The engine in your vehicle is attached to the frame of the vehicle. When the engine operates, it causes vibrations. Engine and transmission mounts are necessary to hold and support the engine and transmission, and to isolate the vibrations that happen when the engine is running. The mounts act as an insulator between the vehicle frame and the engine components.
Engine and transmission mounts are usually filled with solid rubber so that there is no direct metal on metal contact between the engine and frame of the vehicle.
To improve comfort, some vehicles have fluid-filled hydraulic mounts which absorb and dampen vibrations that would otherwise pass right through a conventional solid rubber mount. While comfort is something we all enjoy, fluid-filled mounts are more expensive than solid rubber mounts, and they can leak fluid and collapse after years of service.
Some import vehicles have electronically-controlled mounts that can alter the stiffness of the mount to cancel out harmonics at various engine speeds and load weights. These mounts can use a vacuum-actuator to change the stiffness of the mount, and some even generate their own counter shake to offset engine vibrations at various speeds.
Today, most front-wheel drive cars, SUVs, and minivans use transverse-mounted engines and transaxles. This means the engine is mounted perpendicular to the centerline of the vehicle. This style of engine mounting usually requires either three or four mounts for the engine and transaxle to be properly secured to the frame.
On rear-wheel drive cars and trucks, there is usually a pair of engine mounts on each side of the engine to support the engine, and a single mount under the back of the transmission.
Upper engine mounts are sometimes used and are often called ‘struts’ or ‘dog bones’. They prevent the engine from rocking back and forth as the vehicle accelerates and decelerates. Upper mounts usually have a rubber bushing with metal sleeves in each end. One end is attached to the engine and the other to the radiator cross member support.
Mounts deteriorate with age and mileage, so it’s not unusual to find one or more broken or collapsed mounts in older or high-mileage vehicles. If one mount has failed, chances are the other mounts are near the end of their service life and should also be replaced.
Cracked, loose, leaking, or broken mounts may allow excessive engine and transaxle movement which in turn could cause damage and misalignment of important components. Faulty engine and transmission mounts are often a cause of excessive engine noise and vibration, and can also result in clunking and banging noises when placing the transmission into gear or accelerating. Continual stretching and pressure on engine and transmission mounts will eventually take a toll.
Due to the amount of vibration an engine generates as part of its operation, engine and transmission mounts are an essential component on any vehicle. When engine mounts fail, not only will the cabin be uncomfortable for the driver and passengers, additional strain will be placed on the engine that can damage other components.
Often, excessive vibration resulting from faulty engine and transmission mounts is more noticeable at idle with the transmission engaged. If you suspect your engine and transmission mounts may need attention, have the vehicle inspected by an ASE certified technician right away.