New GM Underbodies – a Win for All

| February 6, 2015

Cadillac CTS rear view structure parts

Multi-piece rear floors aid invisible repairs

Shops that have repaired impacts to Cadillac’s new models, the ATS & CTS, are satisfied to see the trunk floor pans separated into four panels joined together with adhesive and resistance spot welds. Utilization of multi-piece floor panels means varying levels of collision damage can be worked out of a structure by replacing parts or assemblies at factory seams. This is a real improvement for technicians attempting to perform invisible repairs to collision damaged vehicles. Typically, rear hits involving the rails require sectioning or “splicing in” only a portion of a floor panel that may be five feet long and four feet wide. The new vehicles’ rear floors have natural joints separating the extensions behind the rear wheelhouses with the center floor pan. Each rear floor area drops down level with the rails for additional trunk interior space and to provide a “flat-floor underbody” to reduce air drag, which improves fuel economy.

The new models from Cadillac are built on a more “athletic” architecture, where each panel is “tuned for efficiency” from a mass and strength perspective. The new Cadillac underbodies’ natural seams allow for varying thicknesses/types of metal and the efficient sub-assembly of reinforcements where necessary. For example, the left side floor pan area in ATS & CTS is home to the battery, so floor extensions behind the rear wheel include braces and a tray to accommodate battery mass. Multi-piece floor panels in high-damage areas are a win for technicians, who can remove and replace portions of frame rails and/or floor panels when metal is kinked or damaged beyond repair.

Flexible designs with service in mind.

GM engineers creating this all new underbody were tasked with building a body structure that would be flexible to meet future vehicle designs. If, for example, a shorter or wider version of this underbody is necessary in future models, GM can modify this multi-piece platform by creating larger/wider wheelhouses or shorter/wider rear trunk floors. “GM will be utilizing a version of this underbody on a new high-volume Cheverolet in the near future,” says Bob Gollehur, product specialist for GM Aftersales.

So, if you haven’t seen these multi-piece floor panels in your shop yet, you soon will. When performing structural repairs, be sure to choose new Original Equipment parts and always be sure to follow the GM service prodecures. Service procedures in a limited form are available for no charge at and Electronic Service Information with links to air bag and mechanical repairs is available on a subscription basis at .

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Category: GM Parts News, The Technical Side