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Pelican Technical Article:

BMW E30 3 Series Cross-Drilled Front Brake Rotor Upgrade
Jared Fenton

Difficulty Level: 2
Difficulty scale: Adding air to your tires is level one
Rebuilding a BMW Motor is level ten

     This article is the one in a series that will be released in conjunction with Wayne's upcoming book, 101 Projects for Your BMW 3-Series.  The book will be 256 pages of full color projects detailing everything from performance mods to timing the camshafts.   With more than 350+ full-color glossy photos accompanying extensive step-by-step procedures, this book should be a staple in any 3-Series owner's collection.  See The Official Book Website for more details.  The book is due out in October 2005.   

     In this technical article we will focus on upgrading the braking system on the BMW E30 3 Series from 1984-92. This technical article is specific to my 325is, however the procedures contained herein apply to all E30 3 Series models. 

  No matter how fast you go, it is always crucial to have the brakes to slow you down. In this instance we will focus on installing cross-drilled front rotors on your car. Why upgrade to cross-drilled rotors? Basically for improved brake cooling. When on a racetrack, brake disc temperatures can reach temperatures of over 1000 degrees Fahrenheit. If you have ever watched NASCAR or Formula One, you may have noticed the brake discs glowing through the wheels of the car. This shows just how hot these brakes can get. When brakes get this hot, it can cause what is commonly known as “brake fade”. What this means is that the brake fluid inside the caliper gets so hot it begins to boil. When the brake fluid boils, it causes bubbles of air to form inside the calipers, causing the clamping strength of the calipers to literally fade. You may have noticed signs on mountain roads saying, “steep grade, use lower gears”. What this actually means is, “Don’t ride your brakes going down a hill” When you go down a steep grade that may last several miles, your brakes will heat up, causing brake fade.

  Installing cross-drilled rotors is one way to keep brake temperature down. By drilling holes through the face of the rotor, air is allowed to circulate through the disc as it spins. This circulation helps to reduce heat from the brake discs. You may have noticed that in the center of the stock brake discs there are several vanes radiating from the center of the disc outward. This is what is called a ventilated rotor. As the brakes disc spins, the vanes act like a giant fan, drawing air inward to cool the brakes. Typically this is an effective means of cooling. Cross-drilled rotors take it one step further.

  So let’s begin. The first step of installing the rotors is to secure the rear wheels of the car with wheel chocks or other means to keep the front rolling once you have the front end of the car up in the air. The next step is to loosen the lug bolts on the front wheels with the car still on the ground. It’s important that you merely loosen the bolts and not remove them. Next, Place a floor jack under a reinforced portion of the car and place a block of wood in between the jack and the chassis. This will help evenly distribute the weight of the car. Now, jack the side of the car up and place a jack stand under the side of the car at a reinforced portion of the chassis. Repeat this procedure for the other side of the car. Also, NEVER rely on the floor jack to support the weight of the car. ALWAYS use quality jack stands to hold the car up. You don’t want a 3000lb.+ car falling on you when you are underneath. For those of you not familiar with how to properly jack the car up, I highly recommend you check out Wayne’s article on jacking up your BMW.


  With the car now up in the air and firmly supported on jack stands, remove the lug bolts on both front wheels and remove the front wheels. You will now see the brake assemblies. To remove the old rotors, we will first need to loosen the brake disc-retaining bolt. This is the small Allen head bolt on the rotor face. These can be a handful to remove. What I recommend is to spray the bolt with a good amount of WD-40 or any other penetrant spray and let it sit for a few hours. This will allow the penetrant to work through the threads and make it much easier for you to remove. These bolts have a tendency to rust to the rotor face. It may even be helpful to carefully heat up the bolt with a torch. CAUTION: be sure to take extreme safety precautions anytime you are working with a torch. This means wearing the correct clothing, safety goggles, and making sure there is no flammable material in the immediate area. Next, have a helper apply the brakes. This will secure the brake rotor and allow you to loosen (but do not remove) the bolt.

  We will now need to remove the brake calipers. Begin by first unplugging the brake wear indicator sensor on the driver’s side. This is the small sensor coming out of the caliper in between the brake pads. Now look at the top of the caliper. You will see two bolts that secure the upper caliper to its frame. We will need to remove these bolts. Use an open-end wrench to secure the two locknuts on the inboard of the bolts and loosen the securing bolts. Once removed, you will be able to remove the upper caliper from its frame. Be careful not to damage or twist the rubber brake line that feeds into the caliper. Use some zip-ties or ropes, and secure the caliper out of the way by tying it to the chassis. You should be able to simply pull the old brake pads out of the caliper, or if they are still on the frame simply take them off and throw them away, as we will be installing new brake pads.

  Now we need to remove the lower caliper frame. This is held to the hub assembly by two large bolts on the backside of the hub. These bolts are torqued on very tight, so you may need a breaker bar to get them loose. Once loose, remove the bolts and pull the frame off the hub. Repeat this for both sides.

  We are now ready to remove the old rotors. Remove the already loosened retaining bolts and pull the rotors off. You may find that the old rotors are stuck to the hub. Use a rubber faced mallet against the rotor face to free it up. Once free, remove the rotors from both sides. Now is a good time to get a can of brake cleaner and clean off any crud that may have built up on the backside of the dust shields.

  Now take the new cross-drilled rotors and line them up on the hub faces, as the old rotors were oriented. It’s recommended that you always use new retaining bolts to hold the rotors on. Put a small dab of anti-seize compound on the threads of the bolts then thread them into the hubs, securing the rotors. Anti-seize compound helps to keep the bolts from seizing to the rotors/hubs, and will make it much easier to remove them in the future. Tighten the new bolts down snug but do not torque them at this time.

  Take the lower caliper frames and place them back onto the hubs, and thread in the securing bolts. BMW recommends you torque these bolts to   ft/lbs. Be sure to clean off the frames with brake cleaner and clean off the threads on the bolts. It’s also a good idea to put dabs of anti-seize compounds on the threads as well.

  Now look at the new brake pads, and install the brake pad wear indicator from the old pad onto the new pad. If the sensor has worn down to the point where the metal contacts inside are exposed, replace it with a new one. Now take the new pads and place them on the lower caliper frame.

  It is now necessary to compress the upper caliper pistons. As the old brake pads wear, the caliper piston expands further out of the caliper housing. It is necessary to compress it back into the caliper to allow the new pads to fit into the caliper. Take a large C-clamp or brake piston compressor and slowly work it back inside the caliper. Once the piston is compressed, Slide the upper caliper over the brake pads in the lower frame and press down. This will put tension on the springs located at the tops of the brake pads, holding them in place. Be sure to also route the wires fro the brake pad senor through the caliper.

  Now line up the mounting bolts for the upper caliper and thread them in by hand to secure the caliper. Use an open end wrench to secure the locknuts and torque the mounting bolts to    ft./lbs. Take the electrical connection for the brake wear sensor and plug it back in. Now have a helper apply the brakes, and torque the brake disc retaining bolts to    ft./lbs. 

  Put the wheels back on the car and snug up the lug bolts so that the wheels sit flush against the hubs. Carefully lower the car and tighten the lug bolts with the car on the ground.

  And that’s it, you’re done!

     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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