Why Isn't Everyone Using the C5 or C6 Corvette Suspensions?
Simply put, once the cradle and IRS assembly are removed from the C5 or C6 donor car, the upper control arms and shock absorbers have nowhere to go – because their upper mounting points remain on the unibody frame of the Corvette.
Below left is a closer view of the rear frame, with its upper control arm mounts, shock mount and the lower aluminum cradle, which is still attached to the underside of the frame. Below right is the same view for the front suspension mounts.
Below left is the C5 aluminum front cradle – below right is the C6 aluminum front cradle.
Below left is the C5 aluminum rear cradle – below right is the aluminum C6 rear cradle
Although the C5 rear cradle appears quite different from the C6 rear cradle, the four frame mounting points are identical, and the cradles are actually interchangeable between the C5 and C6 Corvettes.
And both of them may be used with our adapters.
However, there is one critical difference that builders utilizing either the C5 or the C6 IRS should be aware of. In 2005, with the advent of the C6, Chevrolet lengthened the wheelbase 1.2" (From 104.5" to 105.7".)
They accomplished this with a little tweek in the rear suspension geometry. The lower control arms and their mounts were moved enough to relocate the rear spindle 1.2" rearward. This is important to remember, especially when designing your rear frame and locating your axle centerline within your rear wheel opening.
Please note in the photo below: The 8.0" dimension is for the C5 and the 9.2" dimension is for the C6.
As you might imagine, designing and fabricating the upper locating points from scratch is extremely difficult, time consuming and expensive.
It would be a much easier process if only the common 3-axis X,Y and Z coordinates were necessary.
But since the mounting locations for the lower control arms, the upper control arms and the shocks are all on different planes, with different angles, at least five axes must be brought into play.
And remember, if the upper arms and shocks are not mounted precisely, there will be no hope of ever properly aligning the front or the rear of the vehicle.
Even with the extremely close tolerances that are required, a few shops, aftermarket manufacturers and even some home builders are now fabricating their own independent rear suspension systems utilizing many of the C5 IRS components.
As seen below, in an attempt to minimize the possibility of a bracket being positioned improperly, builders do their best to match the original C5 Corvette unibody frame when plotting the coordinates to position the upper mounts – then weld them directly to their new frames.
If it's done improperly, the problem might stay hidden until the project makes it
all the way to the alignment shop.