Mercedes-Benz SL320 Suspension Shock or Strut Replacement Cost

There are many components that make up the steering and suspension systems on a vehicle. The wheel is bolted to a wheel hub that turns inside bearings set in the steering knuckle. The knuckle, in turn, is connected at the bottom to a moving bracket called the lower control arm, and at the top to the strut and possibly an upper control arm. The steering gear is attached to the knuckle by way of the tie rods so that when the steering wheel is turned, the knuckle turns with it, rotating on the lower control arm and the upper strut mount. The strut assembly, widely known as a MacPherson strut, is made up of a special shock absorber, a coil spring, and the rotating upper strut mount and bearing assembly. Additionally, vehicles using shock absorbers instead of struts will have the shock mounted to the chassis and the lower control arm. This allows the shock absorber to moderate the movement of the coil spring, preventing the vehicle from bouncing up and down indefinitely.

Because the suspension struts and shocks control the entire weight of the vehicle, they can wear out over time. The shock absorber is usually the first to go. When this happens, the ride quality becomes "bouncy" or loose, and the vehicle's ability when cornering in a turn diminishes. Oil may be seen leaking from some types of struts and shock absorbers. Also, since the upper mount is constantly being turned or compressed, it will eventually break down and squeak of clunk over bumps and during turns. For struts, a clicking or growling noise when turning can indicate a worn bearing inside the upper strut mount, and a squeaking sound when the steering wheel is turned can mean that the rubber bushings in the mount are decaying as mentioned. Also for struts, the coil spring can break and cause a loud clunking sound when turning or when going over bumps.

Suspension struts and shocks may or may not fail all at once. And each of its members do not fail equally. The decline is gradual and may be difficult to notice at first. A vehicle with worn struts or shocks can be driven, but the ride quality will be diminished. More importantly, the vehicle's handling will be compromised. A car's ability to remain level while turning, with traction spread between all four wheels, is dependent on the struts or shocks, and as the condition of the suspension struts and shocks worsens, the ability of the suspension to perform properly also worsens - especially in an emergency situation. Loss of control and chance of vehicle rollover can be the result of severely worn struts and shocks. If a strut or shock absorber shaft is broken or bent, the vehicle should not be driven until it can be replaced.

There is no replacement schedule for most suspension struts and shocks, through many vehicles will need to have them changed at some point. Rough driving habits may shorten the life of these parts. Struts and shocks may need to be replaced anywhere between 50k and 100k miles. If at any time the struts or shocks are leaking, broken, or damaged, they should be replaced immediately. Lastly, they should always be replaced as pairs. In other words, if one front shock or strut is replaced, the other front shock or strut should be replaced as well.

If the vehicle has excessive play in the suspension - if the vehicle bounces easily up and down - the suspension shocks or struts are likely worn. Many times, a strut is diagnosed when a technician is replacing other related parts. A damaged strut may also be discovered during a four wheel alignment. In doubt, a technician will use body weight to bounce the vehicle up and down on each corner, and if the amount of residual movement up and down is excessive, the shocks or struts are worn. Extremely worn shocks and struts are more than obvious while driving, as the vehicle will float up and down after bumps, often bottom out, and lean excessively through turns.

To change a suspension strut, a technician first needs to lift and support the vehicle with a hoist (or a jack and jack stands) and remove the front wheel. The brake caliper and rotor are removed and the sway bar link is disconnected. The technician then disconnects the strut from the steering knuckle and from the strut tower to remove it from the vehicle. If the entire strut assembly is being replaced, installation is relatively simple. On the other hand, it is common to reuse the coil spring from the old assembly. In this case, the worn strut will need to be compressed and disassembled, and the new strut will need to be put together before it is installed. On the other hand, shocks are much easier to change. Most often, removal of the wheel is sufficient to allow the upper and lower mounting bolts to be removed. Once removed, the new shock mount and shock are installed. Once the wheel is torqued, the process is repeated on at least one more shock.

RepairPal recommends replacing the suspension struts or shocks in pairs, left and right. The ride quality and performance of the vehicle will be significantly altered if the struts and shocks do not match in type and quality. Prior to replacement of shocks or struts, a full inspection of the steering and suspension should be performed to identify any other needed repairs. This will cut down the labor costs when compared to replacing the worn parts separately. Also, we recommend a four-wheel alignment when struts are replaced. New struts can change the vehicle's ride height, which will change the wheel alignment.

If the suspension shocks or struts are damaged, the wheel alignment of the vehicle will be impaired. During replacement, it may be necessary to compress a strut and spring assembly, unlike a shock absorber. This involves compressing the coil spring so that the strut assembly can be disassembled. From the time that the old strut is disassembled to the time the new strut is assembled, the compressed coil spring is extremely dangerous. If the spring slips from the spring compressor (used to apply tension to the spring), it could cause serious injury. Also, the vehicle needs to be safely lifted and supported off the ground to complete this repair.

Replacing an entire suspension strut assembly as a unit could be considered an intermediate DIY repair. On the other hand, if the coil spring is to be transferred from the old strut to the new strut, or if the old spring is broken and in need of replacement, this repair should only be attempted by an advanced DIYer, or left to a professional technician. However, since shock absorbers are typically easier and safer to replace, most DIY mechanics will have an easy time replacing these. That is if proper lifting and supporting of the vehicle is understood.