Complete Underbody Assembly

This is commonly called the floor pan assembly and is usually composed of several smaller panels welded together to form a single floor unit. All floor panels are reinforced on the underside body stiffening members or cross members. Most floor pans are irregular in shape for several reasons. They are formed with indentations or heavily swaged areas to strengthen the floor section between the cross members and foot room for the passengers is often provided by these recessed areas in the floor.

On a four-door saloon this incorporates the A-post, the BC-post, the D-post and the rear quarter section. The side frames reinforce the floor pan along the sill sections. The hinge pillar or A-post extends forward to meet the dash panel and front bulkhead to provide strength at this point. The centre pillars or BC-posts connect the body sills to the roof cantrails. They are usually assembled as box sections using a top-hat section and flat plate. These are the flanges which form the attachments for the door openings. The D-post and rear quarter section is integral with the rear wheel arch and can include a rear quarter window.