uilding a classic truck can be a challenge for one simple reason: they were never designed to do what we now expect of them. In most cases, the goal is to have a lower ride height, a smoother ride, and improved handling characteristics. The problem is none of those factors were considered when these haulers were designed and built. When these trucks were new they were meant to be tough and haul a load; they were destined to be utilitarian vehicles and little else mattered. So, the challenge when building a classic truck becomes making them more refined and cruising friendly.

Look under the rear of just about any classic truck and you’ll see one of two suspension systems—parallel leaf springs (transverse on 1941-and-earlier Fords) or coil springs on long control arms. Both are simple and effective but they can be improved for our purposes. With rear parallel leaf springs there are two simple options. The first is to install softer, re-arched springs. The second is to relocate the rear axle from below the springs to above. This is usually accompanied by removing the overload leaves, or installing new, softer springs.

Trucks with coil spring rear suspensions, such as Chevrolets and GMCs, had the springs mounted on long trailing arms. While it would seem easy enough to lower them by using shorter springs, the problem becomes U-joint angularity. Since the axle housing is clamped to the trailing arms, as the truck is lowered the pinion angle changes noticeably—not something you want as it can cause vibration and premature U-joint wear. The best option here is replacement trailing arms that allow the proper pinion angle to be maintained.

Some of the more popular rear suspension systems for trucks are four-bars, triangulated four-bars, and four-links. Four-bars consist of four parallel bars that position the axle housing in the chassis front to rear and some sort of a lateral locator, such as a Panhard bar or a Watts link. A variation on this theme is a triangulated four-bar. Two-bars run parallel with the framerails with two additional bars running at an angle from the axle housing to the frame that locate the housing side to side, eliminating the need for an additional link. While four-links are similar to four-bars, the difference is adjustability. Four-bars are normally parallel and have fixed mounting points (threaded ends allow minor adjustments for wheelbase and pinion angle adjustments) while four-links allow the attachment points of the links to be altered to tune the chassis. Four-links are most commonly used in drag racing to alter how the vehicle launches from a standstill.

A somewhat more exotic modification to the rear of a classic truck is the installation of an independent rear suspension system (IRS). One of the first wiggly rearends to be transplanted came from underneath Jaguars. Corvette IRS units from 1963-on have also been used (although the 1984-and-later design is vastly improved). Then there are the completely custom IRS systems available from a number of our advertisers—admittedly expensive alternatives, they offer superb performance and are unmatched in terms of bling.

Regardless of the type of rear suspension used, when lowering a truck it may be necessary to modify the framerails by stepping them or adding a C-notch for axle clearance. The challenge when doing this is to increase clearance and not reduce the strength of the frame. To that end many suspension kits include C-notch plates with the necessary reinforcements. Some kits include new frame sections that step up and over the rear axle, while strong and providing for the maximum amount of drop, modifications to the bed floor are usually required.

By choosing the proper suspension components for the rear of your classic truck you can meet the challenge of turning a working vehicle into something much more civilized. The stance will be improved and the ride and handling will be enhanced. That’s how you turn a workhorse into a thoroughbred.

3. This parallel leaf spring kit from Speedway Motors is for 1937-1953 Chevy pickups and comes with shocks and a crossmember. It allows the installation of an open drive rearend and lowers the ride height by 4 inches.

5. CPP’s rear suspension kit for 1963-1972 Chevys features tubular trailing arms. The kit includes a new center crossmember; notching plates, Panhard bar, and coil springs or coilovers are available.

7. This Art Morrison four-bar kit mounts the bars to the inside of the framerails for increased tire clearance on a wider frame.

9. Panhard bars are used to locate the rearend housing laterally, they may be in front of or behind the axle housing. In any case they should be as long as possible to reduce their arc during suspension travel, limiting any side-to-side deflection.

11. One of the most sophisticated means of locating a rear axle is a Watts link. The bellcrank allows the housing to move up and down without side-to-side movement. The example is from Art Morrison.

13. A popular rear suspension option is the air spring. Ride height is adjustable and can accommodate an increased payload if you do haul something in your truck with an air pressure increase.

15. A four-link allows for a wide range of adjustment thanks to the array of attachment holes for the links. Raising or lowering the bars impacts how weight is transferred, which impacts how the vehicle launches.

17. Roadster Shop not only does some of the best full truck chassis in the business, they also offer this trick bolt-in four-link for 1963-1972 C10s. Their Revo kit includes a beefy four-bar with Panhard, bolt-on frame brackets with integrated C-notch, Roadster Shop SV fixed-valve coilovers (by Fox), and Strange Engineering 9-inch housing with 31-spline axles!

18. One of the pioneers of aftermarket independent rear suspensions is Kugel Komponents. This example features cast stainless steel control arms and inboard disc brakes. Quick-change centersections are also available.

20. Here the original C4 Corvette crossmember that mounts the centersection can be seen. It and the centersection simply bolt in place with Flat-Out Engineering’s brackets.

22. This F-100 Ford rear suspension system from Scott’s features four-bars, coilovers, and a Watts link.