Lower Rail Replacement Full Replacement

Important: The lower rail service part comes as a complete unit, including all brackets and reinforcements.

1. Remove all panels and components necessary for access.
2. Restore as much of the damage as possible to factory specifications.




Important: Inner and outer sectioning templates are available for both the left and right rails. It is important to use the correct template when marking lines for cutting.

3. Align the appropriate inner and outer templates on the damaged lower rail and mark lines as indicated.
4. Cut the rail along the marked lines.
5. Remove the damaged portion of the rail.



6. Cut and remove approximately 5 mm (1/4 in) of the outboard and downward turned flanges of the lower rail.
7. Cut a 5 mm (1/4 in) gap approximately 5 mm (1/4 in) along the corners of the lower rail to create tabs.



8. Bend the tabs inward to allow the replacement lower rail section to fit over the original rail.
9. Weld all four edges together of rail at cut corners.

1. Align the inner and outer templates on the service part and mark lines as indicated.
2. Cut the service part along the marked lines. Discard the unused section.



3. Position the modified service part over the stepped tabs of the original rail, allowing 5 mm (1/4 in) of overlap.
4. Prepare all mating surfaces as necessary.
5. Apply 3M Weld-Thru Coating P/N 05916 or equivalent to all mating surfaces.
6. Stitch weld along the entire joint. When stitch welding, make 25 mm (1 in) welds along the seam with 25 mm (1 in) gaps between.
7. Complete the stitch weld along the seam.

Important: Prior to refinishing, refer to GM 4901MD-99 Refinish Manual for recommended products. Do not combine paint systems. Refer to paint manufacturer's recommendations.

8. Apply as necessary:

•

Sealers

•	Anti-corrosion materials

•	Two-part catalyzed primer

•

Top-coat

9. Install the panels and components previously removed for access.

Lower Rail Replacement Frame

Important: When servicing the lower rail and floor panel reinforcement, it is advised you use a fire resistant welding blanket to help avoid damage to the interior of the vehicle.

1. Remove all panels and components necessary for access.
2. Restore as much of the damage as possible to factory specifications.
3. Remove the following as necessary:

•

Sealers

•	Sound deadeners

•	Anti-corrosion materials




4. Drill out the factory welds along the lower flange on the floor pan reinforcement. Note that the flanges overlap the rails. Note the number and location of welds for installation of the new rail. Care must be taken not to damage the flange.



5. Separate the floor pan reinforcement vertical flange from the inside of the lower rail. Care must be taken not to damage the flange.
6. Turn the lower flange down on an angle away from the rail.
7. Drill out the remaining factory welds on the rail.
8. The lower portion of the wheelhouse at the rail must also be drilled out and removed.
9. With a flat chisel, loosen the adhesive (1) between the floor pan and lower rail by prying the rail away from the floor. Care must be taken to avoid damaging the floor.
10. Remove the damaged rail.

1. Prepare mating surfaces for proper fit of the new rail.
2. Turn the vertical flange forward to be welded to the new rail.
3. On the new rail, drill the same number of 8 mm (5/16 in) holes in remaining locations as noted from original rail.
4. Position the new rail in place and check for proper alignment.
5. Remove rail to clean and prepare all bare metal surfaces.
6. Prime surfaces in the same locations as the original adhesive using PPG's DP40, or an equivalent primer.
7. Apply GM Goodwrench structural bonding epoxy P/N 12345726, or equivalent.
8. Position the new rail in place and secure with temporary screws or clamps.



9. With the new rail in place, reposition the down-turned flange to the original location.
10. Plug weld in random formation until all welding is completed.
11. Remove temporary screws or clamps.
12. Clean and prepare all bare metal surfaces.
13. Apply the following as necessary:

•

Sealers

•	Anti-corrosion materials

•	Two-part catalyzed primer

•

Top-coat

Important: Prior to refinishing, refer to publication GM 4901M-D-01 GM Approved Refinish Materials for recommended products. Do not combine paint systems. Refer to paint manufacturer's recommendations.

14. Install the panels and components previously removed for access.