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what would you do for this underside rust?


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You need to get in there with some pretty drastic work before it gets worse. It's not too bad but now is the time. 


The top shot - pull out carpets and remove all the sound deadener internal to the floor pans. Search on 'dry ice' you will find loads on the subject. This all need loose paint / under seal removed and any bare or rusty steel sanded back until shiny. Where you have small holes these should be poked to expose their edges and then cut out/ new steel welded in. This will be just coin sized patches so no technical challenge. 


The second shot is a lot more tricky. I suspect that you will have some fairly advanced rust in the rocker panel beneath the skin of the front fender. Hard to tell from pictures alone but you might be lucky and get away with taking all of the bolts out of the fender back and top, unfold carefully at the bottom and break the seal seal adhesion at the top. This should give you access to that area under the fender skin without junking the fender. You might be able to weld in some small patches underneath and then refit the wing. 


The textured surface on the rocker panel doesn't look factory to me and not very well adhered. I think I would strip the whole rocker to bare steel to see what's underneath.  


rtheriaque wrote:

Carbs: They're necessary and barely controlled fuel leaks that sometimes match the air passing through them.

My build blog:http://www.bmw2002faq.com/blog/163-simeons-blog/

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Take it to a good body shop. Have all the rust media blasted, cut out and replaced with new metal and painted with etching epoxy primer. Do it now before it gets worse. 

Andrew Wilson
Vern- 1973 2002tii, https://www.bmw2002faq.com/blogs/blog/304-andrew-wilsons-vern-restoration/ 
Veronika- 1968 1600 Cabriolet, Athena- 1973 3.0 CSi,  Rodney- 1988 M5, The M3- 1997 M3,

The Unicorn- 2007 X3, Julia- 2007 Z4 Coupe, Ophelia- 2014 X3, Herman- 1914 KisselKar 4-40

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What Simeon said.  What Adawil2002 said.  Good advice, both. 


It might look "a little rusty" and you might think "Maybe I could...maybe get by with..." However, deep mining and subsequent media blasting to bare metal, ESPECIALLY all around (all four dimensions of) the rocker panels, is mandatory if you an do it or 'ford it.  Likely a lot of metallic acne  in there doing its thing behind the scenes.  Advantage, during the process you can examine any needed work forward and aft the rocker panels (I needed it, too). See Simeon's 3rd paragraph for another wording of the same issue. 


Not particularly good news for you, I know.  Bummer.


Here is what I ended up having to do after I, too, found "...some visible rustiness...".

Photo 1:  Rocker panels looked "a little rusty" and not too bad...  Hey, what's the problem?

Photos 2, 3, and 4:  Things were bad.  Complete rocker panel replacement...and more.


Now, no rust, anywhere, and new strong metal doing flexing (actually, not flexing) it muscle.  Feel better knowing what is not going on where the sun don't shine.


Am looking forward to completed Euro conversion, body work, and paint around the end of November.  Now I know why you guys often mention "months" of body work and paint.


Larry Gray









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If your car is a '75, they're notorious for rusting around those front floorboard drain plugs.  They were to allow primer to drain out of the body when it was dipped in a primer vat at the factory.  That rust seems to be much more prevalent on '75s than any other year.  Suspect the factory used a different brand of sealer--that didn't.  


I had very good luck with using POR 15 paste (about the consistency of toothpaste or cake frosting) to patch very small holes like the one to the left of the drain plug.  Chip/clean back to sound metal and force the paste into the hole from both sides; it'll bridge a hole up to about 6-8 mm by itself; anything larger, use a little piece of fiberglass window screen.  Once dry, paint over it and you're good.  I field tested that stuff on my E30's rear fender lips (that rust just like 2002s) for three Ohio winters and no more rust at the repaired spots.  



'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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I'd fix that.

Scraper, wire brush, sandpaper- whatever it takes.


Once I had all the rust off, I'd coat it with my new favorite Rustoleum Professional spraypaint.


That'll hold it for a year or 4.


Now, if you find air behind some of that rust, you might want to pursue a bit more 

'replacey' regime.  I use a welder when that happens.


'Cause it happens to all of us.




"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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