2021 BMW 840i xDrive Trailing Arm Replacement Cost

Trailing arms are a component which is not found on all vehicles. They may be found on passenger cars, SUV's, trucks, and vans, and they can be adapted to straight axle vehicles or vehicles with independent suspension. The purpose of the trailing arm is to prevent forward or rearward movement of the axle or control arm that they support, which results in increased handling characteristics, high speed stability, and better steering response. Whether on the rear or front of the vehicle, the trailing arm provides the axle or control arm with an additional mounting point to the frame. When a suspension concern arises, the trailing arm will likely be inspected along with other components to rule out or diagnose trailing arm failure.

Many control arms and drive axles have limited support from longitudinal movement, that is allowing the wheel to move forward and backwards in the wheel well, so trailing arms have been introduced to help solve that issue. The trailing arm is mounted in front of or behind the axle or control arm, and attaches directly to the frame. Both ends of the trailing arm allow the suspension to move up and down, but since the trailing arm is mounted perpendicular to the control arm or axle, the wheel and hub assembly is unable to move in any other direction. This allows for a high degree of stability, ensures necessary movement of the suspension system, and prevents the vehicle from wandering within the lane.

Trailing arm symptoms are similar to other suspension system failures, but are more limited in the effects they may have on a vehicle. Noises like squeaking, creaking, rattling or clunking may be heard when a bushing is worn. The vehicle may seem to shift to one side during acceleration or braking. The vehicle may wander around the lane while driving straight down the road, and, finally, the tires may experience swirling on the edges.

Noisy trailing arm bushings should be addressed at the earliest convenience. However, when a noisy bushing turns into a clunking bushing, it should be repaired right away. Also, when the vehicle begins shifting to one side during braking or accelerating, this situation becomes a safety hazard, and should be repaired immediately. Aside from loss of control, this situation will lead to misalignment of the wheels, tire wear, and possible frame damage where the trailing arm attaches.

Trailing arm replacement is not very common, in fact, the item that typically fails is not the trailing arm, but the trailing arm bushings. Trailing arms use bushings to reduce vibrations, dampen impact from bumps, and prevent contact between the trailing arm and trailing arm mount. These bushings wear out after a long service life, or a severe impact, so in lieu of a severe impact to the wheel, expect the trailing arm and bushing to last many years before replacement.

Trailing arm failure diagnosis is as simple as finding that the trailing arm is bent, cracked, or broken. This can be done in most cases by a visual inspection, and the tire associated with that trailing arm will likely show wear patterns different than other tires. If the trailing arm is found to have worn bushings, excess movement, or if it makes noise as it articulates, the bushings will likely be replaced in lieu of the trailing arm.

Replacing a trailing arm will require the vehicle to be lifted, then the axle or control arm connecting to the trailing arm will need to be supported independently of the vehicle. This will allow the trailing arm to sit in a neutral position, with no weight pushing or pulling the trailing arm in any direction. Afterwards, the trailing arm will be released at the mounting points, removed, and replaced. Finally, the bolts for the trailing arm and wheel will be tightened to proper torque specifications once they are fitted onto the vehicle, and it is time for a test drive.

When replacing the trailing arm bushings, we recommend replacing both sides at once. Even if the trailing arm bushings have failed due to hitting a pothole, the bushings on the other side will be softer, and may lead to failure of the old bushings more quickly.

Trailing arm bushings that have failed where the trailing arm connects to the frame can easily cause damage to that mounting point. If the new trailing arm and bushing will not align properly on the vehicle, or the frame is obviously damaged, the vehicle subframe or crossmember may call for replacement. In this situation it is important to have the vehicle assessed by a professional to ensure the vehicle is safe to operate.

Replacing a trailing arm requires a light amount of knowledge and basic tools. Proper lifting and supporting techniques should be adhered to, and the fasteners should be replaced and torqued to manufacturer specifications. Otherwise, this is a straightforward job, and a professional will only need to be consulted of the trailing arm mount to the frame is damaged.