1975 Chevy Laguna Gets Rear Suspension - Solidly Linked

The joints for Global West's lower control arm set (part No. TBC-13) also use a high-misalignment spherical bearing on the chassis end, but a Del-a-lum bushing on the axle side. The Del-a-lum bushing is a sandwich of durable Delrin and aluminum. Delrin offers a low-friction surface that's quiet and wear resistant, yet has very high resistance to deformation, making it ideal for this sort of thing.

So the bones of our Laguna's rear suspension consists of Global West's TBC-37 upper control arms with the SP-47 bearing kit, and the TBC-13 lower control arms. But maintaining the proper geometry is only half the battle. None of these things matter in the least if you can't transfer the load from the tire to the ground. Springs and dampers (shock absorbers) are responsible for that. In a heavy car like the Laguna, the right springs and shocks can make a huge difference.

The actions of a spring and a damper are intimately intertwined. A spring stores road energy--heavy springs store and release this energy more quickly, and light springs do it more slowly. On the racetrack, it helps to store and release the energy quickly, so the tire can stay in contact with the road, and act on the car. The only downside is that a spring oscillates, and that oscillation needs to be controlled by a damper. As a rule, a stiffer spring needs a stronger, more viscous damper to control oscillation. By extension, lighter springs need less dampening to control them. So springs and shock absorbers need to be conceptualized as a matched pair, whereby the spring is optimized for the road and the car's intended use, and the shock damper is subsequently designed to control the spring oscillation.

Springs are rated in pounds per linear inch of deflection. In the case of our stock Laguna spring, it takes about 125 pounds of force to compress the spring 1 inch. We substituted this for a Global West spring (part No. S-61) with a rate of 160 lb/in, which should allow the tires to follow the road contour at high speed much better. The stock shock absorber, however, cannot completely control the higher spring rate, and the oscillation that goes with it, so we brought another expert into our loop: QA1 Motorsports.

We decided that to get the most out of our improved suspension, we needed a double-adjustable shock, meaning that the amount of damping force can be set independently for both compression (when the tire is shoved up into the fender by a bump), and rebound (when the spring extends the tire downward, as with a pothole or dip). QA1's Stocker Star double-adjustable shock was the answer. If you have a Laguna or any '73-77 GM A-body, the proper double-adjustable Stocker Star shock for the rear is a part No. DTC-1661P, which has the proper range of travel for a near-stock ride height, or slightly lower. We discovered that due to our dropped ride height (we lost track when it got to be more than 2 inches) a shorter shock was required, so we substituted part No. DTC-1915P. Had we used the longer shock, we would've damaged it internally, rendering it useless. (Since Global West is a QA1 distributor, you should consult with their staff about your ride height so they can recommend the proper QA1 shock.)

Before we get on with the installation, one word about antisway bars. Our Laguna did have a rear bar from the factory, which we opted to remove. I've found that with a sufficiently stiff suspension all around, the rear sway bar becomes less crucial, and can even hurt handling. A rear sway bar in conjunction with a stiff rear suspension can cause oversteer, although intuitively you wouldn't think so. The reason is that a modest amount of rear body roll can actually help plant the outside tire earlier in the corner, and improve bite. A stock-type sway bar like ours is mounted to the control arms, with most of its mass being unsprung weight, so if we do elect to put one back on at a later date, it will be mounted to the chassis, and connected to the axle with end links.

Of course, no rear suspension can operate properly without a matching front suspension, and we haven't forgotten about that. The day following our rear suspension installation at Global West, we came back to do the front half. The difference is like night and day. We were concerned that it might be too stiff, but when we hit the road, we found it quite compliant, only much more sporting. Probably more than any other thing, we noticed that the car felt significantly lighter, even though we know otherwise. Where it would wallow and porpoise over bumps and dips, it's now tight and taught. All we lack is some time on a road course to tweak our QA1 shocks. Next month, we'll take the wraps off our Global West front suspension!