Body mount bushings are cushions made of rubber or polyester that are placed between the body and frame of a vehicle. Anywhere from six to twelve bushings might be used to separate the body from the frame.
Most vehicles made prior to the mid nineteen nineties featured body-on-frame design. With this design, the engine, transmission, suspension, and steering are all connected to the frame. The body structure, separate from the frame, is bolted on top, with body mount bushings inserted at each mounting point.
Although many trucks still come with body-on-frame construction, most modern passenger vehicles are constructed of what is known as a “unibody” design. The entire body of the vehicle is made up of a collection of steel panels that are welded together into a single shell. The engine, transmission, suspension, and steering components are bolted directly to the body. The only part that resembles a traditional frame is the engine cradle, or “subframe”, and possibly a rear suspension crossmember.
Body mount bushings are used to isolate the body from the frame on a traditional body-on-frame vehicle, and to isolate the subframe on a unibody vehicle.
Body mount bushings are subject to a good deal of stress from the weight of a vehicle and the vibrations and torque applied by the drivetrain and suspension. Over time, they tend to wear out and break down, especially on older vehicles.
The signs of a bad body mount bushing can depend on whether the vehicle is a body-on-frame or a unibody design. In general, your vehicle might need body mount bushings replaced if you notice one or more of the following:
To replace body mount bushings, a technician must be able to separate the body from the frame. The weight of the body must be lifted off of the frame in order to create space to remove the body mount bushings. To do this, the technician will remove the body mount fasteners, disconnect any cables, wires, lines, or other components necessary for separation to occur, and raise the body on a hoist. At this point, the old bushings are removed and new bushings are inserted. The vehicle is lowered in place, aligned, and refastened.
The process is a bit different for a unibody vehicle. To replace the bushings in a subframe, the technician must be able to support the weight of the engine and transmission or transaxle independent of the body. That way, the subframe can be disconnected and removed completely from beneath the vehicle. This also requires raising the vehicle on a hoist. Some vehicles require that the engine be lowered with the subframe, although this is less common. With the subframe free of the body structure, the old bushings are removed and replaced with new bushings.
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