The first concern is with the control arm. A common problem when this is done by a do-it-yourselfer or an inexperienced mechanic is they tighten the pivot bolts while the car is still on the hoist or jacked up. That tightens the bushings with the arm hanging down, then, when the car is lowered onto the tires and the arm moves up to its normal position, the bushings are clamped in a permanent twist. That greatly reduces their life and will tear the rubber from the metal sleeves. Once they're torn free, the constant movement from bouncing down the road grinds the rubber away until the clunking noise is heard.
Double-check the nut on the ball joint's stud. If a small piece of dirt or debris got overlooked on the stud, it will prevent it from being fully-seated when the nut is torqued to specs. Once that debris grinds away, the stud will be loose. That will cause the tapered hole and the stud to wear away and become deformed. The only proper repair for that is to replace the spindle and replace the ball joint again.
Since this is speed-related, the best suspect is loose lug nuts. It is critical they be tightened to specs with a click-type torque wrench. Also, no grease should be used on the studs. Most import cars come with anodized studs. Those will have a silver, light yellow, or light blue color. That electroplated coating is a lubricant, but it will be eaten away by grease. Some people put a big wad of grease on the studs, then run the nuts on with air tools. That causes the grease to build up ahead of the nuts, then it gets flung out onto the tapered mating surface, and then it gets stuck between the nut and the wheel. That mating surface must remain perfectly dry because it's the friction that keeps the nuts tight.
If the lug nuts are not fully tightened to specs, they're going to work loose. Once that happens, the mating surfaces will be ground away and the nuts will never stay tight after that. The proper repair is to replace the wheel and all the nuts.
When the lug nuts are over-tightened, the threads can peel and become wedged. Most commonly the nuts will remain tight, but those peeled threads will cause the nut to spin and not come off the stud the next time someone tries to remove them. This is where the mechanic gets blamed unfairly when the damage was caused months or years ago by the previous person who installed the wheels.
Run the engine, in gear, on a hoist or with the front wheels jacked up off the ground, then watch the brake caliper to see if it's moving left and right. If it is, there's two common causes, and that can cause a knocking noise that is speed-related. If the new rotors are Chinese, and they're about three months old, they likely are warped. A simple machining will solve the problem permanently. When we make parts from cast iron, we set them aside for 90 days to age before they get their final machining. When the Chinese make cast iron rotors, the cast 'em, machine 'em, pack 'em, and ship them, then they age on your car. Warping is common, and that causes the caliper to walk back and forth per each wheel revolution. When there's worn spots on the pads' mounting surfaces, the pads can catch on them as they walk back and forth, and that makes a clicking or clunking noise. Most commonly that is heard when braking as that puts a force on the pads that makes them resist walking out of those worn spots, but it is possible to hear that even when not applying the brakes.
The same thing can happen when a piece of rust or scale breaks off and falls between the brake rotor and its mounting surface on the hub. When reusing old rotors, you also have to check for rust build-up on the backside of the rotor. Corrosion on the hub, around the center hole of the rotor can prevent a new or an old rotor from sitting squarely on the hub. Even if the lug nuts are tightened properly to specs, once that corrosion grinds away, the rotor and wheel will be loose.
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Tuesday, February 6th, 2018 AT 2:09 PM
