Connecting the bottom of the rear quarters to the rest of the car, of course, are the rocker panels. Once the pieces were separated from the door, front fender, and rear quarter bottoms, and rejoined as one, the IFG rockers provided a continuous connection between the wheel housings:
The rockers ended up being surprisingly wide making the door sills nearly 11” wide compared to a Fiero GT’s, which are closer to 5”. Being made of fibreglass, I couldn’t risk someone sitting or standing on them without adding some structural support from within. After taking a few measurements I decided to build the steel “out-rigger” system shown in red below. The view is a cross section of the Fiero floor pan at the door opening area as seen from the rear:
The blue lines represent the cross section of the steel Fiero floor pan and rockers. The OEM steel rockers are formed from a stamped “C” channel boxed-in with a flat plate on the inboard side. The green line represents the F355 fibreglass rocker, and the red shows the planned support structure comprising inboard and outboard square steel tubes triangulated to the top and bottom of the OEM rocker channel.
I wasn’t able to make the support structure the full width of the fibreglass rockers over the whole length because of the rocker air scoops. The scoops took up a fair bit of real estate inside the rocker panels, especially towards the rear where they were deepest. The arched line drawn on top of the fibreglass rocker shows the outline of the scoop inside:
Knowing the path of the scoop, I fabricated the main rocker supports by cutting some 1” square tube for the inboard portion and ½” tubing for the outboard. The ½” tubing was easily bent using my foot and a bit of pressure. Then I started connecting the two tubes by adding 1” wide x 1/8” thick steel bars between them:
The upper portion of the support looked like this once fully framed and welded:
The next step was to level, square up, and weld the support to the OEM steel rocker channel, then weld the triangulating lower braces to the bottom like this:
Here’s the completed rocker support structure:
To fasten the fibreglass rocker to the support, I needed to consider attaching it along both upper and lower edges. The upper edge was simple: I drilled some evenly spaced holes in the 1” square tube and swaged some threaded inserts into them:
The lower attachment point was a bit more work. A simple “L” shaped flange extension (see arrow) welded to the integral OEM spot weld flange was what my plan called for:
The problem was that GM welded a few obstructions to the flange that got in my way. The plates originally served two purposes: hard points for side-jacking the car, and; the upper half of a coolant tube clamp.
GM also welded a smaller coolant tube clamp towards the front of the car as well… but it too was in the way of my plans:
Since I didn’t need to run coolant tubes to the front of the car anymore, I decided to drill out the spot welds holding the offending pieces to the tunnel. I’ll have to remember not to let anyone lift the car from the stock side-jacking points:
With the plates/clamps removed, I cleaned up the tunnel with a wire wheel and sprayed some self-etching primer to tide the rust over until I can get the car on a proper hydraulic lift. I’ll also address the holes in the floor pan at that time too:
The next step was to cut and bend some 18 gauge steel strips into angles, and pepper them with threaded inserts:
For now I made these flanges removable to give me a chance to properly treat and paint the tunnel later. Here’s the passenger side lower rocker mount bolted in place:
The last thing to do was slip the fibreglass rocker into place and screw it to the upper support with countersunk machine screws…
… and to the new lower rocker flange along the bottom:
And, Ta-dah! Removable, supported, adjustable, mounted, one-piece rockers:
The upper surfaces of the rockers are still only made of masonite, so there’s a lot more work to do to them. I’ll cover their replacement under the next phase once I’ve finished mounting the rest of the body panels.