ability to cut the tubing square. If you don’t have a metal bandsaw, you can have the steel shop cut it to size for you.
• Four nuts and bolts: A couple pairs of 1/2-inch nuts with 2-inch-long bolts lock the width of the axle.
The project is not complicated or extremely labor intensive so you can probably build it in a day. My machinist went the extra mile by fly-cutting the spindles on a lathe, but that is not absolutely necessary. Once you have one of these adjustable axles, you will find all kinds uses for it.
This project installs a tubular A-Body suspension. First, you need to build a dummy axle for suspension and axle fitment purposes. I used a set of drum spindles from a 1960s Chevy truck that had been converted to discs. You can also use late-model 4×4 front hubs, mid-1990s on up half-ton trucks work great. You can check with local shops for late-model 4×4 front hubs because they are frequently replaced. The bearings don’t have to be in great shape for this tool.
You disassemble the drum brakes to create the tool. Rivets often hold the drums to the hub; drill them out. I removed the cotter pin and castle nut that holds the rotor and hub on the spindle.
With the drum and rotor removed, the bolts holding the steering arms can be accessed. Use a socket and ratchet or wrench to remove the retention bolts.