By Delphi Technologies
know that wishbones, ball joints and link stabilizers are all key when it comes
to servicing steering and suspension, but what about the top strut mount? Perhaps
the unsung hero of any system, it helps to cushion noise and vibration, whilst
also acting as a steering pivot for a smooth and responsive ride. Since any
wear or tear to this part can negatively affect vehicle handling, and in turn,
safety, it’s important to know how to service it. With the following advice
from Delphi Technologies you’ll know why it fails, what to look out for and how
to replace it, if and when it does…so on your next steering job you can show
off your new-found strut mount expertise.
What is a strut mount?
Fitted on cars equipped with Macpherson type struts, the top strut mount, attaches the top of the strut to the vehicle’s chassis. Its purpose, however, extends far beyond a simple mount. Indeed, the top strut mount has two main roles; it insulates the strut from the vehicle, reducing both noise and vibration. Many front strut mounts also contain a bearing which acts as a steering pivot – so as you turn the steering wheel from left to right and vice versa, the strut pivots on the strut mount, controlling the angle and alignment of the wheels.
Why it fails?
Although top strut mounts are designed to last, they are subject to significant stress day in, day out. Together with the bearing and coil spring they hold the full weight of the vehicle. They are also constantly moving – a typical strut will endure millions of cycles during its lifetime – up to 1750 times for every mile driven on a normal road surface – this constant up and down movement, which is exacerbated by potholes, bumps and kerb strikes, pushes and pulls at the mount causing wear overtime. In addition, environmental factors such as ice, water, salt spray, humidity and temperature changes can all cause damage.
Symptoms of a faulty strut mount
Like most other parts, there are a few tell-tale signs. So, if your customer complains of any of the following, the top strut mount could be at fault:
- Abnormal noises coming from the steering and suspension system i.e. clunking when driving over bumps or squeaking when maneuvering at low speed
- Premature and/or uneven tyre wear
- Accelerated wear of shock absorbers
- Excessive vibration
- Poor wheel/tyre alignment
- Poor steering return
As well as these common symptoms, a good visual inspection will help to identify possible wear or damage. Look for any signs of corrosion, cracks or tears in the rubber, separation from the metal and excessive movement in the strut assembly. Also check the steering pivot to ensure smooth and free rotation.
When to replace?
Although not part of the routine service schedule, you should regularly check the top strut mounts, and where necessary, replace in pairs – left and right sides – as soon as possible. As well as affecting steering response and driver comfort, worn or damaged top strut mounts can have a knock-on effect on other parts of the steering and suspension system such as shock absorbers and tyres, accelerating wear and causing unnecessary expense for the vehicle owner.
Also, because the top strut mount is essentially a low-cost part, in what is often a very labour intensive process, it makes sense to fit news ones whenever you’re replacing the struts. Either way, in most cases, you’ll have to remove the strut and decompress the coil spring, so it could save you from having to do the same job twice.
Why replace in pairs?
Because top strut mounts will typically endure the same number of miles and road conditions, chances are if one side is worn, the other will be too. Its therefore advisable to replace in pairs – left and right side. Doing this will ensure their performance is evenly matched across the axle for a balanced ride height and equally responsive steering and handling. An imbalance on either side, could impact both chassis and wheel movement, ultimately compromising the vehicle’s handling.
How-to replace a top strut mount
Top strut mount replacement can be a lengthy process, but by following the best practice advice below, Delphi Technologies can help to make it as seamless and ‘pain-free’ as possible:
To start, remove the plastic cover over the plenham chamber. Loosen the wheel nuts slightly before raising the vehicle. If you have an air impact gun you can skip this step – Just remember not to use the impact gun on a locking wheel nut.
Securely support and raise the vehicle to the appropriate height. Then remove the wheel nuts and wheel. If needed, remove the brake line support.
Remove the lower clamp bolt holding the strut to the steering knuckle and remove the strut from the hub.
Lower the vehicle to a suitable height to access the strut mount bolts.
Unscrew the strut top bolts, ensuring you’re supporting the strut at the same time. Do not loosen the centre bolt at this stage as this will release the high-tension spring. Then remove the strut.
Note that the suspension spring is compressed and has significant stored up energy which could cause serious injury if released. To prevent this, you’ll need to securely and safely clamp the spring. This will hold the tension in the spring, preventing any nasty accidents, and create enough play so that you can remove the strut mount.
Using a spring compressor, compress the spring until it is released from the seat of the suspension strut mount. When safe to do so, unscrew the nut from the top and remove the strut mount holding the centre of the strut with an Allen key.
You can now install the new strut mount top. First fit the bearing, ensuring the surface is clean, then mount. Note, the top of the strut maybe keyed and you’ll want to match that up with the key on the new strut mount.
Screw on the top mount nut but do not tighten fully until the strut is fitted back in the vehicle. The spring tensioner can now be released, and the assembly removed.
Position the assembly back into the strut tower and replace and tighten the strut mount bolts.
Raise the vehicle again – you can now tighten the lower bolts to vehicle manufacturers specifications. If you had to remove any suspension components, then don’t torque them up, until the vehicle has been lowered and the weight is on the suspension.
Replace the sway bar and brake line if necessary. Then refit the wheel and torque tighten this, again to vehicle manufacturers specifications.
Lower the vehicle and settle it back on its suspension. Torque the strut tower and top mount bolts and replace the plastic cover.
Finally check and adjust wheel alignment as necessary and perform a small road test to ensure the steering wheel is straight.
Delphi Technologies are taking bookings for training courses taking place in 2020 and 2021 at its Warwick training centre, which are open to all. Click here to find out more or email firstname.lastname@example.org.