Floor pan rust repair pics, or why to replace your A/C evap drain
 

So I noticed about a year ago that I had a rust problem in the driver's side footwell of my 1984 300SD, when I pulled up my carpet and found this:

http://lh5.ggpht.com/_UHcRRxr-wEo/Sx...1%20before.JPG

Needless to say, I did not want to let that stand. Unfortunately it took me a while to get around to it, but it didn't end up being as bad as I thought it would. In the meantime the attachment point to my accelerator pedal rusted through, but I doubt I would have been able to save that even if I'd fixed it immediately. For the last month or so i've been rolling just pressing the bar that the accelerator pedal used to attach to, I'll fix that at some point.


Anyhow, this was my strategy for fixing this-

1) Remove the pavement insulation/noise dampener that's currently in the footwell using a heat gun

2) Grind away the rust with my rotary tool (use Proxxon, not Dremel!)

3) Use some POR metal ready (I think this stuff is just phosphoric acid)

4) Paint it with POR-15

5) put down some new butyl rubber based sound dampener instead of pavement (from second skin audio, they call it 'damplifier' :rolleyes:)

6) peace of mind!


It worked pretty well, and the rust wasn't nearly as bad as I had feared! I'm actually posting this while I'm waiting for the POR-15 to dry, by 10:30pm it will have been 4 hours, then I'm going to put on the butyl rubber.

Here are the pics!!

Here's after I pulled up as much pavement as I could with my hands, without using the heat gun-
http://lh5.ggpht.com/_UHcRRxr-wEo/Sx...4/IMG_0963.jpg

Now putting up some foil so I don't inadvertently melt the pavement I don't want to mess with...
http://lh3.ggpht.com/_UHcRRxr-wEo/Sx...20pavement.JPG

After most of it has been removed. Initially the pavement is composed of pieces the size of little pebbles. Using the heat gun melts them together into something that pulls off much more easily.
It stinks though, if I had to do it again though, I'd wear a mask while doing this part. I blew my nose after I was done, and it was pitch black!!! I bet it's like I just smoked two packs of cigarettes...
http://lh5.ggpht.com/_UHcRRxr-wEo/Sx...20pavement.JPG

Ready to start grinding...
http://lh5.ggpht.com/_UHcRRxr-wEo/Sx...4/IMG_0971.jpg

Partially done, my fantastic Proxxon rotary tool in the foreground. WAY tougher than dremel, it has a regulated motor (maintains speed under load), and uses a steel collet w/ chuck key.
http://lh6.ggpht.com/_UHcRRxr-wEo/Sx...4/IMG_0974.jpg

Ready for painting. In the end, the rust was much less severe than I had anticipated. There's a divot in the floor pan, and before I had removed the asphalt I had thought it might have been a partially developed rust hole. Nothing but some surface rust, I was happy to be wrong!
http://lh6.ggpht.com/_UHcRRxr-wEo/Sx...4/IMG_0979.jpg

Painted!!! Now I'm going to go back outside and see if it's dry...
http://lh4.ggpht.com/_UHcRRxr-wEo/Sx...4/IMG_0986.jpg


I'm reasonably certain the A/C evaporator drain was the source of the water that caused this, as the one in there was totally useless. I've replaced it, and I strongly recommend that W126 owners at least have a look at theirs. It's pretty easy to check, you just need to pull the carpeted panel on the left away from the center console and it's right there.

Finished! Ended up using two layers of the butyl rubber stuff to match the thickness of the existing pavement insulation that I didn't cut away. Now I just need to fix the attachment point so I have a pedal...


http://lh4.ggpht.com/_UHcRRxr-wEo/Sx...4/IMG_0987.jpg

http://lh6.ggpht.com/_UHcRRxr-wEo/Sx...4/IMG_0992.jpg

http://lh6.ggpht.com/_UHcRRxr-wEo/Sx...4/IMG_0994.jpg

Curious, I assume that vacuum lines and wires run under that quarter circle plastic track/cover on the floorboard. How did you remove all that for this repair? Is is only vacuum lines and you were able to disconnect it all? Or is it only wiring to the driver's seat?

