Battery box replacement

Here's my monthly update (or so):

The battery box (front trunk) is done. Whew. It took awhile to get up the courage to actually do it, because it seemed so large in magnitude compared to the little patches I've been tackling before it. Once I cut into it though, there was no turning back. A complete picture log is available here.

I started by trying to read as much as I could about how to do it "right." There was a very valuable and encouraging entry in the "Nuts and Bolts" column of an old 356 Registry magazine, Volume 16, Issue 2. My thanks to Ron Roland for writing it and other helpful restoration articles! I also found some pictures of Tom's 356 Coupe battery box repair helpful. Go to Tom's Site and search for his journal entry on 04/12/2003. Last but not least, John Willhoit of Willhoit Auto Restoration has a lot of helpful pictures on his website.

After cutting away the front and floor, I attacked the sides. I used my replacement sheetmetal from Restoration Design as a template for how far back on the sides I could cut. The original sides are sandwiched between two other panels, where the gas tank floor and side of the frame meet, and there is no way to cut out that part. Therefore, the replacement side panels are a little shorter than the original panel. It is easiest to notch the replacement panels in the upper rear corners to accomodate the place where all these panels meet.

Fitting up the side panels literally took hours. I measured repeatedly to make sure that the two sides were the same height off the ground, were parallel with the rest of the frame, and were the proper distance apart, with no twisting. Lots of little snips and cuts in those upper corners. Finally, they were ready, and I punched holes in the flange with my flange/punch air tool so I could do plug welds. The top flange of the side pieces is installed on the inside of the frame member above it, rather on the outside as I have seen in some other cases. This is as it was originally. I also think this will be better for keeping water out of the seam.

Both sides were done in a similar fashion, tack welding in first, followed by plug welding the flanges on the top and rear. The welds were then ground slightly with a grinder, not totally flush so as to not weaken this important seam, and flat appearance isn't highly important since this area will be undercoated first.

Incidentally, I sprayed all overlapping surfaces with Bloxide Primer before welding. This is a weldable primer that supposedly reduces corrosion. I figure every little thing I do helps.

After finishing the sides, which took a couple of days of spare time, I took on the rear wall. On T-6 and C cars, the rear wall is made up of two pieces; one is long, and one is short. The short one is in front of the steering box and emergency brake pivot equipment. The side walls were minimally closer together compared with original because of the situation described above with overlapping panels. Because of this, the rear panel as delivered was too tight a fit. I decided to adjust the left side (small) piece to be a bit shorter. I unbent the 90 degree bend, cut off some material on the edge, and re-bent it a little bit closer to the left side of the car.

I actually was a bit overzealous in this change, I should have done about 1mm less. No matter, it all came out with clamps and swearing in the end...

Like the sides, the two pieces of the rear wall were painstakingly fitted up. Here, it was the top edge that gave the most trouble. There are lots of little bump-outs and other supporting stamps on the rear wall for strength. At the top, where the wiring harness is held up with tabs, is a nightmare. I cut my original wall all the way off, all the way to the top. If yours is better, you might choose to leave the top portion of the rear wall down to the section where the wall goes from vertical to the flange tilting forward to meet the gas tank floor.

I first tacked in the rear wall on the sides, and in the middle where the two parts meet. Then I tacked in the top. For the top seam on the larger piece, I plug welded in while lying on my back under the box, doing overhead welds. A major pain in the ass. For the short section, I drilled holes in the gask tank floor just above where the rear wall comes up, and plug welded in from the top. This was much easier.

An important note if you are doing this type of work yourself: Make sure you clamp everything tightly. Plug welds just don't work where there is a gap between the two panels being welded together. I borrowed a very large pair of vise grip clamps for some of the harder places to clamp.

The rear wall and sides complete, I took on the front piece. Now this piece was hard! My web searches didn't show too many cars where this piece was replaced. I think I now know why. The seam along the top of this piece is more or less moon shaped, and getting a tight fit between it and the piece above it where it is attached is difficult. Much more difficult than flat seams.

Tightly clamping these surfaces together while tack welding is essential. I lap-welded the front seam instead of plug welding, because of the slightly irregular surface. I wanted to make sure no water was going to creep inside this seam from the outside. Then, because I was at it, I did the same sort of weld on the inside. This, and the seams where the battery box sides meet the torsion arm cross member at the rear, are the only places I used lap-welds instead of plug welds on the battery box.

Nothing fits perfectly! Lots of clamping on the front edge of the side panels and the front panel to get a nice seam here to plug weld. When it was all done though, it was tight and pretty nice looking. I kept reminding myself that no one was ever really going to see this welding work. A few more days passed.

Finally, today, I did the finish welding on the front panel, and the floor. After all the rest, the floor was cake. The replacement panel comes as a rectangle with the battery hold-down bracket already attached. You have to notch the rectangle out to accomodate the step in the rear wall. I'm not entirely clear on why they don't do this automatically at Restoration Design, but I have a feeling it is because everyone fits up the rear panel a little differently, and they want to give you wiggle room.

After panel prep, I simply placed the floor on the flanges formed by the other four panels, and plug welded it in while holding it down with a big screwdriver. It worked well.

A couple of tips:

• When plug welding, use a higher heat setting/higher wire feed rate than you normally would for a seam weld. You need this to achieve good penetration because of the shorter duration of the weld time. I turn my welder up until I'm actually blowing through metal on the top panel, and then dial it back ever so slightly.


• Get lots of vise-grip style welding clamps. Especially the bigger kinds that you can't buy at Home Depot or Lowe's.


• Don't breath galvanized metal welding fumes (the battery box floor is galvanized). They will make you quite sick (zinc poisoning/"metal fume fever.") Hold your breath while welding, and have an adequately ventilated work environment.
  
• Patience, patience, patience! This took me a lot longer than I anticipated. The fitting portion of the work took more time than the actual welding. I'm more mentally prepared for what the floor pan replacement will entail now.

Speaking of floor pans: that's the next step. A small half-step before that is to invite some people over to help me lift the car onto my borrowed rotisserie, now that the front and rear bumper bracket mounting areas are solid! Stay tuned.

Posted by pbrown at February 27, 2004 10:03 PM