Z3 M Coupe Rear Subframe Reinforcement: Part 2
In continuation of part 1, part 2 covers the reinforcement of the rear trunk floor.
Step 1: Weld chassis floor flat.
First, we stop drilled the existing crack near the battery tray box in the center of the floor. We attempted small spot welds around the bar stock used to level the floor and the crack. As this was our first time welding, there were some issues on the smaller gauge metal. We ended up figuring out the appropriate settings and cleaned this up substantially before completion.
Continuation of welding up the sheet metal we cut and hammered flat in part 1.
The sheet metal welded and sanded smooth. In the cavity, you can see where good penetration was completed by the welds on the diff ear reinforcement.
Step 2: Prepare and weld cavity reinforcement sheet.
The reinforcement bar for the cavity in the trunk floor is substantial and takes many plug welds. Here, it is clamped down and the holes are marked with a sharpie to prepare the metal for welding. We tried to remove as little factory e-coat as possible.
The dual diff ear reinforcements from the Randy Forbes kit were clamped to the bottom cavity in order to prevent bending the factory sheet metal.
Good weld penetration.
Step 3: Prepare and weld top chassis floor reinforcements.
Before the top plates were welded the inside of the cavity was masked off and painted with 2K epoxy primer to provide as much corrosion protection in the future as possible.
SprayMax 2K epoxy primer. 3680032.
After the cavity was sprayed with epoxy primer.
The back side of the reinforcement plates were painted to provide additional corrosion protection.
The top edge of the center plate was sanded back down to metal so a clean weld could be achieved when the top plates were welded. The cracked spot welds were then repaired by drilling them out. They were then welded and ground flat.
The top plates were clamped so they would sit flush against the center plate.
The top plates were designed so the holes would connect to the top of the chassis cavity when welded.
Spot welds completed and stitch welds going in tying in the top of the chassis floor to the bottom of the cavity through the center vertical reinforcement plate.
Step 4: Weld the frame rail reinforcements to the chassis and floor plates.
Peeking inside the frame rail as the frame rail reinforcements were spot welded.
Drilling the remaining popped spot welds on the driver’s side of the floor.
Reinforcement kit completely welded up.
Sanding the spot welds smooth in preparation of paint, seam sealer, and sound deadening.
Part 3 to include the completion of the reinforcement with seam sealer, paint, and sound deadening.
Wondering where this started? Check out Part 1 of the Z3 M Coupe rear subframe reinforcement. Check out the finishing step here.