My only concern is if the butyl stuff is in intimate contact with all the valleys in the floor metal, otherwise it may not deaden sound/vibrations transiting through the metal, and may also allow water/moisture to be trapped under there.

Those are actually air vents that connect directly to the HVAC unit behind the center console. They blow on the feet of the rear passenger, there's one on the passenger side also. They were quite easy to remove, each is held in place by a single phillips head screw.

I'm not sure precisely *when* they're activated though. I suspect that air comes out of them whenever air is being blown on the feet of the driver and passenger.

You're absolutely correct- there are places where the butyl stuff is not in contact with the floor due to the metal not being flat.

However, I'm not too concerned about it, as that was the case with the original insulation as well. When I pulled it up it was very clear that it had not been making full contact, and in some cases I could put my finger between the pavement and metal.

Then again, the reason we're talking about this is because it was rusting, so going by how it was before may not be the best approach ;). That said, the only time I hear about people having problems is when the water load is relatively large, due to a windshield leak or wasted A/C evaporator drain tube, so I think i'll be OK going with how it was to start with.


As you say, there's also the issue of whether or not having air pockets is better or worse for sound dampening. It's not obvious to me which is better- having the rubber in contact might better dampen vibrations in the metal, but having air pockets might be more effective at preventing sound from being heard in the cabin. Regardless, I've heard that pound for pound this rubber stuff is more effective, so beyond using it instead of pavement I didn't worry about it too much.

Looks like you did a good job. My W124 has a similar set up and I plan to replace the condensate hose early Spring 2010. No leaks yet but might as well be proactive.

Thanks for the write up. This gives me the confidence to do mine. Last winter I noticed some moisture in my carpet and I suspect I have a hole somewhere down there. I haven't pull up the barrier to check but I did notice a crack in it where my heel pressing the accelerator rests.

Once I get my suburban back up and running I'm going to tackle this issue on my SD.

Where did you get your POR from? All you need is the metal ready and the sealant stuff, correct?

My car had a water leak below the windshield, and the tar material looks just like you're "before" picture. This gives me a lot of hope!!!

-Jason

Good luck, if you still have the attachment point for the accelerator pedal on the floor you're in better shape than me. Also, notice on my 'before' picture that the cracks in the insulation extend much further than the actual rust, so cracks may not necessarily mean you have rust damage.

There's a substantial divot in the floor pan quite close to where your heel tends to rest, and mercedes does leave an air pocket in there. Time and weight alone might cause the cracking as the pavement is pushed into the divot.


I bought the POR directly from them at www.por15.com , and all that I purchased from them was metal ready and the POR-15 paint. I suspect the metal ready stuff is just diluted phosphoric acid, there's a decent chance I was a victim of their marketing and I could have found it cheaper elsewhere. But it was convenient, so hey, I'm fine with it.

I'm not sure if there is any rust...but there most likely is since there is moisture that is creeping in when it rains or snows. If I recall, it looks good from the underside. So I may just be in for metal repair and then putting the metal ready and sealant on. I do have a welder if I need to do anything more...hopefully I don't. But if there is a hole or crack in the metal I will seal it up first with the welder.

So you are saying there was no hole in the floor pan in yours, just rust on top?



I found a kit for $20 online (quart size). I may see what the local Farm Supply/Auto Parts stores have in stock before I order. It may take me awhile to get around to it as I want to be able to park it for a few days to do the r and r and I need to finish the IP install in my suburban in order to do that.

Thanks again.

attached pictures
 

attached pictures, and moved to body forum.

an alternative to the method above to get off the crap is to use a metal wire cup brush. you can attach it to a drill and make quick work out of removing the big pieces. remember too that if you want to apply por-15 or the like, there needs to be rust for the por-15 to adhere to.

also behind the firewell wall right behind the pedals is a layer of black foam that is *highly* flammable. when i was repairing/welding my 87, i read on one of the posts to be careful of this. i pulled out a little piece and boy whoever wrote this was right. so if you are going to use any type of flame source to remove the crap, DON'T. you've been warned!

Rust isn't good for any coating, including POR-15. It is just that it can tolerate some rust and still work (I would still remove all the rust). I pretty much know what the stuff is from the MSDS, and there isn't anything to make me believe that rust would improve it's adhesion.

Rust is an unstable surface.