This article was originally published Aug. 1, 2006. Some of the information may no longer be relevant, so please use it at your discretion.
The purpose of structural parts is often dictated by vehicle design. Some of these parts are designed to collapse at a controlled rate, while others are meant to resist collapse and transmit collision force when a vehicle is involved in a collision. Pillars are designed not to collapse, since their integrity affects many key areas of passenger safety.
The structural pillars on a vehicle simply have been named in alphabetical order. The most forward pillar, which has commonly been referred to as the windshield post or front door hinge pillar, is the A-pillar. The pillars, including the A-pillar, can have several design configurations.
Upper and lower as one
When referring to A-pillars many forget that the A-pillar not only includes an upper section (or windshield post), but also a lower section that includes the front door hinge location. For most vehicles these are all part of the same panel. The repair techniques and options for repairs often will differ based on the location of damage to this pillar.
The most basic design of the upper A-pillar is a two-piece, inner and outer configuration that may also include reinforcements at specific locations to add strength. These locations are usually at the upper and lower ends of the windshield location. For repairs this is the simplest type of construction to repair, section or replace. Often upper A-pillars may be three or more pieces to increase strength and at the same time complicate the repairs needed. We will look at these items later.
The lower section of the A-pillar generally has several reinforcements for the door hinge locations and may have other panels from the front structure or cowl that overlap. This too requires careful planning during the repair, sectioning or replacement of this panel.
Manufacturing variables
The A-pillar as with the other pillars may be manufactured and assembled individually and/or be serviced as a complete unit called a "uniside." At times the service parts may have several options to choose from. These options may include just the outer pillar, outer and inner panels as a unit, the outer panel with a complete or partial uniside, or inner and outer panels with a complete or partial uniside.
If the pillars are serviced separately, the Inter-Industry Conference On Auto Collision Repair (I-CAR) refers to these replacement panels as multi-part construction. This type of availability is becoming less common and is being replaced by the uniside construction method, which offers some key advantages over multi-part construction. These advantages include:
- Closer tolerances for better fit of surrounding panels because it may be stamped as one piece.
- Quicker manufacturing of vehicle versus building and assembling individual pieces.
- Less service part inventory than stocking individual pieces.
- Fewer seams and cracks for less wind resistance, noise and corrosion.
One possible perceived disadvantage is that when a part is serviced with a uniside only replacement part, much of the panel may not be needed. The cost of the uniside will be greater than an individual replacement panel.
Other designs and materials
For the most part A-pillars are normally made from stamped mild or high strength steels (HSS), but there are designs that utilize hydroformed steels and extruded aluminum with cast reinforcements. The latter is an example of the 2006 Corvette Z06, which includes an all aluminum space frame construction with bolt-in and adhesive bonded aluminum windshield opening frame. For any of these it is important to check manufacturer's repair information for proper procedures.
As with any structural repair, you should check to see if a specific procedure is available from the manufacturer or other research testing organization. Since this pillar is critical for passenger safety in frontal, rollover and side impacts, you should always carefully follow recommended and tested procedures when available. A resource I have found to be very beneficial is www.toolsfortechs.org. They will actually research the proper procedure for you.
I-CAR also provides general guidelines when repairing, sectioning or replacing A-pillars in the Structural Parts Steel Program (SPS02). Some of the key points include:
- Identifying proper location for replacement and sectioning.
- Considerations and limitation for repair versus replacement.
- Removal methods and tools.
- Working with two and multiple piece designs.
- Inserts and other weld joints.
- Welding procedures.
- Corrosion protection steps.
- Other considerations, such as foams, primers and windshield replacement.
The SPS02 program is part of a series of structural steel programs that should be standard for anyone in this industry to have completed before estimating or actually performing structural repairs. This article is not intended to replace all that is covered in the SPS02 course, but there are several important points that cannot be overstressed:
- Insert role and design
- Cut and Weld Locations
- Windshield Consideration
- Corrosion Protection
Many of these come into play during sectioning. As a general rule, there are likely to be fewer reinforcements inside an A-pillar at the center of the windshield opening than at either end. So this area is often the location of choice to section an upper A-pillar for both multi-part and uniside construction.
In addition, the area at the base of the lower A-pillar will often have additional reinforcements, foams and multiple panels attached to it. Often the A-pillar that is part of a uniside will be sectioned in the middle of the door opening where there is likely to be fewer reinforcements inside, as well. As to multi-part construction, the lower pillar is often replaced at the factory seams.
Insert role and design
One important consideration for the insert is that it must fit completely inside both the vehicle's original part side of the joint and the replacement panel side. Often inserts are "jambed" into the panel and proper welding into the insert cannot be performed because the insert has gaps. This also introduces the possibility of corrosion and a weakened joint.
To accomplish a proper joint the insert, when made of excess from the original damaged part or the new replacement part, must be cut in several areas to allow for it to fit properly. When the insert is properly installed and welded, the joint will typically be stronger than the original area, since it includes an additional layer of steel. This is okay since the A-pillar is not designed to collapse.
Even if the upper A-pillar has multiple inner layers there are several manufacturer and general guidelines for these designs. They will include cutting a larger outer panel cap that allows the sectioning of each inner panel. These techniques often use inserts for each layer as well.
For a final note on inserts, Toyota does not recommend the use of inserts when sectioning panels. They recommend an open-butt joint.
