About I-CAR - Current Events/News: e-newsletters: Advantage Online: March 17, 2008

Figure 1 - The Chevrolet Cobalt has been available since model year 2005.

Figure 2 - The non-painted portions of this front end prop show the service upper tie bar and the two partial upper side rails.

Figure 3 - The partial upper rail sleeves over the end of the tie bar.

Figure 4 - The replacement three-sided upper rail portions are pre-sleeved for the butt joint into the existing upper rail.

CHEVROLET COBALT UPPER TIE BAR KIT AVAILABLE

The body design of the 2005 and newer Chevrolet Cobalt (see Figure 1) uses a layered build sequence in the front structure. The upper outer rails are sleeved over the upper tie bar, which is basically the radiator core support. General Motors has a replacement service kit and procedure for replacing the upper tie bar and portions of the upper outer rails.

The upper tie bar kit includes the upper tie bar and the two partial upper side rail service parts. The kit can be seen in the front prop assembly shown in Figure 2. A close-up view of the passenger side in Figure 3 shows where the upper rail overlaps the ends of the tie bar. The recommended sectioning location is measured forward from a hood hinge mounting hole, also visible in Figure 3. Looking at the assembly prop on the driver side in Figure 4, one of the replacement three-sided upper rail portions can be seen. The parts are pre-sleeved, providing a built-in backing for the butt joint at the sectioning location.

Depending on the extent of the damage, the recommendation is to replace the tie bar along with at least the two partial upper side rail service parts. If one or both of the upper rails have non-repairable damage beyond the sectioning location, the recommendation is to replace one or both of the entire upper side rails, which are also available as service parts. This article will describe the procedure for using the replacement upper tie bar kit with the two partial upper rails.

The GM procedure requires cutting each upper rail portion off and then removing the spot welds to release the upper tie bar, rather than removing the assembly at one time. Locate the cut line on each upper rail by measuring 225 mm forward from the center of a hood-hinge mounting hole. After removing spot welds forward of the scribed line, and making the cuts at the scribed lines, the upper outer rail portions can be removed. The spot welds holding the upper tie bar assembly can now be drilled out and the damaged tie bar removed.

The replacement upper tie bar is installed using GMA (MIG) plug welds, since there is no two-sided access for replacement spot welds. The plug welds are made in the same locations as the original spot welds. If the original locations can't be determined, space replacement 8 mm (5/16") plug welds every 40 mm (1½"). GM recommends weld-through primer on all of the bare metal mating surfaces.

Since the upper rail portions are pre-sleeved, it’s not necessary to fabricate inserts for the butt joints. The pre-sleeved ends are simply inserted into the end of the cutoff rail ends, leaving a 1.5 mm (1/16") root gap for the butt joints. GM also recommends plug welds where the pre-sleeved ends fit into the rail. Drill six plug weld holes into each rail end, two on the top, side, and bottom.

Replacing the upper tie bar on the 2005 and newer Chevrolet Cobalt requires a service kit and special procedure. Included in the kit are portions of the upper outer rails, which sleeve over the ends of the upper tie bar, and are pre-sleeved to fit into the ends of the existing upper outer rails. The complete procedure for replacing the upper tie bar is available free of charge at the GM web site for technical collision repairs: www.techinfo.gmgoodwrench.com.

More information on this type of layered construction and repair can be found in the I-CAR Live “Steel Unitized Structure Technologies and Repair (SPS07)” training program.

For comments or suggestions on the Advantage Online, please contact I-CAR Senior Instructional Designer Bob Jansen at bob.jansen@i-car.com.

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