Rust stop approach

JHZR2

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This is the underside right above where the exhaust is on my 91 BMW 318i. Unfortunately it is also where the transmission mount support bolts to the body. I dont think the trans support actually supports much, looking at how it is held to the body of the car, machine screws are just slid in a track with their heads held in the track, and then the bar held to that with a nut. Not much to it. Hopefully the forces are OK and the right hand rule is in my favor (this rust is on the PS of the car, BTW). My approach is this: -scrape all loose rust to leave a rough surface (done) -coat surface in Eastwood rust stopper (done) -paint surface with Eastwood rust encapsulator -lightly sand and paint with another regular paint (possibly rust oleum epoxy spraypaint because I have it) -there is a thin sheetmetal piece that goes along that same area - doesnt seem to be a heat shield, but is OE fit and causes a gap right at the point where the rust is that lets water sit - and rust form. I was thinking of masking the exhaust pipe and then spraying in the gap with rubber undercoating. It will degrade, sure, but I need to keep water out of the area. Any other ideas? Just think floor pan, thin metal sheet attached to the floor pan for some OE reason. Rust a the edge of the metal sheet on the floor pan (pictured). Need to seal that gap. or do something. Thanks!
 

JHZR2

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I know, this is unfortunately the case. The car was $3k when I bought it with 72k, now it has nearly 140k. I want to slow the rust to get as much more as I can, maybe another 30-50k out of it, Id imagine is feasible depending upon how much force is on that transmission support. So I want to passivate and slow it as much as possible...
 

JHZR2

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I will. Its not going to look like much, working on this under the car on my back is a messy and difficult job... not to mention the exhaust is in the way.
 
I think your plan will reduce rust progress dramatically. I would add to the list an annual treatment of the area (preferably at the end of summer to allow the product to creep) with rusproofing product like Rust Check or Fluid Film. This will also give you a chance to see how your patchwork is holding up. I would skip the rubber undercoating all together, once sprayed you won't be able to see what's behind it. There is another option though, if you want to use the rubber coating. Spray the rubber coating with Rustcheck or Fluid Film annually. This will keep the rubber coating from drying out and cracking and will not wash out over time as Fluid Film would. My car was originally sprayed with this stuff and my annual treatments with Krown keeps it nice and soft.
 
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I agree with the KrisZ's ideas. When looking at the OP's picture, the contact area that the cross support bolts onto the floor is the real problem area(and probably where the rust started). No matter how well you paint the exposed rust, there are several sq. inches of area where that cross member meets the floor where salt water can weep into and the rust will progress underneath your paint. While your paint method will give better aesthetics, I think that a creeping oil type system might work better. But, you will have to reapply it at least twice annually (spring/fall). Maybe paint and oil would work. Maybe just do the rust converter, then an oil system. The rubberized coating seems like it would allow rust to get behind it, unless you can get a 100% seal. Fluid Film, Rust Check, and Krown are available in aerosol cans.
 
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The Eastwood Rust Converter got not so good reviews on Eastwood's own web site. Basically it never dried. I think their Fast Etch (naval jelly) followed by Rust Encapsulator might be better. I agree with others that you need something to creep between the cross support and the floor. Consider removing the cross support and doing it and the floor area it was bolted to the same way you are doing the exposed area?
 

JHZR2

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That's why I bought the carwell stuff! Oil coating, which I forgot to put down, will be used. Aluminized bondo? Is that any good? Since it won't be able to be 100% definitely painted, need I worry? Doesn't bondo absorb water?
 
Originally Posted By: JHZR2
That's why I bought the carwell stuff! Oil coating, which I forgot to put down, will be used. Aluminized bondo? Is that any good? Since it won't be able to be 100% definitely painted, need I worry? Doesn't bondo absorb water?
Forget bondo, I just saw your carwell stuff, you're good to go, that oil will creep into areas that won't get painted. thumbsup
 
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Since you now have the option of a seeping agent, I agree you would do better with that. I was suggesting the aluminized Bondo as a moisture rejecting gap filler, since you were originally planning to just seal the area with undercoating, which would have little opportunity to be forced deep into the gap. Regular Bondo is quite moisture absorbant. To the best of my knowledge the aluminized version is not.
 

JHZR2

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Not the best pics, but first step was to brush the rust and cover everything with a coating of Eastwood rust converter.
 

JHZR2

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Everything has cured. Those pics were taken over the last week or so and Ive hit it with T40. Only so much time to pull pics from my phone, etc. Will upload the T40 pics later, they are the least important as there isnt much to see. Ill also review the carwell gun on my carwell thread.
 

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Filled the Carwell gun with T-40. The bottle was missing it's oring (they are mailing me one), so I had a bit of an issue getting it primed, and I don't think it sprayed as much/fast as it will. I was using a 4.2 CFM oiled makita compressor. Worked well, and spots where I can see where I sprayed, like the wheelwell show very good creeping.
 

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I guess. I dont like that in the rusty area, I dont have any reinforcement. dont know if I need it, but I'd always like it in theory at least... After I get the oring, I plan on doing some more spraying overall underneath the car.
 
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