You’ve got bad strut top mounts; you need to drive the car, should you, and how long for? I’m sorry to say it’s not as easy as saying x amount of miles. But assuming they are not hanging on for dear life, you may be able to get 1000 miles or a month of driving with bad strut mounts; I’ve explained more on this below.
What does a strut top mount do?
Strut mounts or top mounts, as they are also known, attach the suspension strut leg to the vehicle. Located at the top of the shock absorber, they usually consist of a rubber plate with studs(to connect to the car chassis leg) and a bearing that sits between the spring pan and strut mount. They have more than one job, which includes:
- Support – The top mount supports the upper end of the shock absorber by holding the coil spring in place. It also secures the shock absorber strut and the rest of the suspension to the chassis.
- Damping – The strut mount helps absorb and dampen the vibrations from driving over bumps and potholes. Although the coil springs and shocks do most of this work, the rubber strut mount stops any vibrations from being transferred through the car metalwork into the cabin.
- Noise reduction – The top mount helps isolate noise generated by the suspension system and the road. It does this by absorbing the vibrations created from driving.
- Allow for movement – Inside the strut mount is a bearing, but not like a wheel bearing; it is usually just a plastic ring. Turning the steering wheel allows the shock absorber to turn with the wheels while still attached to the car. Without a top mount or its bearing, the shock absorber would be bolted directly to the chassis, and the wheels wouldn’t turn.
How long can you drive with a worn strut mount?
Driving with a worn strut mount differs from driving with a snapped coil spring. You aren’t necessarily in any immediate danger. Strut top mounts don’t tend to fail catastrophically to a point where you cannot drive the car. Generally, there tends to be an excessive play that gradually gets worn over time, so it’s not uncommon to have seen drivers doing 5000+ miles on a worn strut mount.
However, the problem with prolonged driving is the extra stress and wear it causes to other related components. For this reason, you should only consider driving for about a month or 1000 miles once you know you have a problematic strut mount and seek urgent repair.
Even with that, driving is done at your own risk. Once a strut mount gets bad, it can cause the car to develop some driving characteristics which aren’t safe to continue with. Eventually, they will get so bad that physically you won’t be able to drive the car.
What happens if you drive with a bad strut mount?
If you continue driving and ignore the signs, you have bad strut mounts, and driving could become problematic and costly to repair.
When the strut mount fails, the bearing collapses and wears away at the rubber mounting. This puts unnecessary pressure on shock absorbers, suspension bushes, tires, and the transmission, which can cause each of them to fail, and that’s when just driving along in a straight line. When turning the vehicle, the car may snatch to one side or become unsteady mid-corners, which is not ideal or safe; you don’t want the car to be forced into hitting the curb more than once.
How long should strut mounts last?
The Strut mounts typically last the same length as the struts, approximately 50,000 – 80,000 miles or 5 – 8 years.
Whenever the struts are removed to replace a broken coil spring or a worn shock absorber, you should always simultaneously change the strut top mounts.
Symptoms of bad strut mounts
The most commonly found symptoms of bad strut mounts are:
- Uneven tire wear
- Tire rubbing when turning
- Knocking noises when turning, especially at low speeds
- Clunking noises when going over bumps
- Steering wheel off center
- Noises when braking heavily
- Car swaying when corning (feels like driving a boat through corners)
It’s crucial to remember worn shock absorbers and even broken coil springs share some of the same symptoms. Driving with either broken or worn can be more severe than driving with a bad top mount. It would be best if you didn’t assume and properly checked to find the correct cause of the issue.
How do you check bad strut mounts?
You look for excess movement or knocking noises when checking for bad strut mounts. The strut mount bearing wears down, as does the rubber with age and constant use. Checking is straightforward and similar to checking for a bad shock absorber strut. The strut mount can be checked while they are still on the vehicle in two ways.
One is with the vehicle on the ground and the hood open. Put one hand over the top of the strut mount and the other on the cross member, press down on the car, and bounce it. You may hear or feel a knocking from the top mount if they’re worn.
The other is to jack the car up and use axle stands to secure the vehicle safely. If you put a leaver bar under the wheel or hug the wheel and try to force the wheel upwards, what happens in the spring and shock absorber should compress; however, if the top mount has failed, before they both compress, there will be some play (movement), and you may hear knocking. Vehicle dependant, you can also look at the strut mount from the engine bay and visibly see this excess movement.
Changing strut mounts
Changing strut mounts should only be done by a trained professional with the correct tools. The springs must be removed from the shock absorber to replace a top mount. Coil springs are kept under high tension and cannot be removed with a spring compression tool.
If you have a friendly local mechanic with a spring compressor, if you take the suspension leg off the car, they might swap the new top mount out for you, and you can then refit the strut leg yourself. The only other thing you should do is recheck the wheel alignment after replacing the top mounts; this will not be correct afterward.
Although, as we’ve touched on in this article, you can drive with worn strut mounts and maybe even for an extended period (at your own risk). You should be aware that they can get really bad, and you won’t be able to drive when they collapse.
One last point I want to reraise is replacing worn strut mounts are straightforward forward; however, it must only be done with the use of a coil spring compressor, do not attempt to remove the top mount from the shock absorber with the spring under tension; you will seriously injure yourself or someone around you! For this reason, I strongly recommend that this is one of the few repair jobs best left to a good mechanic.