BMW E30 3 Series Motor Mount Replacement
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 motor mounts. In this tech article I will go over the steps involved with replacing the motor 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.
Motor mounts have two primary functions in a car. One, they secure the motor to the vehicles chassis, and prevent the motor from crashing into the fenders. When you hit the gas, the torsional forces of the crankshaft turning causes the motor to twist as it delivers power to the rear wheels. The motor mounts prevent this. Unfortunately, bolting the motor direct to the chassis also results in transmitting the vibration from the engine all throughout the car. The solution is to mount the engine to the chassis using rubber mounts. The rubber acts as a damper, allowing the engine a certain amount of play, and keeps it from rattling you to death as you drive.
Over time, the rubber mounts begin to wear out due to constant vibration, the torque of the engine twisting the mounts, and general road grime and oil. Eventually the rubber will rip or fail, causing the motor to twist excessively. The fix for this is to replace the mounts.
The first step in replacing the mounts is to first determine the location. Open the hood and look down on either side of the engine. You will see a rigid metal link that bolts to the engine block on either side. At the end of these links is a rubber spacer. The spacer is the motor mount.
It's a good idea to disconnect the battery at this time as well. We will be working around the general area of the starter motor, and it is possible to accidentally touch the terminals with a wrench. I have seen wrenches welded to starter motors because someone forgot to disconnect the battery.
Now chock the rear wheels and jack up the front of the car. Be sure to secure the front end on good quality jack stands. NEVER rely on a jack to hold the car up. You are asking for trouble. For those of you not familiar with how to jack up the front of your car, I highly recommend you check out Wayne's article on jacking up your BMW. It applies to the E36 3 Series, however it will provide you with a clear understanding of how to jack up your BMW correctly. Here is a link for the article.
Once the front end is up on jack stands and is firmly supported, we can move onto the next step. Look under the car for the nut that secures the motor mount to the chassis. Remove each nut from either side. Don't worry about the motor falling or shifting at this point, as the weight of the block will keep it supported in place. Now, we will want to remove the upper nut on each of the mounts. You may find it easier to access these from inside the engine compartment.
Now comes the tricky part. We will want to actually jack up the engine enough so that we can pull the old mounts out. The best location to jack the engine is from the oil pan. Get a piece of wood about a foot long by 6 inches and place it in between the jack and the oil pan. The wood will help distribute the weight of the engine and help prevent you from damaging the oil pan.
Now start jacking the engine up. Go very slowly and look for any hoses, lines or wires that may be stretching. If you see any of this, STOP, and address whatever may be stretching. Now keep jacking just until you have enough clearance to pull the old motor mounts from between the engine and the chassis. BE EXTREMELY CAREFUL when doing this, as the engine will only be supported by the jack. In some cases it may be helpful to put jack stands under the wood while the engine is up. This will provide extra safety.
Once the old mounts are out, slide the new mounts into position on the chassis. Now slowly lower the engine until the threads on each mount slide into their respective holes on the engine link. It may take some time to get these lined up exactly. Once lined up, lower the engine completely so that the new mounts are bearing the load from the weight of the engine.
Now remove the jack from under the car and thread new self-locking nuts onto both sides of each mount. It's important to always use new nuts as they are designed to only be tightened once. If you re-use the old nuts, they can slowly work themselves loose and possibly cause a huge disaster. Once all the nuts are threaded on, torque them to 30ft./lbs.Now jack the sides of the car up and remove the jack stands. Lower the car 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.