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Pelican Technical Article:

BMW E30 3 Series Transmission Mount Replacement
Jared Fenton
Wayne R. Dempsey

Difficulty Level: 3
Difficulty scale: Adding air to your tires is level one
Rebuilding a BMW Motor is level ten

     Are you feeling a weird vibration from your car when you shift or accelerate? Is the shifter rocking back and forth like it’s possessed? Are you hearing and feeling a huge knocking noise when you drive? All these are a symptom of old or broken transmission mounts. In this tech article I will go over the steps involved with replacing the transmission mounts on the BMW E30 3 Series from 1984-91. Keep in mind that this article is specific to my 325is, however this article does apply to four-cylinder models as well. A lot of people have been asking me to do an article on this subject, so here goes.

     Transmission mounts have two primary functions in a car. One, they secure the transmission to the vehicle’s chassis, and prevent the transmission from crashing into the underside of the car when you accelerate. When you hit the gas, the torsional forces of the mainshaft turning causes the transmission to twist as it delivers power to the rear wheels. The transmission mounts prevent this. Unfortunately, bolting the transmission direct to the chassis also results in transmitting the vibration from the engine and transmission all throughout the car. The solution is to mount the transmission to the chassis using rubber mounts. The rubber acts as a damper, allowing the transmission a certain amount of play, and keeps it from rattling you to death as you drive.

     The first step in fixing the problem is to jack up the car as much as possible so that we can access the tranny mounts. I recommend that you place the car as lever as possible on four jack stands as this will help you greatly. If you are not familiar with jacking up you car, I highly recommend you read Wayne’s article on jacking up your BMW. Here is a link to the article.

     With the car firmly secured on jack stands, climb under the car and look at the rear of the transmission, right where the driveshaft meets up with the tranny. On either side, you will see two small rubber mounts securing the tranny to the chassis. This is what we will be replacing.

     We first need to loosen the nuts that hold the mounts in place. There are two nuts on the top of the mount and two on the bottom. Loosen all of these then remove them. Now place a jack directly below the transmission casing and place a piece of wood in between the jack and the tranny. This will help distribute the weight of the tranny.

     Now start jacking up the tranny very slowly. We want to jack it up just enough so we can remove the mounts. USE EXTREME CAUTION when removing the mounts as the tranny will be only supported by the jack. You can lose fingers here if you are not careful. Once you have jacked the tranny high enough, remove the old mounts.

     Now take the new mounts and first place them into the crossmember attached to the chassis. Line up the studs out of the top of the mounts with the mounting holes on the transmission casing and slowly lower the jack until the new mounts are supporting the weight of the transmission. Keep in mind that it may take a few tries to get these lined up correctly.

     Once the new mounts are bearing the load, thread new self-locking nuts onto the top and bottom studs. It’s important to use new self-locking nuts as they are designed to only be tightened once. If you re-use them, they can come loose and possibly cause a huge disaster.  Once all the nuts are threaded on, torque them to 30 ft./lbs.  Now jack the car up again to remove the jack stands from all four corners of the car, and lower it back down to the ground.

     Well, there you have it - it's really not too difficult at all.  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.

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