Suspension components by themselves can't shake simply for the fact that they don't rotate. However, they can give the wheels the opportunity to wobble.
As a vehicle rolls down the highway its wheels—particularly the front on a rear-drive car—encounter an intense amount of resistance. Just one worn component can let the suspension deflect out of alignment. If the suspension deflects enough to let the geometry enter an unfavorable range then a wobble may follow.
Last but far from least, driveshafts, since they spin several times faster than the drive wheels they're particularly capable of vibrating. We'll let Steve Raymond at Dynotech Engineering Services explain a few essential things. And he's well versed; when the Big Three encounter persistent vibration issues they hire Dynotech to find and solve them.
"You want equal and opposite," he instructs. "If your tailshaft points down 2 degrees then your pinion should point up 2 degrees so effectively they run parallel." Why? Universal joints at an angle don't spin in a circle; they follow an ellipse that makes them speed up and slow down at various points. "If the joints are phased correctly on the shaft then one joint will accelerate as the other joint decelerates and the two forces will cancel each other.
But don't confuse parallel with straight line. "Set your U-joint angles at a minimum of 0.5 degree to 3 degrees," he says. "If the joint is at 0 degrees then (it) won't articulate and the needle bearings won't roll. That will purge the grease out of the caps and wear the bearings. But when they roll they distribute grease through the cap. Without that little bit of movement the joints will run hot and wear out prematurely. A worn joint can introduce a vibration."
Here's a tip if your engine vibrates at certain speeds even when the car sits still: disassemble assemblies (like a torque converter from a flexplate), rotate one side (like the torque converter), and reassemble. You may do a reasonable job balancing each of the components but small imbalances always remain," he says. "So you have to prevent those small imbalances from adding up at one angle." By rotating one part 180 degrees the imbalances may cancel out each other.
9. Ideally, manufacturers replace square tires; however, some specialty tires are notorious for roundness issues. In those cases find someone like my pal Bill Ross who trues tires. It takes a bit of life off a tire but what good is a life spent wobbling?
10. This Hunter model illustrates toe-in. If your car shakes despite all other efforts then play with toe. Just don't go too far and remember that toe-out usually makes a car dart (it wants to turn in all the time).
11. Wheel Centerline Caster Angle Trail We amplified the dimensions but this illustrates how the tire centerline (yellow) actually "trails" the point where the steering axis (red) intersects the ground. Less trail makes a car feel lively but too little makes it wander. More trail makes it stable but too much makes the steering feel dead and can induce a wobble.
12. Consider every wear point a potential culprit in a persistent wobble issue. Worn kingpins, ball joints, bushings, tie-rod ends, idler arms, strut rods, and even steering gears can let the geometry slip into the wobble zone.
13. This is a steering damper. Though it can damp small oscillations that cause wobbles that is not its job. It exists to take the edge off of the small impacts amplified by the gear lash in older steering boxes before they reach your hands.
14. Joints work best with at least 0.5 degree but no more than 3 degrees misalignment. For a one-piece driveshaft on a road car set the pinion angle at the exact inverse angle of the tailshaft. So if the tailshaft points down 2 degrees then point the pinion up 2 degrees.