Battery Tray Repair

[mopedmaster]

I recently purchased a 1987 325iC. During the test drive, the passenger floorboard was dry as a bone. The previous owner drove it in the rain to the bank to sign over the title, and when I got home with it I noticed that the passenger floorboard was soaked. It seems to be in great shape outside of this:






From browsing around on various forum threads, it looked like it could be one of three things:

1. Elephant trunk is clogged
2. Battery tray is rusted out
3. Heater core needs to be replaced

The elephant trunk looked OK, a little debris in it but nothing that would completely block it.

So I pulled the battery... Definitely some rust/corrosion present there. Nothing that looked like it went all the way through the firewall, until I cleaned it off with a wire brush that is...



So after a bit more cleaning up I ended up with three large holes, one leading to the front passenger wheel well, one leading inside the passenger footwell, and one that was just through the tray in the engine bay.



The glovebox hinge was also completely rusted/frozen, and one of the hinge bolts sheared off from the firewall when I removed it..


Underside cleaned up:



Since I had no idea how long this had been occurring, I decided it would be a good idea to check the floor pans as well... They look great.





Drying it out:



So I talked to a friend who owns a body shop and he indicated that a metal patch with epoxy or fiberglass would be fine to fix this. I didn't like the idea of using epoxy to secure the metal sheet and I think the corrosion issues would just continue, so I opted to use fiberglass to do the repair. I purchased a $30ish bondo fiberglass kit from the local auto parts store and then cut templates.

I first cut small strips so I could build up and fill the back side of the battery tray (so that water doesn't settle there anymore), then I used a few layers of larger pieces to broadly cover the holes and finish it up.


Sanding it down:


Didn't really care if it was completely smooth, just as long as the rough spots were ground down and it was fairly even looking:


Next step was masking off:



Several layers of primer:


Several layers of basecoat:


Finished, with several layers of clear:


Also purchased some 3m rubber underbody spray to patch the corner of the wheel well (so fiberglass wasn't showing through):



Before:


After:



Total cost: $50 + 3-4 hours of time.

[mikewbd]

Curious, why not relocate battery to trunk?

[mopedmaster]

Thought about doing that, but...

1. I would have had to patch the hole anyway.
2. I want to keep it as original as possible
3. Not really keen on purchasing additional hardware and running cables from back to front.

[jeffw]

car is a beauty

[spike68]

That turned out great! your car looks good too. You good lucky with the floor boards.

If you put the battery in the back, I think you would have to remove the weight thats in its place. Why BMW put such heavy weight in the truck? not a clue. My only guess is better weight distribution. I removed mine just for the heck of it. My car does not squat as much when i step on the gas either. havent noticed much of a difference in handling. Maybe thats cause im not on stock setup.

[mopedmaster]

Thanks! My first time doing body work and working with fiberglass. It's a local (North Carolina) car and I'm the third owner (purchased for less than $3k), the last owner had it for 22 years. Most of the maintenance was done and I was provided with service records from 1991 - present. Maintenance wasn't to the level that I would do, but it's in really good shape for it's age body and interior wise. Just needs some general maintenance done, some really minor interior plastics swapped out, and a seam fixed on the passenger seat.

I will be digging in and doing the timing belt, drive belts, water pump, oil return tube, valve adjustment, etc this weekend and into next week.