Reader Question: I have a 1993 Saturn 4 door sedan with a manual transmission, and recently had to have the motor mounts replaced. My question is, what causes motor mounts to have to be replaced? Do they just wear out? Does hard driving cause them to go bad?
Thank you, Kathy
Thanks for your e-mail. A motor mount is made up of a piece of rubber sandwiched together by two plates of metal. Click for picture. These "rubber sandwiches" bolt the motor and transmission to the frame of the car. The vibration caused by the engine is absorbed by the rubber. It would be an extremely rough ride without these rubber cushions. The engine and transmission are constantly moving and flexing from the torque...when you give the engine gas you cause the motor and transmission to move or flex...and this movement is restricted by the motor mounts, otherwise the engine could pop out of the hood or fall on the ground. Most cars have three to six motor and transmission mounts depending on the model and year of the vehicle.
What causes the motor mounts to go bad? Rubber stretches and loosens with age and use. When the motor mounts start to loosen, they allow the motor and transmission to flex and move more than they should in the small confines of the engine compartment. When the engine moves, it also pulls on wires, hoses and other items that really should stay stationary. Excess movement of one mount will cause the other mounts to stretch more than they can withstand, thus breaking them. An oil leak that is allowing oil to collect on the rubber part of the mount will deteriorate the rubber as well. Click for picture.
How do you know you need to replace the motor mounts? The only clue you may have as a driver is a rough vibration, especially at idle. You usually can't feel the vibration caused by a bad motor mount while you are driving the car. Switching between drive and reverse may cause a change in the vibration felt as the torque changes direction. If you notice a change in the vibration of the engine as you switch gears, the vibration is more than likely a bad motor mount as opposed to an engine miss or the need for a tune-up. If the rubber is cracked in two, you may also hear an occasional thump as the loosened motor bangs against the body of the car.
When do you replace the motor mounts? If you notice a strong vibration at idle, get the motor mounts checked right away. Neglecting this repair can cause other damage as the too-mobile engine or transmission puts undue stress on belts, hoses, and other connected parts. The motor mounts on most cars are not easily visible, and it's even harder to tell if they are worn or broken by sight, so it's not an item that you can inspect as part of your regular maintenance schedule. Your mechanic probably won't check your motor mounts unless you indicate a possible problem, or unless he notices symptoms of a bad motor mount during a test drive.
At ten years old, it is certainly reasonable for your car to have a bad motor mount. This repair does tend to be expensive because it is such a labor-intensive job. The mechanic will have to take several parts off of the car to get to the motor mount, and some motor mounts are expensive parts depending on the make and model of the car.
This valuable tidbit is just one of the many cost-saving items you will learn about when you visit our Website TrustMyMechanic.com. I hope this helps.
Austin C Davis
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