Replacement of the engine compartment lower rail assemblies has been improved through the use of a sub-assembly service part. Use of the sub-assembly service part simplifies the following actions:

The lower rail service part comes as a complete assembly, including all the brackets and the reinforcements. The bumper mounting brackets can be ordered and replaced separately.

Important: Loosen and protect the fuel and brake lines during rail replacement.

1. Support the engine and the transmission with suitable equipment.
2. Disconnect the engine and the transmission.

Important: Inspect the condition of the front suspension support where the crossmember is mounted. If the cagenut brackets have separated from the front suspension support, that assembly must also be repaired or replaced.

3. Remove all the other related panels and the components, including the suspension and the crossmember.
4. Inspect for damage.
5. Visually inspect and restore as much of the damage as possible to factory specifications.
6. Remove the following components as necessary:

•	The sealers

•	The sound deadeners

•	The corrosion materials




7. Locate and mark the factory welds along the lower flanges of the rail.
8. Drill out the factory welds.
9. Separate the lower rail from the floor extensions in the torque box area.
10. Locate and mark the remaining factory welds .
11. Drill out the factory welds.
12. Remove the damaged front lower rail. If the front suspension support is not removed, the damaged rail must be pried out.

Caution: Foam sound deadeners must be removed from areas within 152.4 mm (6 in) of where flame is to be used for body repairs. When reinstalling foam sound deadeners, avoid inhaling fumes as bodily injury may result.

Prepare mating surfaces.

1. Inspect for the proper fit of the lower rail service assembly.
2. On the service assembly, drill 8 mm (5/16 in) plug weld holes as necessary in the locations noted from the original parts.
3. Position the service assembly.
4. Inspect the fit of the service assembly using the body dimensions. Ensure the suspension support properly mates over the lower rail bracket.
5. Plug weld accordingly with frequent measurements in order to ensure proper fit.
6. Clean the welded surfaces.
7. Prepare the welded surfaces.

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

8. Prime with two-part catalyzed primer.
9. Apply the corrosion protection materials and the sealers, as necessary.
10. Apply the appropriate sound deadening pads to the floor as necessary in order to match the original sound deadening characteristics.
11. Reinstall all related panels and components.

Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

12. Install the suspension crossmember.

Tighten
Tighten the fasteners to 130 N·m (96 lb ft )