The car starts shaking oddly at idle, you feel a vibration through the wheel and seat at a red light, and when you shift into gear there's a dull thud from the front. Most drivers think clutch, spark plugs or suspension first. In a fair number of cases, the culprit is a completely different part that nobody mentions until they get to a mechanic: the engine and gearbox mounts. This guide explains how to spot them, why this fault is so often misdiagnosed, and what to ask for at the workshop.
What engine and gearbox mounts do and why they fail
In every car, the engine and gearbox aren't rigidly welded to the body. They sit on mounts, usually three or four pieces, arranged so the engine sits stable and vibrations don't transfer directly into the cabin. The engine mount holds the engine itself (usually two pieces, on the left and right), and the gearbox mount holds the gearbox housing (usually one, on the opposite side from the engine). The third or fourth is the lower so-called torque mount that stops the engine from rolling under sudden acceleration.
Mounts are a combination of metal and rubber. The rubber is what damps vibrations, and it slowly ages, dries out and cracks under heat and engine vibration. On newer cars a lot of manufacturers use hydraulic mounts (with fluid for vibration damping inside the mount itself). They damp better, but when they fail they can also leak, so you often see fluid around the engine or gearbox.
The main reasons for failure: rubber ageing, aggressive driving with hard acceleration and braking, bad roads, and oil leaks from the engine that eat the rubber from above. On average, in BiH conditions mounts last between 100,000 and 200,000 kilometres, depending on driving style and the type of mount. Hydraulic ones can go earlier.
The main failure symptoms you'll feel from the driver's seat
When a mount gives up, the engine no longer has a firm support and starts moving more than it should. The driver feels every bit of that movement as a vibration or a thud. The most typical symptoms are:
- Stronger vibrations at idle. The car is sitting at a light, the engine is running, and the wheel and seat shake noticeably. If you put it in neutral and press the brake, the vibration often stays.
- A dull thud when shifting into gear. On automatics, going from P to D or from D to R is followed by a noticeable thud that wasn't there before. On manuals, you feel something similar when releasing the clutch.
- A jolt under sudden throttle. When you press the pedal harder, the engine visibly shifts, and you feel that as a brief jolt through the whole car. The same thing happens when you suddenly let off the throttle.
- A metal-on-metal sound over bumps. Going over a speed bump or a pothole sometimes makes a dull thud that comes from the engine bay, not the suspension.
- A visibly tilted engine. When you open the bonnet and look at the engine from the side, you can see it leaning to one side more than it should.
On some models, as soon as you open the bonnet you can see the broken-up rubber on the mount with the naked eye, or fluid leaked from a hydraulic mount that looks like a dark patch around the part itself.
Why this fault often gets blamed on the clutch, spark plugs or suspension
The problem is that the symptoms of a failed mount overlap really well with other, much better-known faults. Idle vibration is a classic description of a bad spark plug, a faulty coil pack or a dirty throttle body. A jolt under throttle sounds like a slipping clutch or a problem with the automatic gearbox. Thuds over bumps first send the mechanic toward suspension, control arms and tie rods.
A driver will come into the shop with the story "it shakes when it stands" and leave with new spark plugs, with the vibration still there. Then the coil gets swapped. Then the lambda sensor. Then it's off to the gearbox. Only when somebody opens the bonnet and actually looks at the mounts does the cause show up. This isn't a rare scenario, it happens regularly, and that's exactly why we always look at the mounts first when somebody reports vibrations and thuds that don't fit the typical engine-fault picture.
Another problem that comes with broken mounts: when the engine moves too much, it loads up the exhaust system. The exhaust starts cracking at the joints faster than usual. Pipes and hoses around the engine get pulled and split. So one neglected mount can kick off a chain of faults.
How mounts are checked at the workshop
The check isn't complicated, but it needs an eye and the car on a pit or a lift. At our shop we start with a visual inspection. We look at the rubber on every mount, looking for cracks, crumbling and signs of fluid. A hydraulic mount that has leaked is obvious straight away, with a greasy patch around it.
The second step is a load test. The car is standing, the engine is running, and the mechanic stands to the side and watches how much the engine moves when somebody presses the brake and snaps the throttle in D, then in R. A healthy mount holds the engine steady, a tired mount lets the engine visibly jerk. On automatics there's another simple test: shifting from P to D, then to R, with your foot on the brake. If every shift comes with a dull thud, the gearbox mount or the torque mount are the first suspects.
What we always recommend: if one mount is found to have failed, all the others should be checked too. The reason is simple, because when one gives up, the engine's weight gets pushed onto the rest, they work double, and they usually go within a few months. It's much more cost-effective to replace two at the same time than to come in twice for the same job.
When to replace and what to expect from the repair
A broken mount isn't an emergency in the sense that the car can't be driven, but it's also not something you can put off for a year. The longer you drive with a broken mount, the more load goes on the other mounts, the exhaust, hoses and the gearbox housing itself. In extreme cases the engine can fully tear off the mount and rest on the lower block or the exhaust, which immediately causes more damage.
The parts themselves usually aren't expensive, especially classic rubber mounts. Hydraulic ones are a bit pricier because they're more complex. What varies is the labour around fitting. On some engines a mount gets swapped in half an hour, on others the whole engine has to be lifted because the mount is hidden behind other assemblies. That's why labour cost differs from car to car.
That's why we always do an estimate before the job. We look at which model it is, which mount is in question, whether it makes sense to replace the others as well, and then we quote the price. The price depends on the condition of the car and the workshop, so get in touch for an estimate or book an appointment and we'll look at the mounts on the spot.
If your car shakes at idle, thuds when you shift into gear or jolts when you give it throttle, don't go straight to new spark plugs and a clutch. Open the bonnet, look at the mounts, or drop by and have somebody do it for you. Often the fix is much simpler and cheaper than it seems at first glance.