2008 Cadillac CTS: Suspension Walkaround
April 29, 2009
By now you might be able to recognize what you're seeing without me going on at length. After all, there are only so many ways to lay out a suspension.
Our 2008 Cadillac CTS has a double-wishbone setup with a high-mount upper arm, and it uses a lot of aluminum bits and pieces.
The difference between the double wishbone and double control arm designation amounts to a technicality, but I'm going with double wishbone here because the one-piece aluminum lower control arm (blue) is generally A-shaped, not L-shaped.
An earlier post of mine mentioned that our CTS has forward-mounted steering (yellow), as opposed to the CTS AWD, which does not. Our RWD CTS steers quite precisely, so it paid off.
And our CTS has very functional front brake ducts (black) that shoot air gathered from front grille openings onto the front rotors.
In this view you can see the coil over shock absorber (green). The upper end of the stabilizer link (yellow) attaches directly to the aluminum hub carrier (aka knuckle or upright) for a 1:1 motion ratio. A 1:1 ratio means they can call this a direct-acting stabilizer bar, and since the bar can give everything it's got, it can be smaller (and lighter) and still get the job done.
Here's the upper arm, with a decent amount of anti-dive geometry (yellow). The cool part is the one-piece aluminum upper mounting bracket, which also carries the upper mount for the coil-over.
That aluminum upper suspension mounting bracket bolts to the shock towers of the unibody with these four bolts (yellow). An extruded aluminum "stress bar" bolts to two of them to help make the upper end more rigid by combating the tendency of the towers to flex inward under load.
The CTS has 2-piston sliding calipers and ventilated front rotors. Calipers are almost always the product of an outside supplier, and the green circle indicates that these are made by Mando, a Hyundai-family supplier that has a big US presence and a US plant.
Here's a quick run-through on how a sliding caliper works. Sliding calipers have their pistons on one side. This one has two of them (green). When you press on the brake pedal, the pistons move in the green direction, pressing the pad against the rotor. A sliding caliper floats on pins (yellow) and the equal-and-opposite reaction means the caliper itself will slide in the yellow direction. But the caliper wraps around the other side of the rotor, where another brake pad sits (purple). The motion of the caliper in the yellow direction pulls the purple pad against the rotor. Bottom line: pistons on one side provide clamping force to pads on both sides.
Sliding caliper brake pads are really easy to service if your rotors are in good shape. All you need to do is remove one small bolt (black) and pivot the whole affair up on it's opposite partner. Here I'd remove the upper one and pivot it on the lower one, owing to the brake hose routing.
In an unrelated matter, the white arrow shows the upper stabilizer bar attachment point more clearly. The bolt has a long hex nose so you can hold it in one place with a second wrench while you tighten the main nut. Without it, the ball joint will just spin and spin and you'll never get it tight.
The CTS uses multilink suspension on the rear end. It has a one-piece y-shaped aluminum upper arm and three links. The green and purple links approximate a lower arm, though they attach to the knuckle at seperate points. The final link (white) is a toe-control link.
Here's another angle of that toe control link (yellow), and you can see that it's easily adjustable, with left and right hand threads on opposite ends so you can simply loosen the jamb nut and twist is as much as necessary.
You can see one of the four rubber rear subframe mounts and the forward-pointing trailing link (green) that we saw before.
The shock absorber mounts directly to the knuckle (white) for a 1:1 motion ratio. And, like the stabilizer bar we saw earlier, a direct-mounted shock can be smaller and still get the job done as well as a larger one that isn't direct-mounted.
Here's the rear stabilizer bar (green). It isn't direct mounted, but it's close (yellow). The motion ratio looks to be about 0.9:1 or thereabouts.
There's another subframe bushing (purple) and the parking brake cable (white). This has a drum parking brake packaged within the "hat" of the rotor. What do they call that? A drum-in-hat parking brake, of course.
Here's the rear brake caliper. It's a single-pistion (green) sliding caliper, a very common and effective design. Fixed-piston calipers may look great through the wheels, and they certainly have benefits for track use, but sliding calipers can certainly get the job done. Here GM put their money where it can do the most good: nice, deep ventilated rear rotors.
Here's a trick that racers have used for a long time, yet you hardly every see it on passenger cars. The wheel studs are elongated, the first few threads have been machined away and the ends are tapered. This makes it easy to start the lugs quickly without cross-threading them. The lug nuts themselves have to be longer in order to hide it all, something racers don't worry about.
For the record, the wheel and tire assemblies weighed 52 pounds. The rims are 18 x 8.5 inches with a 48 mm offset.
Dan Edmunds, Director of Vehicle Testing @ 28,255 miles