Found Rust, Not Certain How to Fix

[CRatcliff]

Hey all,

Found some rust that seems to go not all the way through, but I can't fully tell. When I first saw it it looked like it was coming up from the bottom, but when I stripped off the undercoating the rust seemed minimal and cleaned up easily. Images of the rust are [here]. One thing I'm noticing is that it SEEMS like there might be a mismatched shape (it drops down on the underside, while in the interior the shape continues to the edge. But the rust doesn't seem to go into the mismatched area.

I'm just trying to figure out what my next steps are - just grind out the rust from the inside until there is no more rust (plus 4" outside of the rust to verify it is fully caught?) and then see where it goes? I've never had to cut a panel out before, and don't even know where to start.

Thanks all!

 

[OVERDRIVE]

If you don't want to do any welding, wire wheel on a grinder and POR-15? That's what I've usually done.

 

[CRatcliff]

If you don't want to do any welding, wire wheel on a grinder and POR-15? That's what I've usually done.

Awesome. Okay thank you so much. The fact that some of the rust was UNDER the metal (you can see the flap of it pulled up) makes things tough, but I think I'll just have to cut that flap out and clean it and maybe fill with bondo or epoxy or if it's deep enough we just cut and patch.

I only have a crappy mig welder, so I'd worry about the quality of my patch job, but maybe I can hire a welder to pop by.

 

[CRatcliff]

Bumping this!

 

[tbrcktch]

Looks like this is the drivers side rear passenger floor section. Have you pulled the carpet up to look for rust/corrosion? If it's rusted out on the inside, you should also pull the drivers side front carpet up to check for corrosion there as well. It is not uncommon for firewall water leaks, to leak enough water down the firewall, to the floor, sometimes, all the way back to the rear floor section, and rust it out, as well as the front section. The cause is frequently firewall grommets that are split/torn/missing/or not fully installed properly. Could be vacuum hose or wiring grommets. Also a possibility of a windshield seal leakage. The water leaks down, and pools up, and can take a very long time to evaporate (the carpet keeps air off the water, so it can't evaporate), and if you have a large/frequent leakage, it could stay wet for a very long time. Good luck, hope you don't find any corrosion on the inside.

 

[lookforjoe]

Better pics? Coating with POR15 is only OK if there is zero flex in the panels, so typically frame rails etc., rather than floor pans. Since it forms a shell, any flex in the panels will crack the coating & then you're fucked.

 

[CRatcliff]

Hey yes sorry! Images were in the link in the first one ('cause I couldn't figure out how to make them small / there were so many). Attached here now!

 

[lookforjoe]

I'd cut off the piece that you have hinged, then go at the area with a flap disc (angle) grinder, to evaluate the spread. It looks like it travels further the right in your pic. To do it right (keep it original), you would probably need to cut out the sheet metal & recreate the overlap seam. The rot is likely deeper than it appears, it usually is. Since you say you don't have a decent welder, it's really a question of whether you will be happy with a DIY cleanup as best possible, or making repair panels (pretty simple here) & then having someone else do the actual weld...

 

[2manyturbos]

That really isn't that bad. If you have adequate compressed air, get a 3M clean and strip wheel, an arbor to run it on and use an electric drill or die grinder to clean up the rust. don't go more than 1/2" past the rust in any direction. Treat the area with phosphoric acid to convert the rust and then coat it with an epoxy primer and paint. apply seam sealer over all that. Spray rubberized undercoat over the area when done. The main thing to do is fix the source of the water getting into the rear floor. 99% of the time it is a windshield leak. The water runs down the channel next to to rocker all the way to the low spot in the body which is where your rust is located.

 

[mitch1971]

Nice work cleaning it up. Now it’s got the seats and carpets out and cleaned up it’s a nice easy job for a welder to cut it out and weld in new metal. That won’t cost much to weld but make sure they cut it out not patch over the top.

 

[CRatcliff]

Awesome, thanks all. I'll cut the flap off and then grind out all the rust and see how far / deep it goes, then I'll post some pics!

 

[2manyturbos]

This is what I'm referring to. These are aggressive. It will peel that seam sealer right off and send sparks flying everywhere. Make sure you use a face shield if you use one of these wheels.

https://www.mscdirect.com/browse/tnpla/01608561?cid=ppc-google-Smart+Shopping+-+MMR++Abrasives+NCA&mkwid=%7cdc&pcrid=592524881260&rd=k&product_id=01608561&gclid=CjwKCAiAleOeBhBdEiwAfgmXf-ZlqXkeQyXh6gTNhsvHO96qyJ0xM64ZnYjHBML5Ew7NoU8QaL69ABoChSUQAvD_BwE&gclsrc=aw.ds

 

[CRatcliff]

Ooooh alright. I've got the wire wheel on the grinder and might even hit it with the flap disc for a minute.

Also I'm pretty sure the leaks I found were actually at the tops of the seams of the firewall. Already cleaned and re-sealed them, but I'm realizing I may have wanted to hit it with some rust-converting primer or something first.

 

[hiperfauto]

There is a torsion box welded to the floor pan in that area. That explains the mismatched shape between the top and bottom. That also means there is a dead air space under there that may have been compromised as that rust looks like its coming from underneath the floor to me.

The torsion box is still available.

The floor pan for a 240 should be very close to a 140, especially in that area since they use the same torsion box -'78.

https://raybuck.com/product/1975-93-volvo-240-rear-floor-pan-driver-side/

 

[CRatcliff]

There is a torsion box welded to the floor pan in that area. That explains the mismatched shape between the top and bottom. That also means there is a dead air space under there that may have been compromised as that rust looks like its coming from underneath the floor to me.

The torsion box is still available.


The floor pan for a 240 should be very close to a 140, especially in that area since they use the same torsion box -'78.

https://raybuck.com/product/1975-93-volvo-240-rear-floor-pan-driver-side/

Ahhh yep this is the information I was lookin for but also what I was hoping was not the case.

I'm going to grind it out and see how deep it goes, but that would make sense as to where that's coming from.

https://www.skandix.de/en/spare-par...v1Xg0U9i-j-HCEPm9tntwi-6SgQXDs_ElipshVi4mpKYk More spare panels.

To replace the torsion box I'm guessing I'm going to need to replace the floor panel and also take off all the stuff mounted to the torsion box? (rear axle?)

 

[hiperfauto]

Hopefully you won't need to replace the torsion box. If it does need to be replaced, you should only need to remove the trailing arm.

 

[CRatcliff]

Hopefully you won't need to replace the torsion box. If it does need to be replaced, you should only need to remove the trailing arm.

Amazing, thank you thank you!

 

[lookforjoe]

This is in someways similar to the situation with my X1/9 - rust on the inside where the floor meets a torsion box on the outside - mine has obvious perforation (area under pedals)

After removing the first layer, there was more to go, ending up with this. Each layer had to be reconstructed in sequence to maintain integrity

 

[CRatcliff]

Oooh yeah okay. I'm really hoping I get away without needing to replace that whole section, but time will tell. Doing the grinding today!

 

[CRatcliff]

Hey all,

Sadly it looks like it did indeed rust into the torsion box. I'm going to order that one right now.

Would the next steps be to remove the trailing arm, cut out the whole old torsion box, and see where the rust is at that point?