underbody rust
 

found some underbody rust around my subframe support bracket on my w115. what else do these bolts go through besides floor pans? Attachment 130554

The title of your JPG says it all.:D

The bolts don't go through anything else. They rely on the integrity of the floor pan to maintain proper suspension alignment.

Time for new floor pans at a minimum.
Check around for other key rusted areas (jack points, trunk deck, front frame rails, inner fender wells, etc.). You might be frightened at what you find. Remember, these are "Uni-body" construction vehicles and rely on chassis components to provide strength.

http://www.peachparts.com/shopforum/body-repair/339888-w114-rocker-panel-repair.html

http://www.peachparts.com/shopforum/body-repair/232688-rear-fenderwell-rust.html

http://www.peachparts.com/shopforum/vintage-mercedes/229683-leg-bones-connected-knee-bone.html

http://www.peachparts.com/shopforum/vintage-mercedes/205060-kiss-death-all-old-mercedes.html

http://www.peachparts.com/shopforum/vintage-mercedes/183947-rust-never-sleeps.html

Just goes into the floor pan - but the whole pan needs to be stiff and rust free which is often a bit difficult for an old Mercedes!

Hah! Well done Mike - super fast posting!

Yeah, I'm bored and have nothing better to do today than surf the 'net.

Drew up a crank trigger wheel for the M115 TBI conversion and am sending the drawing off to have a custom one made. Gonna be a couple of days before it's done so, for the moment, the wife's Benz is sitting in my work area blocking any projects I had planned.

Okay cool i was planning on replacing soon going to tack in new ones and just cut out and most likely fiber glass the rust on the underbody

Bear in mind the stiffeners were put there for a reason when you're smearing fibre glass where once there was metal. If the floor pan is not stiff enough the subframe mounts at the front will probably end up bending at the higher part in the chassis that is in a closed box section which makes it very awkward to repair...

I meant putting fibre glass on the non structural part of the car like the very bottom of the car under floorpans

The entire floor pan is structural. Using fiberglass to repair pin holes is fine. You should not replace an entire section with fiberglass mesh.

If you are unable to get metal clean enough to weld but the metal is otherwise strong. On various cars I've used 1/4" bolts to distribute loads and welded where I could.

An example would be a domestic ( USA ) car with a pinch welded lower rocker panel. Weld the top, bolt through the pinch weld.