Cut and weld Locations
As mentioned earlier, the middle of the openings are often the preferred location to avoid inner reinforcements.
Also, the cut line should be between the original spot welds and not through them. The number of replacement welds should equal the original number and location of welds if gas metal arc (GMA) welding is being performed using the manufacturer's recommended plug weld size, which is generally 8mm or 5/16 of an inch. However if squeeze type resistant welding (STRW) is being used by an approved welder and as per a manufacturer's recommendation, the weld locations must be offset from their original location. In other words for STRW, the welds cannot be placed in the exact location as the original.
Windshield considerations
During the repair, sectioning or replacement of the upper A-pillar there are several considerations that must be followed or several safety issues will arise. One of the critical safety areas to be aware of for the upper A-pillar repair, sectioning or replacement is the windshield installation. The National Highway Traffic Safety Administration (NHTSA) develops Motor Vehicle Safety Standards (MVSS) for vehicles sold in the United States, or imported into the country.
The windshield and its installation method (original manufacturing) must be able to pass two performance standards, MVSS 212 and MVSS 216. These two tests, even though they are designed for vehicle manufacturers, become the standard for aftermarket repairs since we are by default contracted to restore the vehicle to "pre-accident condition."
MVSS 212
Commonly called the windshield retention test, the MVSS 212 requires the windshield to keep the front seat occupants from exiting through the windshield in a frontal collision. The test is performed at 30 mph into a fixed barrier. The windshield must maintain at least a 75 percent perimeter after unrestrained occupants hit the windshield. Most auto manufacturers work toward 100 percent retention as well.
MVSS 216
Commonly called the rollover test, the MVSS 216 requires the windshield and A-pillar area to withstand 1.5 times the weight of the vehicle directed downward at the front of the roof without crushing more than 5 inches during the two-minute test. Since rollovers vary greatly, this test is performed with a crushing panel applied to the front of the roof. The vehicle must be secured so the suspension is not a factor and all other windows are closed, such as sunroofs and doors.
MVSS 208
MVSS 208 is another standard that indirectly affects the replacement of windshields. This standard is designed for passenger airbag deployment, but in the specification it acknowledges that the passenger airbags designed to rebound off the windshield for proper positioning will do so with the force of 300 lbs. per square inch. Therefore, for proper placement of the passenger airbags the windshield must be able to withstand this force without being pushed out.
All metal work areas where an adhesive will be applied should be "metal finished." In these areas no plastic filler should be used since its adhesion characteristics are lower than the urethane adhesive. Also during refinishing the pinchwelds should be primed with the appropriate epoxy primer, and not topcoated or cleared. Again the paint system could be considered the weakest link.
If a seam sealer has been used by the manufacturer where the adhesive will be applied to bond the glass, it should be replaced with the adhesive that will be used to bond the glass, not our typical seam sealers.
Again this article is not designed to be inclusive of the proper replacement of bonded glass, but the key considerations for A-pillars in the glass adhesive areas are:
- No plastic filler
- Epoxy primer only
- No topcoating or clearcoating
Corrosion protection
The design of the A-pillar may require careful planning to restore corrosion protection after the repair, sectioning or replacement. This may include the replacement of foams, adhesive bonding materials and seam sealers as well.
One general rule is: If corrosion protection cannot be restored then you have selected the wrong area to section. It is critical that after any repair the corrosion protection can be completed to ensure that the backside and inner areas will not fail due to corrosion.
Part of the process includes applying an epoxy primer to the inside of the panels where welding, straightening and repairs have damaged the original coating; apply foams where required after the primer has cured; and applying anti-corrosion compounds (rustproofing) after the refinishing has been completed. This process, especially with the use of inserts, is often misunderstood and not performed completely.
Another corrosion protection step may include the use of a primer on bare metal areas before welding. There are several considerations for the use of these commonly called weld-thru primers. First, they are not required for coated steels including factory e-coat, galvanized or galvanealed panels. Also, these primers are not recommended by Daimler-Chrysler on any of their vehicles, and Ford Motor Company recommends the use of PM13A rather than conventional weld-thru primers. The role of these primers is often misunderstood by many in the industry.
Lower A-Pillar sectioning
For the lower portion of the A-pillar, manufacturers recommend against cutting through the hinge mounting areas and the corners of a uniside panel. Often, as mentioned before, these uniside panels are sectioned through the middle of the door opening. Some manufacturers have locations horizontally between the upper and lower door hinge mounts. Otherwise often for multi-part construction designs the factory seams are used at the base of the pillar at the rocker panel and cowl.
At times the inner panels will require repair and replacement as well. This may require the removal to additional overlapping panels. Again, plan for proper corrosion protection, foams and seam sealers.
Conclusion
This article cannot possibly provide complete step-by-step instructions on dealing with all the different designs for A-pillars, however some general guidelines have been provided. The detailed information is available from many sources, including the vehicle manufacturers and I-CAR.
The most important point of this article is to get the up-to-date information before you begin the repairs, sectioning or replacement of structural parts, including the A-pillar. Information today is very vehicle year-and-model specific, so what you may have heard or been taught five to 10 years ago may very well have completely changed. Don't allow this to compromise the safety and durability of the automobiles we repair. It is a costly error you don't need to experience.
