Replacing the Rear Quarter Glass On A Fiero GT Fastback by Chuck Murray of the Fiero Club Oklahoma - reprinted from the FCO News - Volume 3, Issue 12 - September 1998
The following text is the procedure for replacement of a rear quarter glass on a Fiero GT Fastback. The basic procedure was taken from a genuine GM shop manual for the 1987 Fiero, although it applies to the 1986 1/2 model GT also, the 1986 shop manual makes no mention of this procedure.
The procedure as outlined in the shop manual assumes that you will be installing the same glass, for whatever reason it may need to be removed. If you will be replacing the original glass with a new one I don't see why you would need to be so careful during the removal of the old one. Of course, you do not want to damage anything except perhaps the old glass. The fish line method of removal, as described in figure 8 on page 2J-5 of the 1987 shop manual, is nothing to get excited about and works just so so. If the fish method is not employed, then the glass must be removed by the exertion of hand pressure from the back side of the glass. Start on the back side, at the small end, and begin applying pressure along the vertical edge and move slowly forward at the top and bottom edge. What we are attempting to accomplish is the release of the double sided tape that secures the glass to the body. CAUTION ... If excessive force is applied to the glass, it may unexpectedly fracture resulting in bodily injury. Take your time and avoid damage to the car as well as protecting your own personal safety.
From my personal experience, and this is not spelled out in the manual, you must prepare the surface that the glass will be mounted to in the following manner:
Make a scraper approximately 1/2 inch wide X 1/8 inch thick X 6 inches long. The material may be wood or nylon plastic. The type of wood used may be pine, box wood, spruce or a similar soft wood. The material used to make a scraper should be just hard enough to maintain its shape when used as a chisel, but not hard enough to damage the paint or gouge the surface you are cleaning. Incidentally, a popsicle stick will also work very well for this procedure. DO NOT use any metal object, such as a screw driver, chisel, putty knife, etc. to scrape with. Those who choose to ignore this warning and use a metal scraper anyway, will be sorely disappointed with the results.
The general idea is to remove as much of the foam tape that is still sticking to the mounting surface as you can. How well you remove the old foam tape, using the wooden scrapper, will determine how much of the 3M™ General Purpose Cleaner #08984 will be required to remove the remaining adhesive and small pieces of foam.
As with any flammable material, use EXTREME CAUTION when working with the 3M™ solvent. This means no open flame, such as from a hot water heater, that is often found in or near the garage. NO SMOKING, and have plenty of ventilation in the work area. You may choose to perform this part of the operation out of doors. If you do work outside do not work in direct sunlight. You will find that the cleaner has a very high evaporation rate. Also, you never want to subject the paint to more abuse than is necessary, so the less solvent used the better. No matter how little solvent gets on the paint, the protective wax coat will be stripped.
One final word on the solvent, DO NOT substitute another solvent such as lacquer thinner, in an effort to save the $8.00 cost per pint for the 3M™ Cleaner #08984. Any other thinner that will attack the adhesive will also attack the paint, causing it to soften, wrinkle or lift off. To repair this damage will cost hundreds of dollars.
DO NOT use a substitute for the 3M™ products, (double faced tape and solvent), specified in the text from the shop manual. I can assure you that nothing else will work and provide the desired results. I know this to be true from the past experience of one damaged quarter panel glass and badly scuffed paint that resulted from a tape failure at 65 mph.
The specified 3M™ materials are available from auto body paint supply houses. If you have difficulty in locating a source of supply, the people at the 3M™ facility in St. Paul, Minnesota can help you, call 1-800-3MHELPS.
Use reasonable care when installing the automotive grade double faced tape. Reasonable care translates into not excessively handling the sticky face of the tape. This will ensure maximum bond strength of the tape to the body. Once the tape is properly aligned and secured to the body, the orange backing strip may be removed. Now comes the moment you have waiting for, the actual installation of the window glass.
The window must be carefully lined up, side to side and top to bottom prior to allowing the window to come into contact with the tape. Inspect the quarter window installed on the opposite side of the car if there is any doubt as to how it is supposed to fit the opening. It would be prudent to check this out prior to installing the double faced tape. Once the window contacts the tape, you are pretty well committed to whatever position the window is in. Patience and steady hands are the order of the day .
I hope this information is helpful, and good luck with your project.