This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your BMW 3 Series. The book contains 272 pages of full color projects detailing everything from performance mods to timing the camshafts. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any 3 Series owner's collection. The book was released in August 2006, and is available for ordering now. See The Official Book Website for more details.
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The BMW 3-Series cars have a hydraulic clutch engagement system - there are no cables involved with the actuation of the clutch. Although this actually creates a more reliable clutch system over time, there can be a failure or break-down of the system if the slave or master cylinder get old and begin to leak or fail. A spongy feel to the clutch pedal, grinding of gears when shifting, long pedal travel, and hydraulic leaks under the car are all signs that one or more components of the system have failed. The first place I like to start is the clutch slave cylinder, as it is easy and inexpensive to replace. Replacement of the slave cylinder is a snap. Its location is easy to get to from underneath the car. The slave cylinder is located on the left side of the transmission (Figure 1). Two nuts fasten it to the transmission. First, disconnect the hydraulic line from the cylinder. Make sure you use a flare-nut wrench to remove the hose. These hydraulic fittings have a tendency to strip if you don't use the proper tool. Also, inspect the clutch slave line - you might want to replace it if it's bulging, or shows signs of cracking in the rubber. Before you disconnect the line, make sure that you have a drip pan to catch the fluid that will leak out.
Now, remove the two nuts that hold the cylinder to the transmission. The slave cylinder should remove easily. Install the new one and reattach the clutch fluid line.
The system now needs to be bled. I like to use the Motive Products Power Bleeder for this task (Figure 2). For more information on using the Power Bleeder, see the Pelican Technical Article on Bleeding BMW Brakes. Attach the power bleeder to the top of the master cylinder reservoir (Figure 3) and pump up the pressure in the bleeder. Move to underneath the car and attach your bleeder hose to the bleed nipple on the slave cylinder (Figure 4). Let the system bleed out until no more bubbles appear.
When finished, remove the bleeder system, lower the car, and try the clutch again. The pedal should have a good feel to it, and the clutch should engage normally. If you are still having problems, you should try replacing your clutch master cylinder next (tech article coming soon).
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