Changing Motor Mounts

THUNK upon acceleration can be unnerving. It can also foreshadow an expensive fix if not diagnosed and corrected before serious damage is done.


One of the most likely places to look for throttle-induced noises is at the joints between the transmission and wheels. U-joints and CV-joints have finite service lives and are designed as weak links in the driveline—they're cheaper and easier to replace than gear-train parts.

Diagnosis Over time, the mount's flexible part figuratively becomes arthritic, losing its absorptive traits.
If the driveline joints pass muster and the problem still exists, zero in on the motor mounts. These mounts are designed to flex and absorb a certain amount of vibration inherent in any running engine. Over time, the mount's flexible part figuratively becomes arthritic, losing its absorptive its. In more extreme cases, the mount becomes fractured. This can allow the engine to literally clunk around under the hood, rotating under acceleration and other weight-transfer conditions. This engine movement transfers additional stress downstream to other driveline components. In worst-case scenarios, abrupt acceleration or braking can cause worn-out mounts to fail, sending the engine into the radiator or other places. Fan clicks against the radiator shroud is another telltale sign of bad motor mounts.


Motor-mount inspection isn't always easy. The typical mount combines metal mounting surfaces with hard rubber or polyurethane sandwiched in between. This flexible interior substance degrades over age, but even cracked rubber or urethane isn't always detectable to the naked eye. (Black rubber in concealed areas often doesn't reveal the true state of its health.)


To check motor mounts, consult a service manual for proper procedures for your vehicle. (Obviously, transversely mounted engines are secured differently than longitudinal ones.) The procedure often requires slightly elevating the engine to take its weight off the mounts, something that shouldn't be attempted by the ill-equipped or faint of heart.