Rust question on Rear subframe mount

[freeheelboy]

Hello everyone.

I just inherited a 1974 BMW 2002 with good structural bones but some serious floorpan rust issues. I have a decent background restoring airheads but autos are a new venture for me. I figured I would start with the best...

These are pictures of the interior rear compartment under the rear seat. It is the top portion of the rear subframe mount.

The mount itself feels solid still and most of the structural elements inside have surface rust (no carbon flakes that I can see)

I plan on grinding as much rust off as I can reach and squirting POR15 "Metal Ready" on all the interior areas to neutralize the rust I cannot reach with grinder. Then I plan on re-welding 16ga. plate over the top of the mount to seal the interior from road debris and strengthen the mounting area.

My questions:

1. What is this mount supposed to look like in stock form from the interior? As you can see from the picture the sheet metal has rotted completely away from the mount area. is there supposed to be a hole for access to the top of the mount?

2. Any additional suggestions on processes or materials for this repair?

3. It looks like the interior sheet metal simply rests on top of the subframe mount and the structural element is under the floorpan. How do I check to make sure this subframe mount is structurally safe?

Thank you for looking and I look forward to your help on this issue.

Cheers,

[Tommy]

Congratulations regarding your new 02 and welcome!

Look at my project blog to see the structure of that area. Most of my rust problems were on the underside so I don't even have a picture of the inside. I'm sure someone can provide a pic of inside, but yes the hole is supposed to be there. Anyway you should check the structure from below.

http://www.bmw2002faq.com/component/option,com_forum/Itemid,50/page,viewtopic/t,309762/postdays,0/postorder,asc/topic_view,/start,0/

Once more welcome, and please post some more pics of your car.

Tommy

[TobyB]

Ug. There's a reinforcing plate that spreads the load from the point

(bolt) to the sheet metal. It's welded aroudn the perimeter.

It's also welded to the inner rocker- check it there carefully,

and check it's structure to make sure it's not swiss cheeze.

And before you spend any real time fixing it, make sure the other

common rust spots (rear spring perched, inner rockers, rear fender lip,

front inner fender lower lip, front a- pillars, nose lip, etc)

aren't all rusted through, too. It's not all that common, but a real

roach won't be worth fixing, just driving. Usually there are a

few problem spots, and then you get a good car- unless you're in the

rust belt...

search '3m rust fighter' or 'body cavity wax' for a good discussion or 4 about

how to protect this structure once you've fixed it.

Good luck!

t

[FB73tii]

Below are a few pics from my previous car. In addition to the floor pan rust above the rear subframe pads I had inner rocker rust, so needed some reconstructive surgery to fix. Best of luck on the "rust-o-ration." --Fred