1997-99 Ford 4x4 Truck Frame Horn Replacement

Front Frame Horn Replacement for:
1997-99 Ford F-150/250 4 x 4
1997-99 Ford Expedition 4 x 4
1998-99 Lincoln Navigator

Introduction

This bulletin will detail a sectioning procedure for replacing the front frame horn on 1997-99 Ford F-150/250 4x4 pickups, 1997-99 Ford Expedition 4x4 and 1998-99 Lincoln Navigator sport utility vehicles. Sectioning of a damaged frame horn can be performed to avoid replacing the entire vehicle frame. Refer to photograph #1 for close-up view of left front frame rail damage.

This bulletin references the left side of Ford F-Series light duty 4 x 4 pickups, Expedition 4 x 4 and Navigator models only. Super Duty F-Series vehicles and 4 x 2 models are not covered by this procedure.

Procedural Notes

Prior to beginning this procedure, the vehicle frame should be checked for proper structural alignment.

Certain mechanical components must be removed to gain access for cutting and welding operations. The radiator will need to be removed, although the core support can be left in place. The air conditioning condenser (if so equipped) will also need to be relocated. If undamaged, the refrigerant system can remain closed and intact throughout the repair procedure. Finally, the steering gear box and remote oil filter assembly will need to be unbolted and temporarily moved aside. Refer to photograph #2.

Due to the thickness of the mild steel frame rail, proper welding equipment and procedures must be utilized to ensure sufficient weld penetration and strength.

A continuous welding technique should be used for all four sides of the rail with full fill of the 4mm (5/32 inch) root gap between the base metals expected in one continuous welding pass. Slight weaving from one side of the joint to the other may be necessary for complete penetration of the filler metal into the base metal sections and the weld backer insert material, as well as completely filling the root gap. Cosmetic completion may also be necessary.

Practice welds should be made on the discarded portion of the frame horn and tested for adequate weld penetration prior to welding the replacement frame horn section into position.

Repair Sequence

1. Using a wax and grease solvent, remove the rustproof coating from the outside surfaces of the frame and the replacement frame horn within approximately 51 mm (2 inches) of the cut-line.

2. The damaged portion of the frame rail will be removed along a line located between the radiator core support mounting bracket and the forward mounting holes for the steering gear box. Scribe a line on both sides of the damaged frame rail through a point 30 mm (1 3/16 inches) forward from the top bolt hole and a point 35 mm (1 3/8 inches) forward from the bottom bolt hole. Refer to photograph #3. Next, connect the ends of each vertical scribe line across the top and bottom of the rail. A continuous line should now be scribed on all four sides of the frame rail forming the cut-line.
   

3. The replacement frame horn should be removed along a similar cut-line 34 mm (1 11/32 inches) from the top bolt hole and 39 mm (1 17/32 inches) from the bottom bolt hole. The difference in dimensions between steps #2 and #3 will result in a 4 mm (5/32 inch) root gap.

4. Use a reciprocating saw or cutoff wheel to remove the damaged and replacement frame horns. Do not cut directly along the scribed line. Leave enough material in front of the scribed line to allow the edge to be ground back exactly to the line. This procedure is necessary to insure a precise root gap between the vehicle's original frame and the replacement frame horn section during fit-up.

5. Due to the configuration of the rail box section at the repair joint, a 13 mm (1/2 inch) weld backer insert must be fabricated from a similarly shaped portion of the undamaged frame. Refer to photograph #4.
   

6. Remove the rustproof coating from the inside surfaces of the frame and the replacement frame horn at the section joint location and all surfaces of the weld backer insert. These procedures will help ensure a strong weld by minimizing contamination. Refer to photograph #5.
   

7. Carefully grind a 30 degree bevel along the scribe line at the cut edge, on all four sides of the original and replacement frame. This procedure will form a "V" with a 4 mm (5/32 inch) root gap at the inside surface of the frame material which contacts the weld backer insert. Refer to illustration #1. This weld joint preparation will allow for sufficient weld penetration into the backer plate while fusing the replacement and original frame materials together.
   

8. Remove any foreign material or debris (e.g., weld splatter and cutting burrs) from the existing frame and the replacement part within 13 mm (1/2 inch) of the repair joint to allow easy and proper fit-up during assembly.

9. On the vehicle frame at the cut-line, cut or grind a 6 x 6 mm (1/4 x 1/4 inch) notch at each corner. Install the weld backer inserts halfway into the existing frame and tack weld them into place at the notched areas. Refer to photograph #6.
   

10. Install the replacement frame horn over the backer inserts. Clamp the replacement frame horn section securely in place, leaving a consistent 4 mm (5/32 inch) root gap between the replacement frame horn and the original vehicle frame. Tack weld the replacement section in place. Refer to photograph #7.
    

11. Re-check all measurements to verify that the replacement frame horn is properly positioned. Following the procedures described earlier in the Bulletin, weld the upper and lower horizontal joints from corner to corner. Then, weld the inner and outer vertical joints from corner to corner.

12. After all welding is complete, grind the weld material flush with the side rails. Be careful no to grind into the base materials. Refer to photograph #8.
    

13. Restore the original corrosion protection by re-coating the repaired area and the replacement frame horn, both inside and outside, with a wax-like, creeping rustproofing material. The enclosed portion of the section joint can be easily reached with a typical rustproofing applicator spray wand.

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.