By Brian McCormick
The evolution of suspension designs, especially in the after market, is a never-ending challenge.  Depending upon the application, suspension innovators are constantly designing and testing different types of equipment that provide both ease of installation and proper function. But despite all the variety, one style of suspension remains dominant in the custom automotive market.  The very versatile parallel four-bar, or four-link as it is commonly known, has become a standard for many forms of auto racing, as well as the custom truck scene. Exchanging a stock, leaf-spring rear suspension for a four-bar setup not only provides improved traction, but also the benefits of  stability and enhanced ride. Ecliptic leaf springs tend to twist, while tubular four-bars don't twist at all. They firmly keep the rear end in place laterally, while allowing the housing to travel up and down as allowed by the shocks and springs. 
Recently, the folks at Classic Performance Products invited us to follow along as a parallel four-bar kit was installed on the frame of a '55 Chevy truck. The design of the kit, which includes brackets and components that utilize factory frame holes for accurate positioning, allows even a novice customizer to install it in only a matter of hours. A new frame cross member that provides upper mounting for the Aldan coilover shocks replaces the stock version that once resided over the rear end housing.  Other rear end modifications, seen here being applied to a new Currie rear end, will include a bolt-on Panhard bar mount that attaches to the third member, as well as lower shock brackets that need to be welded to the axle tubes. All of the necessary hardware is provided, including optional stainless steel or cad-plated components, and each rod end features polyurethane bushings. 
Installing a four-link rear suspension has never been so easy. It is truly one of the simplest kits to install and it works great too.  Whether you're going for the pro street look, or just want a high-tech rear suspension that functions, rides and performs better than the old, squeaky leaf design, this could be the kit you're looking for. In addition, if you add up the cost of purchasing a new pair of shocks, mono-leaves, pins, bushings and other equipment, the difference is only about $200. Follow along as we take you through the steps and decide for yourself. Then give Classic Performance Products a call to order your own rear parallel four-bar kit.
To make the installation a little easier to understand, the Classic Products four-bar installed on this bare '55 Chevy truck frame so it can be seen
To begin, the front stock spring hanger is removed from the frame. The kit includes a new hanger that is designed to accept the four-bar suspension and bolts to the same location.
Since the kit uses larger mounting hardware, the two stock hanger holes on the side and the two underneath must be drilled out with a 7/16-inch bit.


Once the holes are enlarged, the new front hanger can be bolted to the frame using the provided hardware.
The upper four-bar mounting hole must be drilled into the frame. This is done with a 5/8-inch bit, as shown.
The three stock holes that once positioned the rear spring snubber bracket also need to be drilled out to mount the new Panhard I bar bracket. This step requires a 7/16-inch bit and is done only on the driver's side.
Once the holes are drilled, the Panhard bar bracket is mounted to the inside of the driver's side frame rail.
The next steps involve removing the stock rivets that attach the frame crossmember located over the rear end housing. it's the fourth one from the front of the frame. The entire crossmember is removed to make room for the new version in the kit.
The new crossmember simply slides right in between the frame rails and lines up with the stock rivet holes. Make sure the shock attachments are facing forward.
To mount the crossmember, both the upper and lower holes must be drilled out with a 7/16-inch bit.
Using the provided hardware, attach the crossmember with the lock nut on the bottom.
For this particular installation, the customer chose a new Ford nine-inch rear end. The following steps will also apply to your own rear end selection, whatever it may be. Here we are measuring the overall width of the rear end from the inside of the backing plates to determine the housing center.
The center must also be marked on the new lower coilover shock brackets that will be welded to the rear end housing.
From the predetermined housing center, measure 18 inches towards the ends and mark the distance.
Here 's the tricky part. You want to position the lower brackets on the housing in a manner that establishes a four-degree pinion angle. This can be done by either leveling the rear end and the pinion, then positioning the brackets al the required four degrees, or positioning the rear end pinion at four degrees and attaching the brackets at 90 degrees.
With the proper bracket position determined, the lower shock brackets can be welded to the housing.
The rear end Panhard bar bracket attaches to the passenger side of the housing, using the existing third member bolts.
With that complete, the rear end can now be slid under the frame and secured on jack stands.
The bars that make up the four-link design are strong and beefy, and feature polyurethane and steel bushings. 
Attaching the bars is as easy as it gets. Simply insert the rod end into the front brackets, the stationary end into the rear, and bolt together with the provided hardware. Adjustments to the bars can be made later.
It is also recommended that the hardware be attached so that the lock nuts are on the inside of the bracket.
Next, we install the Panhard bar on the frame bracket and the rear end bracket.
The Classic Performance Products four-bar kit uses Aldan American Eagle shocks with powder coated springs for great ride and adjustability. The coilovers attach to the upper crossmember and any one of the three holes provided on the lower bracket.
And there you have if a reasonably priced custom suspension that features the luxury of ride height and quality adjustment. Better yet, it is extremely easy to install.

Classic Performance Products  378 E Orangethorpe Ave.,  Placentia CA 92870  Tech Line 714-522-2000


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