1999 BMW 740i Engine Mount Replacement Cost

There are typically two or more engine mounts in a vehicle. Depending on the vehicle configuration, the engine will either rest on mounts bolted to the vehicle subframe, or will be suspended by mounts bolted to the vehicle's actual frame. In the case of front wheel drive vehicles, these mounts may also support the transmission from the side, and with stabilizers from above. There are several styles of mounts, ranging from solid rubber, to liquid filled. Most modern motor mounts use a liquid filled core, which is contained inside of a composite rubber insert. This allows the mount to flex as needed while still preventing the vehicle from absorbing the vibrations and noise from the engine. This composite rubber insert, also called the insulator, is encased in a metallic housing to provide a firm, stable mounting surface for the engine and transmission, and the portion that connects to the engine is inserted into the insulator and secured via bolts. This design suspends the engine by composite rubber instead of metal.

Vibration in the cabin while the engine is running can be an indication of several component failures, but when the engine is otherwise healthy, the engine mounts are suspected of failure. Not only will they create annoying vibrations and rattles, they can also create a clunk that can be felt and heard whenever the vehicle is put into drive or reverse. If not repaired, the clunking noise will begin to happen at bumps, acceleration, and deceleration, until the mount finally fails, and the engine is able to move freely of that mount. Lastly, when many modern motor mounts fail, there is normally a liquid dripping from the motor mount.