Friday, 31 August 2007 17:00

2007 Jeep Wrangler Sets Body-Over-Frame Design Trend

Written by I-CAR Advantage Online

The Jeep Wrangler was redesigned for 2007 (see Figure 1). The changes, especially the new features of the frame, are indicative of other vehicle maker trends in body-over-frame design. These include closed rail construction, hydroforming, less use of rivets, and crush zones in the frame rails similar to unibody construction.

Frame redesign

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 Figure 9

The changes in the Wrangler frame begin right up front, with a “compatibility crossmember” and hydroformed front rails. The compatibility crossmember is so-called because it is at the height of the bumper beam of a passenger car. There is a hydroformed tubular crossmember between the front rails. A transmission crossmember is bolted-on and easily serviced. There are seven crossmembers in all on the standard Wrangler, eight on the extended wheelbase of the Wrangler Unlimited. 

        The entire frame is boxed construction. The center portion of the frame is tubular, looking similar to hydroformed, but is actually roll-formed. The rest of the rail structure is stamped and welded closed “C” construction.

        There are four strengths of steel in the frame, from the 30,000 psi minimum yield strength mild steel for the crushable front rail tips to 80,000 psi minimum yield strength in the roll-formed center section (see Figure 2). High-strength steel internal reinforcements in selected areas in the frame are all 50,000 psi minimum yield strength.

        Some parts bolted to the frame thread into internal weld nuts. These include the transmission skid plate crossmember, fuel tank, and rear bumper bracket, among other parts. There are no rivnuts installed from the factory. Holes in the frame allow access to these weld nuts. Servicing damaged weld nuts requires cutting off the bolt and damaged weld nut with a cutoff wheel, and replacing the weld nut with a conventional M10 or M12 nut.

Body features

The unitized body upper rail structure has the fender and shotgun rail configuration also found on the Dodge Dakota, Durango, and Ram and the Chrysler Aspen. There is no hydroformed front lower crossmember, however, but a conventional style radiator core support (see Figure 3).

        The Wrangler has a four-door version for the first time. All power doors have a new feature called a “power carrier plate,” which is an isolator pad that serves as both a water seal and door cassette (see Figure 4). It houses the power door motor, glass regulator hardware, lock cables, latch, and wiring harness, among other parts.

        The procedure for removing the power carrier plate involves removing the inner trim panel, releasing the glass, disconnecting the wiring harness, removing a few bolts that attach the latch and door handle and finally the carrier plate itself. The carrier plate is removed straight out from the door from the interior side.

        The Jeep Wrangler is available with either a hard top or soft top. The hard top is sheet molded compound (SMC) (see Figure 5). There are a few repair procedures listed on the Chrysler LLC web site service information (www.techauthority.com) for damage to the hard top. The procedures include making a two-sided repair of a hole, repairing a fracture from the top side, straightening a sag, and diagnosing and repairing water leaks.

Frame repair procedure

There are procedures available in the service information for sectioning the hydroformed front frame tip and replacing the welded-on rear crossmember.

        The procedure for the front frame tip is for damage to the front frame rail confined to forward of the tubular crossmember. The cut line is through the crossmember, but the actual cut goes around the crossmember. The semi-circular shape on the end of the service frame rail is designed to fit around the front of the crossmember (see Figure 6).

        If one of the rails is damaged, it is very likely that the compatibility beam is also damaged. The compatibility beam is available as a service part. It is attached to the two frame rails with welded-on brackets. The bracket is removed from the undamaged rail. The other bracket, and the damaged beam, is removed when the damaged rail tip is removed.

        Instead of making the circular cut around the crossmember when the rail tip is being cut, it’s easier to make the first cut in front of the tubular crossmember (see Figure 7). The sectioning cut line can then be scribed and the cut made around the crossmember.

        The procedure calls for butt joint inserts on the top and bottom of the joint (see Figure 8). These are cut from the damaged rail tip. With the rail temporarily in position with tack welds, the service compatibility beam is fit-up. There are no specifications on the location, so side-to-side comparisons are required for its proper location. Alignment of the parts is verified with a three-dimensional measuring system. A GMA (MIG) butt joint is made around the complete sectioning joint perimeter, followed by welding on the compatibility beam.

        The rear crossmember is removed and replaced at the factory seams. The rear body mount fasteners are loosened enough to lift the body upward for access to the joint locations at the end of the rear rails. The crossmember is cut off using a reciprocating saw as close to the rails as possible. Each side of the crossmember is attached with seven GMA (MIG) fillet welds, which must be ground down after removing the crossmember with a reciprocating saw close to the welds. Before installing the service crossmember, shallow bevels are formed at the seven weld locations on each end for better weld penetration.

Passive restraint system

The Jeep Wrangler is equipped with multi-stage front airbags. The front seat belts are equipped with pre-tensioners, which are integral with the front seat belt retractors mounted on the lower, inner B-pillars. Wranglers made for sale in North America include an occupant classification system (OCS) on the front passenger seat. OCS parts include four strain gauges on the passenger seat and seat track position sensors on both the driver and passenger seats.

        There are two front impact sensors, located on either side of the radiator core support (see Figure 9).  Seat-mounted side airbags are optional. If the vehicle is equipped with side airbags, there will be a sewn tag with an SRS-AIRBAG logo on the outboard side of the front seat back trim cover.

        Side sensors, if equipped, are located behind the B-pillar trim panel neat the belt line. The restraints control module, or occupant restraint controller (ORC) is on a mount beneath the center console, on the floor pan transmission tunnel just rearward of the gear selector. This is a common location for Chrysler vehicles.

        After a collision when at least one airbag deployed, the deployed restraints are replaced. If the driver airbag deployed, the clockspring and steering column must also be replaced. If a front airbag deployed, the seat belt pre-tensioner did as well, requiring replacement.

        On vehicles with seat-mounted side airbags, deployment requires replacement of the seat back trim cover, seat back foam, seat back frame, and seat airbag jumper wiring harness. Jeep says that these parts will be damaged or weakened as a result of a deployment, which may or may not be obvious during a visual inspection.

        Jeep also gives a caution about multiple igniters on the front airbags. Typically, both igniters are fired and all potentially hazardous chemicals are burned during a deployment. However, it is possible for only one igniter to have fired due to an airbag system fault.

        Therefore, Jeep states that it is always necessary to confirm that both igniters have been fired to avoid the improper handling or disposal of potentially live igniters or hazardous materials. The service information contains a procedure that should be done with a scan tool to check for an undeployed igniter.

 

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