Motormounts are not a very glamorous product, but they do have an importantfunction:They support the engine and transmission, and dampen noise and vibration.The mounts isolate the engine and transmission from the chassis sovibrationsand noise are not transmitted to the rest of the vehicle.Onsome front-wheel-drive cars, upper mounts (torque struts) also control the foreandaft movements of the engine during acceleration.Mostmotor mounts are relatively simple in design and consist only of Reducer accessories metal attachmentplates and large rubber insulator blocks. But, some vehicles have “hydraulic” or “hydro-mounts” withhollow chambers filled with glycol or hydraulic fluid.Hydro-mountsact like a jelly-filled donut to absorb vibrations that would otherwise betransmitted to the chassis.

Hydro-mounts are often used with four-cylinder andV6 engines that don’t idle as smoothly as a V8, and in luxury vehicles where motorist***pect less noise and vibration. Some hydro-mounts even have internal valvingand/or a solenoid to change the dampening characteristics at different rpm tobetter tune out unwanted vibrations. These are called “switchable” hydraulic mountsor “electronic” mounts.Mountinga Diagnostic AttackWhena motor or transmission mount fails, one of several things can happen. If therubber separates or delaminates from the steel, themount can break. The design of the mount usually prevents the engine fromfalling out of the car, but it can’t keep the engine from twistingor rocking when the vehicle accelerates or is under load.Thiscan produce thumping and rattling noises, as well as overstressing componentssuch as radiator and heater hoses, wiring connectorsand the exhaust system.

In rear-wheel-drive applications that have anengine-driven fan, a broken mount may allow the fanto hit the radiator or shroud. Drive belts or pulleys may also be forced to rubagainst other components if clearances are tight.Abroken or loose motor mount in a front-wheel-drive application can be even moreserious because it may allow engine movements thatinterfere with the throttle or shift linkage. Excessive fore and aft rocking ofa transverse-mounted engine also can lead to exhaust leakswhere the head pipe joins the manifold, or cause the head pipe itself to fail.If the broken mount is an end mount, it may also contributeto a torque steer condition and cause accelerated wear or separation of theinner CV joints on one or both halfshafts.Themotor mounts are seldom checked unless there is an obvious problem, and theymay even be overlooked if the engine or transmissionis being replaced.