BMW M3 Brake Ducting

After a few years of living with overheating brakes on my 1995 M3, I decided to do something about it. Here you will find several photos illustrating my solution to this problem. Materials consist mainly of aluminum sheet, tube and grill, adapted from their intended use as rain gutters. Total cost including about $50 for the high temperature brake hose came to under $90.

To the undiscerning eye, there is no outward appearance of any changes.

Click here for Front Views of the Completed Duct

To build the duct, I removed the fog lights, and built a tapered aluminum box that fits in behind the fog light opening, the existing brake duct opening, and extends right to the middle of the lower front grill. This increases the duct opening from 76 square cm. to 470 square cm., or a bit more than 6 times. A flexible 2.5 inch diameter tube exits the rear of the box and is routed to the inner hub of each wheel, forcing air into the inside of the rotor.

This seems to work very well, as I haven't had any brake fade, let alone warped rortors, since I have installed the duct.

The process I used to fabricate these ducts is as follows:

• remove the front wheels and inner front fender liners
• remove the lower left and right plastic trays in front of each wheel well
• disconnect the fog lights
• remove the fog lights and brackets
• remove the left and right black plastic bumper trim from the bumper, exposing the bumper mounting bolts
• remove the front bumper
• using cardboard and tape, build a template of the scoop (photo). You may have to build several models to get it right.
• I used a section of aluminum 'rain diverter' from a building supply store to make the ducts themselves, although any aluminum sheet will do. The advantage of the rain diverter is that it already has a 90 degree bend in it, which served my purposes. The sections of aluminum can be screwed together with small sheet metal screws, and then taped with aluminum duct tape. (photo)
• I used a rain gutter tube, removed from a downspout, as the outlet port for the duct, and atttached 2.5" flex brake duct to this with a hose clamp. If you slice the spout along its length with metal cutters, you can slip the brake tubing into the duct, then clamp it on the outside.
• route the flex tubing around to the indside of the wheel well, and attach to the lower suspension mounts. I encased the tube with aluminum downspouts to minimize abrasion where the nylon ties attach it to the frame. (photo1) (photo 2)
• cut out a 2.5" x 2" hole in the inner face of the existing brake dust shield, and screw into this another downspout. I installed a downspout on the inside of the dust shield, trimmed such that it forced air only into the inside of the rotor. (photo)
• secure the scoops in place with angle brackets mounted on the upper edge of the bumper.
• install an expanded aluminum mesh (painted to match your car), made from a rain gutter leaf shield, across the front of the entire grill area. Screw this in place with stainless #8 screws in the old fog light holes.(photo)
• a photo of all part used can be found here (photo)

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