Motor mounts: what are they and what do they do?
Essentially, motor mounts are typically made of rubber or a fluid-filled rubber that are bonded to metal brackets that bolt to the engine and frame of the vehicle. They are designed as insulators that support, hang, or cradle the engine and transmission assemblies.
Most vehicles have two to four engine mounts and one or two transmission mounts depending on the layout. Older vehicles typically use solid rubber mounts. Many newer vehicles use hydraulic mounts, fluid-filled chambers that provide better vibration damping at idle and low speeds, where engine shake is most noticeable in the passenger compartment.
How motor mounts fail
Over time the rubber can deteriorate, crack, split, harden, compress, and leak fluid. This reduces its ability to insulate engine vibrations and engine torque.
Heat is the main enemy. Repeated heating and cooling cycles cause rubber to harden and lose elasticity. Fluid-filled mounts can develop leaks, leaving the chamber empty and eliminating their damping function entirely. A collapsed or broken mount does not always look obvious from above. The failure is often inside the rubber where you cannot see it.
What worn mounts allow to happen
When a mount no longer holds the engine firmly, the powertrain is free to move more than it should under load. The resulting factors are potential misalignment of axle shafts, drivelines, and interference with rotating versus stationary components.
Under hard acceleration or when engaging drive or reverse from a stop, a broken mount can allow the engine to torque far enough to contact brake lines, power steering hoses, or the firewall. That contact can cause damage to components that have nothing to do with the mount itself.
Warning signs of worn motor mounts
Some of the symptoms associated with worn motor mounts are:
- Increased vibration felt through the floor, seat, or steering wheel at idle
- Clunking or thudding noises when shifting from park into drive or reverse
- Excessive engine movement visible under the hood during acceleration
- A "bump" sensation when the transmission engages
- Vibration that worsens at certain RPM ranges
If you are experiencing some of these symptoms, we recommend having an inspection done by a qualified automotive technician. A technician can observe engine movement directly on a lift and confirm whether the mounts are the source.
Happy Motoring!