Chrysler L/H Series Front Unirail Section Procedure

Chrysler Corporation's L/H models incorporate a cab forward design in the vehicle platform that provides a longer wheel base, wider track and increased interior room. The L/H series includes the Dodge Intrepid, Eagle Vision, Chrysler Concord, LHS and New Yorker models. This bulletin and photographs will specifically address the partial replacement of the left front unirail at a point directly in front of the mounting location for the steering gear crossmember. See Photograph 1.

Since the drivetrain assemblies in these vehicles are mounted longitudinally, there are certain parts that must be removed from the engine to gain the proper access needed for cutting, welding and refinishing during the procedure. Among the items requiring removal are the left side exhaust manifold and engine pipe, the transmission dip stick and filler tube, as well as the left front strut assembly.

The section procedure also applies to the right front unirail, although certain other mechanical components may have to be removed to facilitate repairs. Working room will be increased by removing the drivetrain assembly and engine cradle as a unit, instead of removing the necessary mechanical components individually.

The replacement unirails for these models are supplied in separate pieces rather than an assembly. Required components include the front side rail, closure panel and the bumper mounting reinforcement that must be welded to the inside rail. Caution: The mounting plate for the engine cradle bolt located inside the "C" channel of the rail is not included with the replacement rail, and must be purchased separately or transferred from the original rail and welded in place before the component is installed on the vehicle. See Photograph 2.

This particular section procedure uses a combination butt joint and overlap to attach the replacement rail to the existing structure.

A straight cut is made on the replacement rail while an offset cut is made on the existing portion of the damaged rail creating an overlap area at the section joint. Both the bottom and engine compartment side of the replacement rail "C" channel are butt welded to the existing portion of the rail with a root gap, using the forward portion of the "front floor rail" as a backer.

Measuring towards the rear from the front corners of the replacement rail, a straight cut is made 34 3/4 inches (882mm) through the "C" channel. See Photograph 3.

Plug weld holes are also drilled at specified points on the replacement rail where the overlap is located, as well as in the upper flange and the bottom portion of the "C" channel for additional welding points. See photographs 4 and 5.

The entire closure panel is inserted after the replacement "C" channel is properly positioned.

Prior to removing the damaged rail assembly, spot welds and two slot welds that attach the strut tower to the closure panel must be removed. The offset cut line is located 2.5 inches (64mm) forward of the leading edge of the steering gear crossmember. See Photograph 6.

Cut lines for the damaged rail are measured from the rear of the rail adjacent to the toe pan, towards the front of the vehicle. See Photograph 7.

Care must be exercised when making the cuts to avoid damaging the "front floor rail" which will be used as a weld backer and is an essential part of this vehicle structure.

During fit-up of the replacement rail to the existing structure, a 1/8 inch (3mm) root gap should be left on both the bottom and inboard sides of the butt joints for proper weld penetration to the backer. See Photograph 8.

After the closure panel is clamped in place and before any welding is begun, 3/8 inch holes are drilled in the former spot weld locations at the base of the strut tower where it overlaps the closure panel. A 5/16 inch drill bit is then centered in the 3/8 inch holes and drilled through the closure panel to allow plug welding of the two outer panels to the upper flange of the rail. (Note: The closure panel should be removed for drilling to eliminate metal burrs and shavings between the panels.)

All measurements should be verified after fit-up of the replacement components, prior to beginning welding operations. Follow the guidelines contained in the Welding Information section.

Welding Inforamtion

Prior to any welding operations, the weld site must be cleaned to remove grease and dirt as well as primers and paint; without removing factory corrosion protective coatings or grinding into the base metal. Do not remove any pre-existing 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 overlap area of 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 0.023/0.025 in. (0.6 mm) diameter which meets or exceeds the American Welding Society Standard (WAS-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 which can cause metal strength loss and panel distortion. The welding equipment must also be properly adjusted by making and testing practice welds on similar materials.

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.

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.