BMW Convertible Rear Window Replacement Wayne R. Dempsey
Difficulty Level: 6 Difficulty scale: Adding air to your tires is level one Rebuilding a BMW Motor is level ten
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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One of the most common complaints of convertible owners is the condition of the rear window. It’s manufactured out of a clear plastic, and as such, it does not have the longevity of a clear glass window. With time and exposure to the elements, the window can become scratched, damaged, or faded.
The good news is the rear window is zipped into place and is relatively easy to replace. I say “relatively” with a note of caution: Although it may seem like a simple process of zipping the window in and out of the convertible top, the actual process is much more difficult and takes quite a bit of patience. The procedure for replacing the window is documented in the sequence of photos accompanying this project.
With your new window in place, you’ll want to keep it pristine and unscratched. To minimize creases and scratches when the top is down, use some terry cloth towels to cover the window whenever the roof is lowered. BMW also has a factory rear window cover you can use to protect the window at all times. For cleaning the rear window, I recommend 3M Plastic Polish or the poly/glass rear window cleaner from Porsche (recommended for the Boxsters).
BMW has its own brand of cleaner (BMW part number 81-22-9-407-666), and BMW factory literature recommends Meguiar’s plastic cleaner #17 (BMW part number 82-14-1-467-128) and Meguiar’s plastic polish #10 (BMW part number 82-14-1-467-129) for heavier cleaning. All of these cleaners will do a good job of keeping your window clean and clear.
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Figure 1
Shown here is a brand-new aftermarket window replacement kit. The kit includes the pre-sewn window, a bottle of contact cement, and a starter zipper. Both aftermarket and OEM replacement windows may not fit as tight as the originals, depending upon the age and condition of your convertible roof.
Figure 2
Begin the process by popping open the roof to relieve tension on the rear window.
Figure 3
Removal of the rear window is straightforward. A: Using a plastic butter knife, or a plastic mechanical pencil, gently separate the roof fabric from the rubber trim. This rubber trim is sewn to the window and will be removed when the window is taken out of the car. B: From the inside of the car, locate and remove the zipper ties from the bottom center of the window. These two were added by an aftermarket installer and don’t necessarily reflect the original factory installation. Carefully pry back the tabs on these clips, and remove them from the window. C: Using your finger, gently separate the window zipper. D: Pull gently on the window, and the zipper should separate, allowing you to remove it from the car.
Figure 4
Insert the new window in place and mate the starter zipper. This is by far the most difficult part of the process. There are no end caps on the zipper teeth, so you may have to use a pair of needle-nose pliers to help get the starter zipper started. Begin by lining up and installing the starter zipper onto the two ends of the zipper teeth that point toward the left, if you’re sitting inside the car facing the rear. The starter zipper should easily make its way clockwise (from the inside of the car) around the edge of the window, using minimal effort (make sure that the fabric and/or window material doesn’t interfere with the starter zipper). The BMW factory manuals say that these teeth should be offset by no more than one in either direction, but in reality you may have to vary them by several teeth in one direction. If the zipper snags or is difficult to move, you may have to realign the zipper teeth on the start one or two teeth in the opposite direction. This was the most time-consuming part of the installation. I ended up varying the zipper teeth about seven teeth to the right in order to install the window with no wrinkles. When you are happy that the window fits properly, use the factory clamps (inset photo) to constrain and lock the zipper (BMW part numbers 54-31-8-134-598 and 54-31-8-134-599).
Figure 5
I found the most frustrating part of the whole process to be the actual zipping in of the window. You have to use a trial-and-error approach to get the window installed properly (it took about 35 tries for me). If the window isn’t lined up perfectly, you will get diagonal creases in the window when the top is up. To eliminate these, you need to release the zipper, then increase or decrease the zipper teeth offset. Moving in one direction or another will allow you to observe if the creases are getting worse or better. If the zipper won’t close without separating, you’re probably way off of the mark—the zipper should very easily make its way around the entire window.
Figure 6
As added protection against the zipper separating, I used two factory clamping plates to sandwich both zippers together. In this regard, I think that the BMW single-clamp design is not sufficiently strong to prevent the zipper from separating. Place one clamp on the outside and one on the inside, and tie them together with thin wire that you can push through the thread surrounding the zipper teeth. With the window properly zipped and installed, peel back the roof fabric and apply a thin bead of contact cement. Wait about five minutes for the cement to harden slightly—and be especially careful not to spill this on your newly installed window. Using a small awl, run it around the inside of the rubber seal, fitting the cloth fabric inside. Press down on the cloth to adhere it to the contact adhesive. The cement is very easy to clean up with a paper towel after it starts to become gooey.
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