2008 BMW 650i Trans Mount Replacement Cost

Depending on the orientation of the engine compared the the vehicle, a transmission mount will either be located near one of the front wheels, between the transmission and front floorboard, or underneath the vehicle somewhere between where the front seats would be. These mounts provide not only a mounting point for the transmission, but they provide a barrier to vibration from the engine and transmission. This vibration damper allows the vehicle to stay quiet and feel smooth, especially when the transmission is being shifted to driver or reverse and under heavy acceleration. Transmission mounts will typically have a metal casing which surrounds a tough rubberized material, which surrounds another metal component. Let's examine the functionality of this form.

The transmission mounts outer casing provides a strong mounting point to the vehicle. This is made of metal because it will support the entire weight of the transmission, allow bolts to be tightened into it, and must be machined perfectly flat to avoid vibrations. Inside this metal housing, the rubberized damper is tightly fit to the outer casing and molded around the other metal portion which will be described momentarily. This prevents metal contact from the transmission side of the mount to the chassis side of the mount. Sometimes, for additional vibration prevention, the rubberized portion is filled with liquid as well. The metallic piece in the center of the rubberized insert is rigid and strong, and provides a way for the transmission to attach to the rubberized portion, which, again, is locked into the outer housing. When the transmission side metal bracket is bolted to the transmission and the chassis side is bolted to the chassis, the transmission is actually supported by the rubberized insert, and linked to it by the metal bracket and housing discussed.

Since vibration prevention is the reason for the design of the transmission mount, you can guess that excessive vibration from the drivetrain is likely due to engine or transmission mount failure. Also, when the transmission mount is completely worn out, meaning the rubber insert has worn and failed, the transmission may begin to make clunking noises against the chassis. This is the noise of the metal bracket and housing contacting very harshly with very little padding. This would be noticed the most when the vehicle is being shifted into reverse or drive, when braking quick and hard, or when accelerating rapidly. In some cases, the transmissions movement may even cause the check engine light to illuminate or the engine to stall. This is due to excessive movement of the engine and transmission, which allows components to be damaged or loosened. Lastly, front wheel drive vehicles may have clicking upon turns due to the sagging transmission mount causing the CV axle to bind while turning and accelerating.