Research Bulletin 1990-6
Research Bulletin 1990-6 |
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This Research Bulletin deals with sectioning procedures for the lower unirail on Ford Taurus and Mercury Sable model vehicles. The purpose for this procedure is to lessen the amount of vehicle disassembly and the accompanying disruption of the manufacturers factory applied corrosion protection.
The lower unirail on this model vehicle is a large, complex member of the structure that is attached to a number of other structural components. This particular unirail is serviced as an assembly that includes both the strut tower and apron panel, Photograph 1.
If only the front portion of the rail is damaged, a considerable amount of labor and vehicle disruption can be saved by replacing only the front portion, rather than the entire assembly. This procedure is appropriate when the assembly has sustained heavy or moderate damage. The damage must be confined to the area in front of the section joint, (Photograph 3) and only minor component alignment is necessary behind the section joint.
Because of the manner in which this unirail is serviced, and the accompanying disassembly associated with repairs, development of a sectioning procedure was initiated which included both component and full vehicle crash barrier testing, Photograph 2.
This research bulletin will address a procedure that uses inserts and a corresponding butt joint rather than the usual Tech-Cor overlap method of attachment. The reason for this variation is that the configuration of this particular rail does not lend itself to our minor overlap procedure in the section joint area, Photograph 3.
Since the lower unirail on this model is manufactured from heavy gauge steel, and has a narrow, tapered cross-section, it is extremely difficult to split the exposed corners of the rail to achieve the appropriate overlap.
This procedure can be performed on both Taurus and Sable model vehicles from model year 1986 to the present and can be performed with the drivetrain in place.
The repair differs slightly from the section procedure developed by Ford Motor Company as outlined in the Taurus/Sable Body Collision Repair Manual, and was approached in this manner to aid the repair technician with fit-up and assembly procedures.
By using a butt joint with inserts, this procedure can be accomplished in an efficient manner, with new or used structural members, while leaving the drivetrain in place. The small inserts, Photograph 4 aid in the welding operation by acting as back-up material at the butt joint, and are fabricated from the remaining portions of the replacement rail after the section cut is made.
Normal safety precautions must always be observed when working with collision damaged vehicles and related repair equipment. Prior to replacement of any front unibody rails, the following procedures should be completed to allow for proper sectioning techniques:
When the rail section procedure is completed, the remainder of the assembly and reinstallation of other unibody parts can be completed. All adjoining seams and welded areas should be prepared as described in the WELDING INFORMATION section of this bulletin. Corrosion protection including the refinishing of replacement components should be performed as outlined in Tech-Cor Bulletin 1986-7, RESTORING CORROSION PROTECTION DURING VEHICLE REPAIR.
Read this bulletin completely before making any section cuts on the damaged or replacement rail. All measurements should be treated as Guidelines Only, ongoing manufacturing changes may affect the placement of holes during component stamping operations.
Left Lower Unirail Section Procedure:
Measuring and scribing operations are performed on the outer portion, or wheelhouse side of the lower rail, since this area provides greater access.
The cut line for the damaged rail is scribed 2 inches in front of the leading edge of the elongated hole, measuring towards the front of the vehicle, Photograph 3. This hole is elongated on the outer portion of the rail and round on the inner portion. The use of a 90 degree square is recommended since the base can be positioned on the upper ledge of the rail, while the cut line is scribed along the perpendicular portion of the square.
After the scribe line has been marked on the outer portion of the rail, the cut is performed through the entire rail section to obtain a parallel surface. The replacement rail section is cut at the same location as the original damaged rail.
Section Inserts:
The inserts used for this procedure are fabricated from the portion of the replacement rail that remains after the section cut is made.
Photograph 4 shows a cross-section of the rail used to fabricate the inserts. After the cross-section is separated by removing any spot welds, both upper and lower flanges are trimmed to form inserts with a 90 degree angle.
The two inserts are each approximately 1 inch in width, and are installed in the existing portion of the original rail. Prior to installation of the inserts, two 5/16 inch holes are drilled in both the inner and outer portions of the existing rail with a centerline approximately 1/4 inch rearward of the cut line. The inserts are then clamped in place, allowing 1/2 inch to protrude from the open end of the rail, Photograph 5. Plug welding can then be performed to secure the inserts to the inner and outer portions of the rail.
After the replacement rail has been cut to the specified length, it is positioned over the inserts and butted against the existing rail. Care must be taken to make the best possible butt joint allowing a 1/16 inch root gap between the new and existing rails. This fit-up procedure is simplified since the inserts act as guides for proper positioning of the replacement rail section.
When the correct measurements have been verified, plug welds may also be performed between the replacement rail and inserts. The entire section joint is then butt welded per the procedure described in the WELDING INFORMATION section of this bulletin.
Photograph 6 shows the completed rail section prior to refinishing and corrosion protection operations. Following these procedures, Tech-Cor re-instrumented the vehicle and subjected it to a second 15 mile per hour offset barrier crash to test the repair. The performance of the sectioned rail during the second impact achieved equivalent performance to that of the first crash.
Prior to any welding operations, the weld site must be cleaned without removing factory corrosion protective coatings or thinning the base metal. Do not remove any preexisting galvanized coatings. Do not use an oxyfuel (oxyacetylene) gas torch. After cleaning, a weld-through coating must be applied to all bare metal in the weld sites. All welding should be performed with a M.I.G. welder (Metal Inert Gas, now called G.M.A.W. or Gas Metal Arc Welding). Welding wire should be either 0.023" (0.584 mm) or 0.025" (0.635 mm) diameter which meets or exceeds the American Welding Society Standard (AWS-E-70S-6) with a mixture of 75% argon and 25% carbon dioxide shielding gas. Do not concentrate all welding efforts on one area, but alternate sites so that each welded area has time to cool down before the welding is continued. All continuous welds must be made in 1/2" - 3/4" (13-19 mm) increments which helps to minimize heat build up and panel distortion. All plug welds are made by welding around the edge of a 5/16" (8 mm) diameter hole. The welding equipment must also be properly adjusted by making and testing practice welds on similar materials.
The
information provided in this bulletin is for educational purposes only. Although
every effort has been made to ensure the accuracy of the information contained
in this bulletin, Tech-Cor assumes no responsibility or liability for
any repairs performed using information from any publication issued by Tech-Cor.
Any person performing repairs must determine whether any suggested or recommended
procedures or repairs are suitable or appropriate for the particular vehicle
being repaired. The repairer remains solely responsible for such determination,
as well as for the proper completion of the repairs.
Reproduction of this bulletin is not permitted without the written approval
of Tech-Cor.
Tech-Cor, LLC, Wheeling, IL
© 1990 Allstate Insurance Company
All rights reserved.
