Monday, 31 July 2006 17:00

Volvo body innovations in structure require special repair technique

Written by I-CAR Advantage Online
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The second-generation Volvo C70 hardtop convertible (see Figure 1) is of interest to the collision industry for both its mechanical highlights as well as the body structure. The convertible features a retractable three-piece hardtop and side curtain air bags that deploy upward from the door shell. The pop-up rollbars for rollover protection are deployed using a pyrotechnic charge. 

Features of the body include hydroformed extra-high-strength steel upper A-pillars, an aluminum beam atop the door shell for better side and front impact protection, and different strength high-strength steels in the front structure for passenger compartment protection.

Retractable hardtop

The three-piece steel retractable hardtop opens and closes using an elaborate linkage system. An electric motor and four hydraulic cylinders fold the top into the trunk in 30 seconds (see Figure 2). The deck lid can be opened either from the back or from the front. Two sets of hinges are used. The retractable operation is controlled by a Convertible Roof Module (control module) located behind a trim panel on the right side of the trunk.

In the open and stored state, the hardtop is also considered part of the collision protection system. The layers of steel work with a double wall behind the rear seats to help absorb rear collision forces (see Figure 3). A horseshoe-shaped crossmember, also just behind the rear seats, further helps reduce intrusion into the passenger compartment in a rear collision.

Repairs on the hardtop are limited. There are procedures for scan tool diagnostics on the electronic control function, relieving hydraulic pressure, and replenishing the hydraulic fluid (a special fluid is required). There are replacement procedures for the headliners (a separate headliner for each of the three sections), electronic parts such as the position sensors, the roof links, and the entire roof if need be. There is also a procedure and adjustment specifications for misaligned roof links.


The upward-deploying side curtains are located in the upper section of the door shells (see Figure 4). One of them will deploy in a side impact on the side of

the collision. Both will deploy during a rollover. The curtains have extra stiff construction, compared to other curtain air bags, and deflate slowly for better protection during a rollover. There are also side impact air bags in the front seats for covering the chest and hip (see Figure 5).

Pop-up rollbars were a feature of the previous C70. The differences with this new model are higher strength and faster deployment. The rollbars on the previous model were deployed with a high-tension spring. The new C70 uses a pyrotechnic charge, similar to seat belt pre-tensioners. The backlite is glass, instead of flexible plastic, so the rollbars are equipped with spiked tips to break through the glass if there's a rollover while the roof is up. Each of the two rollbars is housed in a cassette that fits inside the seat back. As with the previous C70 model, replacement of the rollbar can only be done by replacing the entire cassette.

Other advanced restraint system features are common to many Volvo vehicles, such as an occupant classification system for the passenger seat, adaptive seat belt force limiters, and a pyrotechnic collapsible steering column.

Like other Volvo vehicles, only damaged or deployed parts are replaced after a deployment. The restraints control module is replaced after three deployments (a diagnostic trouble code is set) since its memory of collision information is full after three deployment incidents.

Body construction

The front structure of the C70 is built similar to the 2005 and newer S40 sedan, in that it is divided into deformation zones (see Figure 6). The more the collision forces approach the passenger compartment, the less the steel deforms. Four different strengths of steel are used: mild (up to 180 Megapascals (MPa) or 26,000 psi yield strength), high-strength steel (220-400 MPa or 32,000 - 58,000 psi yield strength), extra-high-strength steel (400 - 800 MPa or 58,000 - 116,000 psi yield strength), and ultra-high-strength steel (UHSS) (800 - 1400 MPa or 116,000 - 203,000 psi). Yield strength is the point where the steel begins to permanently deform.

Just as on the S40, there are front and rear bolt-on crashboxes that consist of two rail extensions and a bumper impact beam, the inner lined with UHSS alloyed with boron. The crashboxes can only be replaced as an assembly, not repaired.

There are sectioning procedures for the lower front rails (toward the front and near the cowl), upper rails (in the center and near the cowl), inner rocker panels (base of the B-pillars), rear rails, and trunk floor.

A convertible with its top down puts extra stress on the A-pillars in a rollover, so Volvo constructs the C70 inner A-pillars of hydroformed, extra high-strength steel, colored yellow in Figure 7. The inner A-pillars, which extend into the top of the rocker panels, can only be replaced in their entirety.

The hood and deck lid are aluminum. There are also hydroformed aluminum beams at the top of the door shells (also shown in Figure 6), designed to help with passenger compartment protection by leading the collision forces further back into the body structure in a front-end collision. The beams are part of the door shell and cannot be replaced separately. There are also door guard beams made of UHSS alloyed with boron that are laminated to extra-high-strength steel beams. The doors are designed to hook into the B-pillars and remain closed in a collision, allowing the doors to play an important role in side impact protection.

At the base of the B-pillars, a foam block serves as a collapsible, energy-absorbing "deformation box" between the B-pillars and the center crossmember.


The Volvo C70 convertible, newly redesigned in 2006, features the use of different grades of high-strength steels and hydroformed aluminum for passenger compartment protection. Mechanical highlights include a three-piece retractable hardtop, upward deploying side curtains, and pyrotechnic pop-up rollbars.

There are body repair procedures, including several partial replacement procedures, in the service information at the Volvo web site

This Advantage Online article first appeared in the I-CAR e-newsletter, which is published and distributed free of charge. I-CAR, the Inter-Industry Conference on Auto Collision Repair, is a not-for-profit international training organization that researches and develops quality technical education programs related to collision repair. To learn more about I-CAR, and to subscribe to the free e-newsletter, visit or contact I-CAR Marketing Communications Specialist Brandon Eckenrode at


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