Torque Arm Suspension Conversion
Suspensions for Pro Touring cars have become the new darlings of the aftermarket. Less than a decade ago, the best you could find was perhaps a composite leaf spring conversion for a '70 Camaro. Today, we have alternative suspension designs appearing almost daily from a slew of different companies. We decided to take a look at one innovative approach taken by BMR Fabrication that converts the second-generation Camaro or Firebird leaf spring rear suspension into a torque arm design using bolt-on parts.
A. In the BMR conversion, the original Firebird leaf springs were replaced with a pair of lower control arms that connect the rear axle to the leaf spring body mount. The adjustable BMR links are fitted with spherical bearings that allow the tuner to accurately position the rear axle in the car.
B. Replacing the leaf springs is a pair of coilover shock absorbers that allow the end user a broad range of ride height adjustment. The coilover shocks can be either single or double adjustable to facilitate tuning the handling characteristics but are not included in the basic torque arm kit. The coilover shocks are positioned on upper mounts that straddle the original subframe and can be bolted or welded in place.
C. Because a torque arm is essentially a three-link-type suspension, it cannot-by itself-laterally locate the rear axle assembly under the car. This job requires a Panhard bar or Watt's link. BMR chose a Watt's link for its adjustability. As viewed from behind, the Watt's link employs two lateral links bolted to opposite sides of the body and connects in the middle of the rearend to a center-pivoting lever. The advantage to the Watt's link is its greater sophistication and adjustability to establish the car's rear roll center.
D. The BMR system also allows pinion angle changes using a simple bolt arrangement.
E. The torque arm is a variation of the four-link rear suspension design. The lower control arms (or trailing arms) are located in a similar position, but the torque arm that's mounted to the rearend and to a crossmember at the front replaces the four link's two upper control arms. The torque arm's forward locating position is also the instant center.
F. BMR recommends frame connectors that not only add stiffness to the factory unibody but also serve as excellent locating points for the transmission crossmember and torque arm front mounting point. The front torque arm position uses a fore/aft sliding mount to eliminate binding as the rear suspension moves.
G. This Firebird also received front suspension goodies from BMR, including tubular upper and lower control arms, Afco adjustable shocks, an antiroll bar, and Aerospace disc brakes.
PARTS LIST DESCRIPTION PN SOURCE PRICE Torque arm system TAS006 BMR Fabrication $1,999.95 Front sway bar SB008 BMR Fabrication 189.95 Front upper and lower arms AAP003 BMR Fabrication 839.00
