Leaf spring suspensions have been around since the horse drawn carriage days. It’s simple engineering that provides a fairly comfortable ride, but when building a performance suspension they become a traction limiting weak link.
As power is applied to the rear axle rotational torque causes springs to wrap up, distorting their shape, causing changes in rear suspension alignment, and limiting travel range. This often results in a bind that can cause tires to lose traction or worse, it can cause wheel hop.
Experiencing these conditions accelerating out of a corner can create a potentially ugly situation. To try to eliminate these issues many of our Pro Touring based competitors have kits that replace leafs with a triangulated 4 link that’s similar to those found in GM full framed muscle cars.
A triangulated 4 link uses short and long control arms set at opposing angles to help keep the rear axle located and relies on a separate spring and shock for controlling travel over bumps and body roll control. Maybe a little better than leaf springs the 4-link still has issues with suspension bind in cornering as the upper and lower arms travel in different arcs.
To compensate for this GM control arms are flimsy with rubber bushings to allow a lot of flex for a smoother ride but that means loose and lousy performance. When you make these arms solid and stiff plus add stiffer bushings it actually creates a worse bind situation and can cause a 4-link car to become more twitchy, less predictable, throw off the front suspension travel and lose traction everywhere.
The main purpose of the rear suspension in better handling is to smoothly follow the front suspension and provide adequate travel range to keep the most amount of tire on the road at all times.
The best application for this in a street car is the 3-link style Torque Arm. Even GM eventually figured this out and adopted this set up in Camaros and Firebirds in 1982, sticking with this design until the 2010 and newer cars incorporated independent rear suspension.
More About Speedtech Torque Arm Systems
There is more to how a rear suspension works than just anti-squat percentages. A lot of folks don’t understand the torque distribution from the rear axle. Torque distribution is the measurement of how much torque is directed to lifting the chassis & loading the rear tires.
The suspension links & mounting points define how much the rear suspension is actually loading the rear tires for grip.
All Independent Rear Suspensions (IRS) have a 50%/50% torque distribution, because the diff is mounted to the chassis. Torque distribution can vary on solid axle linkage style suspensions … like 3-Links & 4-Links … depending on the distance the linkage mounts are above & below the axle centerline.
3-Link & 4-Link rear suspensions can also offer 50/50 torque distribution … but ONLY if the upper & lower link mounts on the housing are the same distance from the rear axle centerline.
Let’s say the lower link mounts are 6″ below the axle centerline & the top link mounts are 6″ above the axle centerline… that is a 50/50 torque distribution …which is pretty good. That means half of the torque rotation in the rear end is lifting on the chassis & loaded the rear tires … which creates good grip.
For race cars, adjustable 3-Links are the way to go, but only if you can make the top link housing mount AT LEAST as tall as the lower link mounts. This requires eliminating the trunk floor & back seat. Fine for race cars. Not for Street cars.
Unfortunately in most production muscle cars, when we lower the ride height, there is not much room between the rear end & the truck floor. So we can not fit tall top link mounts in there. Just won’t fit.
Some 4-link kits have the top links mounted just above the axle tube, which works out to around 3″ above axle centerline. In that situation we’re only getting 33% of the rear end’s torque distribution lifting on the car & loading the rear tires.
Some other 4-link kits have the top links mounted in front of the axle tube, which works out to 1″ above axle centerline. In that situation we’re only getting 17% of the rear end’s torque distribution lifting on the car & loading the rear tires.
Torque Arms allow the rear suspension to move freely, with no bind or resistance. The great advantages with Torque Arm rear suspensions is they fit on lowered trucks or muscle cars and provide 50/50 torque distribution, good rear grip without cutting up the trunk floor.
Axles & Torque Arms?
Mounts are available for three specific axle applications:
– GM 8.2″ or 8.5″ 10 bolt axles found commonly in muscle cars from the early 1960’s to late 1970’s. These rears were most common in small block applications in cars like Camaros, Chevelles, and Novas. The 8.2″ was in the earlier cars, 8.5″s were available around 1970.
– GM Car 12 Bolt axles were commonly found in GM muscle cars, most commonly found in big block applications. Note in the diagram that the 12 bolt car and truck rears are quite different.
– Ford 9″ axles that have factory Ford clocking bolt locations on the front pinion mount, (A.) in photo. Some aftermarket axles have Ford or non-Ford clocking. We have mounts that fit Strange, Moser and Currie. Be sure to tell your sales rep what brand axle you have!
Axles that will not fit our torque arm mounts
– GM Truck 12 bolt,
– GM BOP axles
– GM 7.5″ (G-Body/ S10)
– GM 7.625″ (’82-’98 Camaro/ F Body)
– Ford 8.8″