I took the battery and battery platform out tonight and got way down there in the corner behind the battery...cleaned a lot of rust out and now I have a 3" hole which communicates with the inside of the front fender as well as the passenger footwell.

I think I've cleaned most of the rust off, and cleaned out the drain which caused the problem in the first place and I've sprayed the hell out of it with Rust Converter. I'm not looking for a super-duper auto restoration fix, just so I don't have water pouring on my wife's lovely feet.

Is there a tip or trick into getting up there with fiberglass? I don't want to close up the drain but, to be honest, I'm not really sure where it should go...

Shawnster,
One MB shop told me they see this "battery acid" rust problem frequently, but describing it to be more on the firewall under the battery. And that fiberglassing over it was their method of repair.
The corner is may be tight from the engine compartment, can you address the holes from the other sides?

shawnster,

First, there almost always is some residual dried acid left in the area, so mix up some baking soda with water and neutralize the whole area by rinsing with same. Once it's dry, you can attack the hole.

The problem with using a fiberglass patch is that the fibergalss resin doesn't adhere to the metal very well so it will eventually come undone, resulting in a leak again. It would be far better to make a fiberglass patch by applying fiberglass over the area after you've covered the area with masking tape and a coat of floor wax, to prevent sticking. Once the patch is cured remove the patch and the masking tape. Clean off any remaining masking tape adhesive, put some "Bondo" on the back side of your patch and slap it back in place. Now it will really stick and the patch is contoured to the area.

Get some of the spraycan black undercoating and spray the whole area and reinstall the battery tray once the undercoating has dried. Now wifie can always have dry toes.

Ben

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www.reproduce100s.com

A good auto supply place will have paint (usually black) that is rubberized and made specifically for use on battery trays. If you can't find it locally try Griot's garage or Eastwood. I used it on the battery box on my Alfa and it held up far better than the underbody paint I'd used before. Be sure the area is clean and 100% free of residual acid before you paint.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold

part of the problem is that I can't hardly get my hands down in there, even with the battery and tray out.

There are 2 major electrical/vacuum/thingamajiggies right in the way, and they disappear into the firewall so all of the resecting of rust and old metal had to occur with long-handled instruments of one kind or another.

I have much better access from within the cabin, up near my wife's right pinkie toe, in the corner.

You could try pop riveting a plate over the whole area from the inside, then going mad with the fibreglass paint and underseal from the outside - just make you smear all round the edges of the plate area, and raise it up with glass for some run-off. Hardly perfect I know, but you did say a full strip down would be impractical...

Does the water that leaks from the battery drain run to the passenger footwell or the driver's footwell. The reason I asked is I have water in the footwell on the rear drivers side. The battery is on the passengers side. I have cleaned out all drains except the one in the area under the battery. If the battery is on the right hand side can the water drain all the way over to the other side thus getting on the drivers side rear footwell. I wanted an opinion before I take the battery out tomorrow. Moreover, Doesn't the front sunroof drains run down the a pillar and onto the ground? When I poured water into my drains the water ran down the a pillars and in an area between the door and the front quarter panel. I don't think this is right is it?

The front drains from the sunroof do go down the inside of the "A" pillars as you described. However there are two more that I believe go down the inside of the "B" pillars, and these may be plugged.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

79300CD:
If your user ID indicates the model you are referencing (CD), you don't have A pillars (hence nickname "pillarless coupe"), which is why it drains out where you see it, and incidentally where it's supposed to be. I have helped a few people solve this problem, and it was never the sunroof drains, underhood drains, or battery drain. It was always the seal between the windshield glass and the gasket. This doesn't mean the other areas should not be checked. We fixed it by using a small plastic wedge that we ran around the winshield between the glass and the gasket, basically digging out debris/sand, etc.. Then we wet a rag with acetone and stuffed the wet edge in between the gasket and glass with the wedge and ran it around to clean the surfaces (repeated 3-4 times). After dry, we inserted the wedge to lift the gasket from the windshield, and followed the wedge with black silicone, pushing the gasket back down until a bead appeared on the glass. 24 hours later you can carefully cut away the silicone flush with the top of the gasket with a razor blade. Problem solved.

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1982 Mercedes-Benz 300CD
1982 Mercedes-Benz 240D - stick

The hood hinge pockets are also areas that can allow water to get into the cabin , if the windshield seal is leaking ( I've replaced the front and rear gaskets) you can see it on the inside of the windshield at the bottom corners, coming up and over the gasket. The rear window seal will drip into the trunk on the driver's side wheel arch, there's a drain hole on the bottom corner of the window opening . I was suprised to find no rust in either window openings , but I do have rust in the same areas as Shawn , as well as in the rear quarter panels . I've used layers of duct tape and tin-foil tape in hard to reach areas, then brushed seam sealer over it . Red Green would be proud

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Democracy dies in darkness, you have to kick at the darkness till it bleeds daylight

I forgot to mention this... There is hole in the bottom seat of the windshield wiper mechanism where the blade housing rests. Where does the water that enters this hole go? I sprayed water into this hole, and I could not tell where it was going. I never saw it leave the cabin anywhere. What's going on here? I don't want to ask too many questions about the same problem, but I have stopped driving my 300cd when it rains outside because I am tired of dipping out water.

Hi 79 300CD , if I understand your question properly , the water that enters the cowl area (at the wipers and grilles at base of windshield) drains out inside the engine compartment through two elbow shaped hoses on the firewall. Good luck

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Democracy dies in darkness, you have to kick at the darkness till it bleeds daylight