A4: Suspension & Steering (Sample Test)

When evaluating a shock absorber for potential replacement due to a fluid leak, a common method used is the bounce test. This test involves pressing down firmly on each corner of the vehicle and watching how it rebounds. If the shock absorber is leaking or malfunctioning, the vehicle may bounce excessively or fail to settle quickly, indicating insufficient dampening. Such results suggest that the shock absorber is no longer performing effectively and should likely be replaced.

Technician A is correct in stating that a broken center bolt on the left rear leaf spring can impact the vehicle’s thrust angle. The thrust angle refers to the angle between the vehicle’s centerline and the direction the rear wheels are pointing. A broken center bolt can cause the rear axle to shift, altering this angle and affecting alignment, which in turn may lead to instability, poor handling, and uneven tire wear.

Technician B is also correct that an incorrect thrust angle can interfere with steering wheel centering. When the thrust angle is out of specification, the vehicle may pull to one side, forcing the driver to make constant steering corrections. Over time, this can contribute to excessive wear on steering components and misalignment of the steering wheel.

Technician A is correct in stating that a faulty jounce bumper can cause a vehicle to fail the jounce test. However, it’s important to note that other issues—such as a worn shock absorber or a bent control arm—can also lead to failure during the jounce test by affecting suspension movement and ride quality.

Technician B is also correct that the lower ball joint must be removed to replace the jounce bumper on a Short-Long Arm (SLA) suspension system. That said, removing the lower ball joint isn’t solely for jounce bumper replacement—it may also be necessary if the ball joint itself is worn or if the control arm is damaged and needs servicing or replacement.

A steering U-joint coupling is not a typical cause of a vehicle pulling steadily to the left. A consistent pull in one direction is more commonly linked to issues such as uneven tire pressure, wheel alignment problems, or faults in the suspension or steering geometry. Misaligned camber or caster angles can also lead to directional instability and uneven handling.

The steering U-joint coupling, while essential for transferring input from the steering wheel to the steering rack or gearbox, primarily affects steering responsiveness and feel. If it becomes worn or damaged, it may cause play or stiffness in the steering, but it does not generally cause the vehicle to pull to one side.

Excessive positive camber can lead to premature wear on the outer edge of a tire’s tread, while too much negative camber typically causes wear on the inner edge. Positive caster, when excessive, may contribute to wheel shimmy, although such shimmy is more often linked to worn or loose steering components. On the other hand, negative caster is sometimes used in heavy-duty vehicles to make steering easier, particularly when the vehicle is carrying substantial loads, though it can reduce straight-line stability. Proper alignment of camber and caster angles is essential for balanced tire wear and optimal vehicle handling.

A dry park test is a straightforward inspection technique used to detect issues in a vehicle’s steering system. Performed with the engine off and the vehicle stationary, the test involves turning the steering wheel back and forth while technicians observe the steering components. The goal is to identify any excessive play, looseness, or unusual movement in the steering linkage, which could signal worn or damaged parts. Technicians also listen for abnormal noises or vibrations and may visually inspect joints and connections for signs of wear, damage, or deterioration that could compromise steering performance.

When unloading ball joints on a front suspension system where the coil spring is positioned between the frame and the lower control arm, it is crucial to place a safety stand under the lower control arm. This precaution is necessary because, once the ball joints are unloaded, the suspension can suddenly drop and the lower control arm may swing downward. Without proper support, the coil spring can dislodge or be ejected forcefully, posing a serious safety risk.

To prevent injury and ensure a controlled release of tension, the safety stand must be positioned securely under the lower control arm to support the suspension’s weight. It should be placed in a way that provides stable support without obstructing the arm’s movement. While components like ride height and shock absorbers are important for the overall function and safety of the suspension system, they are not directly involved in the process of unloading ball joints in this setup.

Technician B is more likely to be correct in this scenario. If a technician has already placed multiple weights around the rim and the tire still cannot be balanced, simply adding more weights is unlikely to resolve the issue and may actually introduce new problems, such as vibration or uneven tire wear. Instead, Technician B’s suggestion to dismount the tire and inspect the inside for liquid or debris is a more effective and logical next step. Foreign material or fluid inside the tire can create an internal imbalance that external weights cannot correct. By examining the interior of the tire, the technician can identify the root cause of the imbalance and take the necessary actions to fix it properly.

The airbag solenoid functions as a two-way valve that can control the inflation and deflation of the airbag. When energized, the solenoid opens to allow air to flow into the airbag; when de-energized, it closes to prevent airflow, effectively sealing the system. This solenoid is managed by the airbag control module (ACM), which monitors inputs from various sensors—including the crash sensor, seat belt sensor, and occupant weight sensor—to determine the appropriate response.

In the event of a collision, the ACM sends a signal to energize the solenoid, triggering airbag inflation to protect vehicle occupants. Conversely, if deployment is not warranted, the ACM will keep the solenoid de-energized to prevent unnecessary inflation. Therefore, both technicians are correct: the airbag solenoid can be used to either inflate or deflate the airbag, depending on the real-time data and safety requirements evaluated by the ACM.

The issue is likely caused by either a worn relay rod ball socket or an incorrectly set tie rod adjusting sleeve. A worn relay rod ball socket can create excessive play in the steering linkage, leading to poor handling and alignment issues. Similarly, an incorrect tie rod adjustment can prevent proper toe alignment, affecting steering response and tire wear. Both components should be carefully inspected to determine the root cause of the problem.