Racing Tech: Hooking Up Your Leaf Spring Suspension Without Traction Bars

(Image/Wayne Scraba)

Bolt-on traction bars for leaf spring cars have been available for what seems like forever.

They work, and there are all sorts of different versions out there: slapper bars, sliding link bars, bars with rollers on the leaf pack, bars with a rocker designed to rotate into the spring eye and so on. All of them hang down below the spring (some hang down so far that they can get hung up on trailers or other unmovable objects).

Some obviously work better than others.

Some folks though, can make leaf spring cars work (and work rather well) without the use of any traction bars.

Don’t believe us? Ponder the case of the stock appearing muscle cars campaigned in the Supercar Races series.

Case-in-point: There is a 1969 Nova that is one of the quickest cars there. The Nova’s best ET is 10.481 at 132.34 mph. It has a short time (60-foot) of 1.61 seconds. That’s hauling—especially when you consider it gets there on belted bias-ply skinny tires and with no traction bars of any sort.

And that’s not the only super-quick leaf spring car in the bunch that runs sans-traction bars. A 1963 Max Wedge car has run 10.94 @ 126.60 mph (in 2013) while a 1969 Camaro has run 10.495 @ 134.77 mph (in 2014). Additionally, there are a bunch of other cars hovering around the 11-second flat zone, so these really aren’t flukes.

How do they do it?

Dig deep and you’ll find all of the really quick leaf spring combinations run leaf springs with a decided forward bias (where the front of the spring is stiffer than the rear).

It’s not a new idea. The “old” Chrysler Corporation came up with the concept in the early 1960s. Chrysler engineers knew that when the hammer was dropped at the starting line, the front of the spring pack would wrap up (typically in an “S” shape). That’s when they designed springs with a heavier front bias. In some cases, the springs were heavily clamped forward of the axle housing. Often, the back of the spring pack was run without spring clamps or maginally clamped (one clamp).

Those springs with the biased front segment were aptly named “Super Stock” springs. They were designed to be used without any form of traction bar, other than a pinion snubber. In fact, Chrysler warned not to use any form of traction device in conjunction with their biased front Super Stock springs.

Chrysler continued to catalog various rate Super Stock springs for years and many are still offered today. Currently, Summit Racing stocks several Mopar Performance Super Stock springs. Of course, all of these are for Chrysler applications. What if you have something like a vintage Chevy Camaro or Nova or Pontiac Firebird?

Years ago, you could purchase Chrysler Super Stock-style springs for Chevys from a company called Tri City Competition. They were sold under the “Launcher” name, but those springs are no longer available. And yes, some of the super fast, stock-appearing muscle cars use these springs.

If they’re not available, are we back to square one? Maybe not. There are several applications in oval track racing where leaf springs are mandated. And vintage Camaros and Novas are a common platform. AFCO Racing has a line of special springs engineered with a new secondary leaf design that “provides improved forward bite.”

According to AFCO, the springs also reduce wheelbase variations during braking and acceleration to improve overall handling consistency.

These springs are available with several different rates, the most common being 153 pounds or 176 pounds. They measure 53.5-inches eye-to-eye and have a true arch of 6-3/8-inches (this is very close to the stock arch). The eyes are standard GM sizes—2.0-inches in the front and 1.5-inches in the rear.

AFCO Racing claims their leaf spring is the highest quality racing spring available today, and provides features not available in any other leaf spring. For example, their multi-leaf spring is constructed from high-quality chromium vanadium steel (springs can be manufactured from carbon steel, nickel-chromium steel, a nickel-chromium vanadium steel mix and and finally chromium vanadium).

Following an oil temper, chromium vanadium provides for the highest tensile strength per pound along with the highest elastic limit in pounds per square inch when compared to other springs. It also provides for rate consistincy over time.

AFCO heat-treats the spring to provide long life and they also shot-peen the spring after arching in order to relieve stress in the materials. They claim this process provides 3-5 times more service life to the spring. The respective leafs are tapered which reduces stress (by 30-40 percent, AFCO says). The tapered leaf design also prevents loss of arch. They include Teflon rub blocks between the leafs. This reduces friction between the leafs and helps to maintain consitency of rate.

The 176-pound rate springs are the most popular for stock big block combinations.

In terms of installation, these springs are a bolt-in for various Camaros and Novas. The springs have an arch of approximately 6-3/8-inches (which is close to stock or marginally higher). They include a front spring eye bushing (installed) and they accept a stock rear bushing (next month, we’ll look at spring bushing options—you might be surprised at what’s available and what you accomplish with them—stay tuned).

One more trick out of the stock-appearing racer’s notebook is the use of extra spring clamps. Summit Racing offers several different bend clips for leaf springs. These can be used as tuning tools for leaf spring cars with no added traction devices. Another option is to simply build your own with a couple of heavy steel straps and a pair of high-strength bolts and nuts.

So, does this setup work?

The truth is, most of the fast guys aren’t exactly talking (entirely understandable, we’d say), but when you ponder how hard many of those stock-appearing muscle cars run, you can draw your own conclusions. For a closer look at “the hook factor,” check out the accompanying photos:

At first glance, the AFCO race spring sold by Summit Racing looks pretty much like a stock replacement leaf. But that isn’t the case. There are considerable differences. (Image/Wayne Scraba)

When you examine the front segment of the spring pack on each leaf you’ll find it’s heavily (forward) biased – similar to an old Chrysler super stock spring. There are more leafs in the front than in the back. (Image/Wayne Scraba)

Here’s a look at the back segment of the spring pack. Compare this to the previous photo. (Image/Wayne Scraba)

Note the partial leafs in the spring pack. The idea with the forward bias in these springs is to control spring windup (where the front of the spring goes “S” shaped under power). (Image/Wayne Scraba)

Note the partial leafs in the spring pack. The idea with the forward bias in these springs is to control spring windup (where the front of the spring goes “S” shaped under power). (Image/Wayne Scraba)

In addition to more leafs in the front spring segment, the AFCO race spring also incorporates double clamps.

Out back, there is only one clamp used. This too is similar to the arrangement Chrysler used on their super stock springs. (Image/Wayne Scraba)

Something Chrysler didn’t do was to use Teflon “buttons” between the respective leafs. The idea here is to reduce friction between each working leaf. There are three buttons in the front segment and two in the rear. (Image/Wayne Scraba)

Some leaf springs don’t use a reinforcement under the pin bolt. As you can see, AFCO includes it with their race leaf springs. (Image/Wayne Scraba)

Something else to note is the location of the second leaf on the nose of the spring. It’s ends directly under the eye – just like the ultimate snubber location for a slapper bar. (Image/Wayne Scraba)

That second ends right here, just aft of the pin. (Image/Wayne Scraba)

The springs are supplied with an OEM style (and diameter) rubber front bushing. For street-strip or drag race applications, you might want to change out the bushing for something less pliable. (Image/Wayne Scraba)

Out back, the spring is sold without a rear bushing. You can either choose to use a stock style rubber arragement or something more exotic (again, we’ll dig into that next time around). FYI, the back eye is setup for a stock 1.50-inch diameter bushing. (Image/Wayne Scraba)

Note the leafs are tapered. This contributes to less stress in the spring pack. By the way, if you’re tuning these springs, this location at the front of the spring pack might be a good spot for an extra clamp. (Image/Wayne Scraba)

AFCO builds these springs with dimensional specs that prove very close to OEM. The arch is approximately 6-3/8-inches which will provide for a ride height that is stock or very close to stock. (Image/Wayne Scraba)