1955 Chevy Bel Air Project - Shoebox Structure

Next up is the radiator core support crossmember. It's alignment and placement is checked and set based off the engine/rack-and-pinion crossmember so when the car is assembled, the sheetmetal will line up properly on the new chassis.

The outer crossmembers are set in stages, front-rear-front-rear. As another crossmember is laid in, it's clamped in place, measured and checked for placement, then tack welded in position.

With all the outer crossmembers in place, the inner crossmember/X-member is built in pieces and tack welded in place. Fatman builds this piece with routing holes for the exhaust system so no matter how low to the ground the car is set, the exhaust won't be scraping pavement. The forward exhaust holes are oblong to allow for movement of the exhaust system for installation and removal. Placement of this structure is critical because the transmission mount bolts to the front, so there's no such thing as measuring too many times before tack welding everything.

Tying the two sides of the X-member together is this top loop and a bottom plate. This part of the chassis was specially designed to offer maximum rigidity for the frame, and the driveshaft loop in the center not only adds to that, but protects the passenger compartment from unexpected visits by the driveshaft in case anything fails in the drivetrain. The top loop also clears the factory tunnel on the Tri-Five body, so no body modifications are necessary.

With all the crossmembers in place and tack welded, the whole chassis is remeasured to make sure everything is aligned and located properly. Once it passes inspection, all the crossmember pieces will be fully welded to the framerails and the adjoining components.

Taking a break from the frame, one of the next steps is assembling the rear end housing. Fatman can use pretty much any rear end housing in its Tri-Five chassis as long as it meets the required width measurements. In our case, the requirement is a 59 1/2-inch hub-to-hub axle assembly. This will allow us to mount up to a 10-inch wide wheel/tire combo with 6 1/4-inch backspacing and 5 3/4-inch frontspacing in the rear without having to cut the wheelwells. The mounting brackets for the four-link bars are set in place on a jig, then the housing is dropped in. Once measurements and alignment are set, the brackets will be tack welded in place. For our chassis, we'll be using a Moser-supplied 12-bolt rear.

Moving back to the frame, the mounting points for the upper control arms and shocks are set in place, aligned, then tack welded.

Back on the rear end, the housing is rotated and aligned in the brackets so the pinion angle and alignment will be correct when mounted in the chassis. If the alignments are off here, then the car will never handle right and be an absolute bear when it comes to tuning the suspension.

Here, the mounting tabs for the rack-and-pinion unit are aligned and welded in place. This lower crossmember also serves as the mounting point for the lower control arms.

Next up, the transmission crossmember is clamped in so it and the engine mounts can be set up and secured to the chassis. When built, a Fatman chassis is set up for the transmission/engine combo specified by the customer. If you decide to change transmissions later on, the chassis has holes drilled for multiple crossmember mounting points. All you'll need is a new, correct transmission crossmember from Fatman, and you'll be good to go.

A dummy engine block and trans similar to what the customer specifies are set in place so the mounts can be properly positioned. Once everything's in place for the engine mounts and the measurements and alignments check out, they're tack welded on.

With the engine mounts set, the trans crossmember is located and then the mounting tabs are tacked in for drilling later.

These reinforcement tabs support the body mount, and serve as a mounting point for the frame-mounted, four-link suspension brackets.

Moving to the outside of the frame, the Fatman crew starts welding in the body mounting tabs. Fatman has all the measurements for the body mount locations on every Tri-Five model, so once you specify what body style you're using, the correct mounts are set in place. The Fatman mounts are much more substantial than the factory units, cutting down on body flex and adding more rigidity to the car's overall structure.

This is one of the rear sway bar endlink/body mounts. Because the location on the frame for these never changes, they can be mounted using a template and tacked in place.

With the sway bar mounts attached to the rear end housing, it's ready for the shock mounts to be tacked in, and the placement and attachment of the frame mounts for the four-link also attached.

The measurements checked out, so the four-link frame mounts are tacked in place. The mounts feature multiple locations so the suspension can be tuned as necessary.

With the bars set, measurement and placement for the crosslink mount is addressed. The crosslink gives the four-link design extra lateral strength for stability in cornering and other maneuvering.