COMMON SUSPENSION PROBLEMS
Passenger vehicles can often start to show signs of suspension fatigue or failure after only a few years, and this is particularly true of vehicles which are used off-road or for load-carrying or towing.
Sometimes, suspension issues can cause a vehicle to fail its MOT inspection – most commonly due to uneven ride height, corrosion, leaks or other serious issues. However, just because your suspension meets basic safety requirements, it is not necessarily in good order. When the front or rear of a vehicle sags evenly, worn out springs are often the cause. Uneven ride height from side-to-side is commonly due to broken or sagging springs.
Shock Absorber Problems
Shock absorbers are installed to control the travel and rebound of other suspension components, and typically contain oil and gas. Over time, the oil can break down or foam, and performance becomes reduced. Seals can also fail, leading to leakage and eventual collapse.
With your 4WD or truck parked on level ground, bounce each corner of the vehicle several times and then allow it to settle. Spring travel should stop in a controlled fashion, usually after no more than one movement cycle. Continued movement is often a sign of shock absorber failure.
Leaf Spring Problems
If you suspect leaf spring issues, firstly check for broken or missing leaves. Worn-out leaf springs tend to cause a reduction in ride height as the spring packs become flatter, so check whether the vehicle is sitting level. Flattened leaf springs will be more prone to ‘bottoming out’ over bumps and may not perform correctly under normal driving conditions.
When leaf springs become worn, visible cracks are possible and corrosion is common. Spring bushes can become brittle and crack or disintegrate, and ride quality suffers.
Coil Spring Problems
Similarly, worn-out coil springs can cause a reduction in ride height, less resistance against bumps, and reduced load-carrying capability. Due to their construction from thinner materials, coil springs are more prone to thinning and breakage.
Symptoms of broken springs become more noticeable with the addition of even relatively small loads, and may result in unusual noises in operation. This can lead to handling problems, accelerated tyre wear, and even loss of control under heavy acceleration or braking.
Torsion Bar Problems
Torsion Bars consist of a steel rod or bar, attached at one end to the vehicle’s wishbone, which twists along its axis when the wishbone travels up and down. The other end is fixed in place and does not twist. When a wheel contacts a bump or dip, the torsion bar twists to absorb the motion, after which it ‘unwinds’ and returns to its normal position. Torsion bars are typically mounted front-to-rear on the vehicle, allowing greater wheel travel on 4WD vehicles and trucks.
This type of configuration is space-efficient, allowing flexible location of axles and other components and ride height adjustment by tensioning or ‘cranking’ the torsion bars within certain parameters.
However, they can more easily be damaged by contact with objects in the vehicle’s path, so it is important to visually inspect them for damage and replace if needed.
As with coil and leaf springs, sagging ride height is the most likely indicator of worn torsion bars. Harsher ride quality is also common, as torsion bars lose their range of torsion and become more brittle. Broken torsion bars tend to cause serious ride issues and accompanying noise.
Height Adjustable Suspension
Some vehicles, typically premium 4WD models such as Toyota Land Cruisers or Range Rovers, can be factory-fitted with complex suspension setups such as Toyota’s Kinetic Dynamic Suspension System (KDSS) or Air Ride suspension. These systems use compressed air or fluid-filled reservoirs to raise or lower the vehicle, either on demand or automatically.
Unfortunately, experience has shown that once these systems start to age, they can become unreliable and are often very costly to fix. In some cases, aftermarket solutions are available to replace these systems with conventional suspension setups to allow the vehicle to remain serviceable. Whilst it is difficult to offer general diagnostic advice given the diverse nature of different manufacturers’ systems, common issues include loss of ride height, leakage, or inoperable height adjustment selection.
Replacing Suspension Components
If your vehicle’s suspension is worn to the point where components have begun to fail, you should consider the condition and suitability of the remaining springs, shocks or torsion bars. Now could be a good time to invest in a quality replacement suspension system, which will last for a long time and improve comfort and safety. When you consider the level of use and abuse which these components undergo, it is easy to understand the benefits of installing an integrated replacement system.