It’s the preverbal question about the chicken or the egg–which goes bad first and did it take-out the other?
When you have noticeable vibration shifting your car into drive or reverse but are not yet moving or vibration at high-load levels, like drive-off and gear shift, you probably have a bad mount. Often you will hear an audible “clunk” when you put your car in gear or vibration that smooths out as you start driving.
Jumping to the end of the story – always replace engine mounts as a set and it usually makes sense to do the transmission mount at the same time for latitudinal-mounted drivetrains.
This is particularly when the car has a single transmission mount—like most Mercedes and BMWs. The bulk of the labor and parts expense is in the engine mounts; it often makes sense to do them at once:
• we’re already there
• you’ll experience the full benefit of new mounts
• bad engine mounts put strain on the transmission mount; its failure
is not far behind. The opposite is also true.
Engine mounts hold your engine in place. They absorb the shocks of the road and the vibration of the connected engine and transmission and keep them in place. A defective transmission mount has the same impact on driving comfort as a defective engine mount.
Most engine mounts are fluid-filled. You will often see them leaking or drip and stains on the aluminum base of the mount or frame. Most transmission mounts are solid rubber and deteriorate and crack with use and age.
When a mount breaks the engine and transmission are less secure, subject to a higher amount of vibration and often cause the failure of the other mounts. Oil and transmission fluid leaks can also accelerate the deterioration of mounts.