Vehicle Suspension Components

Control Arm Overview and Functionality

  • Definition and Location:

    • Control arms function as locators for the wheel and its associated components in relation to the vehicle chassis.

    • They are utilized in independent suspension systems.

    • They are found on both front and rear applications.

  • Acceleration Mechanics and Force Transfer:

    • When a vehicle accelerates from a stop, the rear wheels rotate in a forward direction.

    • Simultaneously, the axle attempts to twist and lift due to rotational torque.

    • The control arm transfers the twisting motion of the axle directly to the frame.

    • Controlling this twisting motion propels the vehicle in the direction the wheels are traveling.

  • Bushing Construction and Function:

    • Control arms use bushings to connect to the frame and an axle assembly.

    • Rubber compound bushings absorb shock caused by sudden movements of the suspension system.

    • Bushings establish connection points that eliminate direct metal-to-metal contact.

    • Eliminating metal-to-metal contact reduces the transfer of noises and vibrations into the vehicle.

    • Bushings allow the control arm assembly to move vertically to help compensate for bumps in the road.

Four-Link Triangulated Suspension Systems and Alignment Adjustments

  • Four-Link Triangulated Suspension System Configuration:

    • Control arms are used in a four-link triangulated suspension system to reduce lateral (side-to-side) movement of an axle assembly.

    • Top Control Arms: Typically attach to the top of an axle assembly and extend forward to the frame, forming a V shape.

    • Lower Control Arms: Mounted below the axle and extend to the frame parallel to the frame rail.

  • Alignment Adjustments and Eccentric Bolts:

    • Control arms can be used as an adjustable link to assist with front or rear suspension system alignment.

    • Changes are typically made using an adjustment cam, which is also called an eccentric bolt.

    • Adjustment Cam Structure: A round disc that utilizes an offset hole.

    • Adjustment Mechanism:

    • A bolt slides through the offset hole and cam to connect to the other cam disc on the opposite side of the control arm.

    • Rotating the bolt moves the control arm up or down, or in or out.

    • Movement of the control arm alters the suspension alignment angles accordingly.

Trailing Arms Construction and Mechanics

  • Trailing Arm Definition and Mounting:

    • A trailing arm is defined as any link positioned in front of the axle and located between the chassis or frame.

    • Frame/Chassis Mounting: Mounted to the frame or chassis with a bushing and bolt.

    • Axle/Knuckle Mounting: The opposite end is mounted either with a similar bushing and bolt configuration or is rigidly mounted with bolts to the axle or knuckle.

  • Forces and Motion Control:

    • Trailing arms counter front-to-rear forces on either a driven or non-driven rear axle.

    • They keep the driven axle from twisting under acceleration or braking.

    • Because the trailing arm provides a rigid link from the axle to the frame, it eliminates most of the transfer of front-to-rear motion.

    • Bushings absorb some motion to help reduce noise and vibrations.

  • Material and Structural Shapes:

    • Trailing arms are generally made from steel to provide necessary strength.

    • Constructed in either a square shape or as a cylindrical rod.

    • High structural strength is required to keep the axle in place under acceleration and braking forces.

Four-Link Parallel Systems and Suspension Variations

  • Four-Link Parallel Systems:

    • Trailing arms generally mount to both the top and bottom of the axle.

    • They extend forward at a 90-degree angle from the axle and run parallel to the vehicle centerline.

    • The trailing arms mount to the frame using bushings and bolts.

  • Torque Arm Variation:

    • The torque arm is a variation that replaces the upper trailing arms.

    • Attachment: Bolts to the differential housing, runs parallel to the drive shaft, and connects to the transmission or the transmission cross member with a bracket.

    • Function: Provides additional assistance to prevent axle housing rotation under acceleration and braking.

  • Strut Rods:

    • Strut rods are used in the suspension system when the lower control arm is narrow or built in an I-shape.

    • Function: Provides stability and strength to a narrow control arm.

    • Attachment: Attaches with a bracket to the frame and connects to the control arm with bolts or rivets.

    • Vibration Damping: Generally feature bushings at the mounting points to prevent the transfer of noise and vibration into the vehicle.