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One of the most common parts to deteriorate on the BMW is the engine and transmission mounts. The rubber that is contained within the mounts becomes old and brittle, and doesn't perform a good job of isolating the drivetrain from the rest of the chassis. Old, worn out motor and transmission mounts can cause shifting problems because the drivetrain is no longer firmly held in its position. One sign of this failure mode is the gearshift knob jerking backwards under hard acceleration or difficulty selecting gears during cornering. A visible sign that the motor mounts need replacing is the appearance of cracks in the rubber of the mounts. The rubber will deteriorate over the years and need to be replaced, even if the car has relatively few miles on it.
The transmission mounts are easier to replace than the engine mounts, and are very similar on both the E30 and E36 BMWs. A transmission mount bar is bolted to the rear of the car and supports the transmission. Begin by jacking up your car and placing it on jack stands. Now, place a jack under the transmission to support the weight. Then, carefully remove the transmission mount bar from the car (Figure 1 and Figure 2). You may have to bend the heat shield slightly out of the way to access the bolts that mount the transmission bar to the chassis. Close-up views of the old transmission mounts are shown in (Figure 3, Figure 4 and Figure 5).
Remove the old mount by removing the nut on the underside of the mount bar (Figure 6). New mounts are shown in (Figure 7), and are simply bolted in place of the old ones. There is a boss on the bottom of the mount that needs to line up with a notch on the transmission mount bar. This boss/notch combination prevents the transmission mount from rotating.
Stock BMW transmission mounts are not known for their performance or reliability. The purpose of the transmission mount is to isolate the chassis of the car from vibration that the transmission will transmit during normal driving. The transmission is connected to the engine, and has a tendency to twist and turn as the car accelerates or decelerates under heavy braking. If the transmission mounts are flexible and sloppy, then there may be a misalignment of the transmission with respect to the chassis of the car. This may cause what is commonly known as a miss-shift or in laymen's terms a "moneyshift." A mis-shift will sometimes cause the driver to accidentally shift from a high gear to a much lower gear and over-rev the engine. An over-rev is very damaging to the engine and typically results in the valves hitting the tops of the pistons and bending.
One solution is to use the early style BMW 320i transmission mounts. They are thicker, they have a tendency to flex less than the stock ones, and for the most part they are a bolt-in application. Another solution is to use better designed transmission mounts and brackets. I recommend the ones produced by UUC Motorwerks. The standard mount is shown beside the UUC mount in Figure 8. These new and improved mounts isolate vibration, but perform a better job at keeping the transmission correctly aligned with the chassis. In addition to the UUC transmission mounts, I also recommend the UUC Tranny Mount Enforcers (TMEs, shown in Figure 9).The TMEs hug and constrain the transmission mount and reduce the deflection of the amount under vigorous driving. The addition of the UUC mounts and the TMEs are probably the best insurance you can provide to prevent expensive mis-shifts.
The upgraded UUC transmission mounts are available in black or red.The black versions are tailored to street driving - the red ones are designed for track or autocross use. (Figure 10 and Figure 11) shows the red UUC transmission mounts installed on the transmission mount bar. Grease up the inside of the TME prior to installation, to minimize chaffing of the mount (Figure 12). The TMEs are installed on the top of the transmission mounts, beneath the transmission mounting flange (Figure 13 and Figure 14). The flange from the transmission mount should fully protrude through the TME as is shown in (Figure 15).
The completed mount assembly is shown attached to the transmission in (Figure 16 and Figure 17). The transmission shown in these photos was out of the car for a clutch job. When installing the mounts back into the car, tighten up the bracket to chassis bolts first. Then lower the transmission onto the bushings and tighten the top nuts, securing the transmission to the bar.
When you are finished, you should feel an improvement in the shifting of your car, and the drivetrain vibration should feel a little tighter and less sloppy. If you would like to see more technical articles like this one, please continue to support Pelican Parts with all your parts needs. If you like what you see here, then please visit our online BMW catalog and help support the collection and creating of new and informative technical articles like this one. Your continued support directly affects the expansion and existence of this site and technical articles like this one. As always, if you have any questions or comments about this helpful article, please drop us a line.