The use of glass spacers has been (and still is) a common practice by a variety of auto manufacturers for OEM windshield installation. GM and Chrysler have used spacers widely from the mid-80's right into the 90's; Acura, Audi, BMW, Isuzu, Subaru, Volvo and others have all used them to some degree. They should not by overlooked, however, as an excellent method for windshield installation in today's replacement market.

Glass spacers, as their name suggests, provide spacing for the windshield during installation and subsequent urethane curing. Now assuming the full cutout replacement method is being used, correctly sized and positioned spacers provide excellent alignment of the glass in the windshield opening. This is essential for proper aesthetics (often aerodynamics) and minimizing the incidence of stress cracking.

A variety of sizes and configurations are found in spacer installations around the world. GM uses a number of different sized spacers, ranging from 5.5 mm to 12 mm (height); their triangular shape allows additional space for urethane contact in some cases. Chrysler consistently uses 1/4 inch (6.35 mm) in nearly all its applications; Audi may use two, even three different sizes in the same windshield opening.

Use Of Spacers In Windshield Replacement

There are three critical factors to consider in the use of spacers for windshield installation. Actually, these factors apply to both the OEM and replacement markets:

Size-
Auto manufacturers dimension spacers to provide proper glass spacing to the body in the glass opening. Few manufacturers use a urethane bead less than 4 mm high (cured). Thin beads simply do not provide a necessary cushion at the windshield perimeter; this can often contribute to an increased susceptibility to both stress cracks (unknown origin) and cracks resulting from minor impacts near the glass edge. We usually attempt to duplicate the size used in the specific OEM installation. A small stainless steel rule is valuable in checking spacer height.
Spacers can often be reused (may require some adhesive), however a good assortment of sizes should be on hand to replace those damaged during glass removal/opening prep. Keeping a log of notes on various installations can also be helpful when working with a previously replaced windshield - the spacers are often gone. Chrysler is easy with its 1/4" program; GM is a different story, with 5.5 mm/ Beretta, 7.0 mm/S-10, 8.0 mm/DW1067, 10.3 mm/some Cadillac models; hence, the necessity of the assortment.

Positioning-

The placement of the spacers is another key factor. Once correct size is established, we again try to duplicate the OEM layout. This is best determined after glass removal but before urethane trimming/opening prep. Surveying the original urethane bead (visually) will normally reveal the pattern of spacer placement. Keep in mind that spacers may be used in one case around the full perimeter of the windshield opening (Chrysler DW1118), while another application may use them only across the bottom (BMW, Audi); a third only top and sides, with a foam sealing strip providing bottom spacing (GM DW1067). Top and side spacers should be sufficiently inboard as to not interfere with proper urethane contact; bottom spacers must be placed where they will provide the proper urethane bead height and again, not interfere.

Spacer density-

The density of the rubber material used for windshield spacers is sometimes overlooked, even on the OEM level. The material (often PVC or urethane) should be sufficiently firm to support the weight of the glass during initial installation and urethane curing.
Foam dam, usually a relatively low density, provides proper support when used around the entire (or partial) perimeter; small sections, however, are insufficient as spacers. Chrysler spacers, though a foam type, are of a suitable density. Conversely, the density should not be too high either. Hard rubber spacers act as fulcrum-type points at the windshield perimeter; these contribute to stress cracks and reduced resistance to impact at those spacer areas, similar to the thin urethane bead condition. This is even more pronounced during the early stages of urethane curing. Spacer density should not exceed that of the cured urethane bead; ideally they should be composed of a rubber material with a Shore hardness of 42 or less. Use caution when substituting.

Spacers And The Urethane Bead

Sizing the triangular urethane bead is easy when working with spacers: The height of the bead should be double the height of the spacer.

Example 1: The S-10 DW943/1160 uses 7.0 mm spacers; we would cut our nozzle to form a 14 mm high triangular bead (8 mm wide at the base). In this case, a nozzle would be used with a guide pin, the urethane bead would be extruded around the perimeter of the glass, and using suction cups, the glass would be installed in the opening on a layout of 10 spacers (3 top, 3 bottom, 2 each pillar). The reveal molding is readily installed and an excellent fit is achieved.

Example 2: Chrysler minivan DW963/1118, 1/4" spacers; 1/2" high triangular bead, same 10 spacer format (some original installations may have used less). Molding fit/excellent, urethane contact/excellent, glass fit (spacing) to body/excellent.

Spacers can be invaluable in today's windshield replacement market. We are not suggesting that all installations warrant their use - many replacements are specifically designed for a sealant dam, self-spacing moldings, or even a combination of spacing methods. However, when properly implemented, spacers can assist in achieving the crispness of the OEM windshield installation, eliminating problems in replacement procedures, while reducing the incidence of spacing-related stress cracks.