82 300CD Rust Repair Help - PeachParts Mercedes-Benz Forum

skeppa12 · #1 03-05-2022, 02:43 PM

Hello,
Always like the W123 chassis Mercedes and have recently picked up an 82 300CD.

While trying to clean/restore the engine bay, I came across some rust, and then some more rust and so on it went. The more I dug, the more I found.

With that said, I am looking for some advice on how to best sort this rust out (pictures attached). Another member has suggested welding, which I would hire someone to do for the battery try holes, but am not sure the best approach for the rest. Try and source a replacement panel from a donor car or fabricate?

Any ideas on a best approach to tackle this rust economically? Anyone have luck with buying from Ebay?

Am in the Hamilton, Ontario area if someone is local and does this type of work.

barry12345 · #2 03-05-2022, 03:56 PM

Have to really have a look at the whole car before deciding anything. Up on a hoist is required.

Hard to say what you may find. Rust hides under the factory undercoat. That looks like a fair amount of work to repair. How far the damage may extend is not known yet. In that one area alone.

Farming out rust work has two issues. Most places do not want to do it anymore. Plus it can be expensive. These cars are great for learning how to do things on. I live on the east coast of Canada. Rust is bad here. Worse than the Ontario area where I am from.

skeppa12 · #3 03-05-2022, 06:39 PM

Self help is the best help....
Will have to start shopping MIG Welders and some lessons looks like.

Being from Canada, have you found a spot anywhere within the country that would supply panels? I know that there is a website raybuck.com which has some but is in the US.

Diesel911 · #4 03-05-2022, 06:58 PM

See post number 12. I go by 300Dman over on benzworld.org.

Note the 2 pics are of the lower right front of the passenger side (US) floorboard. I did the same inside of my trunk on each side.

Note that this is just for patching up a hole not for an area that has is part of structural support. They sell fiberglass cloth and resin for hole filling purposes. I used what I already had.
https://www.benzworld.org/threads/rear-window-rust-repair.1259945/

There is also anti-rust paint/coating like POR-15 that can be used with fiberglass cloth to patch up holes and it dries hard. I have no experience with it. I wondered why the stuff often came in small cans and I found out that exposure to air hardens it. Hence once the lid is opened on a can the time period to open and use it again plunges.

Air issue is somewhat the same with rust restoring paint from autozone. In about 2 weeks after being opened what is left in the bottle starts to cure.

JHZR2 · #5 03-05-2022, 09:14 PM

Some of that rust concerns me, some doesnt. The hole in the front of the rocker, and the hole by the sway bar mount point are the most concerning.

You need to cut to clean metal, and then weld a patch in.

In some circumstances, you can literally glue patch metal to bright metal that you have ground. In many ways this can be a superior repair, I did it on one of my Cummins trucks last year and Ive been happy. Why this is good is because the panel adhesive IS structural. It is OE approved for structural use (assuming you buy the right stuff). It includes corrosion inhibitors and chemically bonds to the bright metal preventing the metal from being able to rust.

Here is how I used that to cover and patch floorboard perforation in my truck. Ive been happy with it.

https://bobistheoilguy.com/forums/threads/minor-floor-rust-repair.340914/page-4

It is another tool in the tool box. Not saying it is for all uses everywhere. It isnt. But in some cases where you cannot get behind a welded panel to properly rustproof, IMO it is superior because the adhesive is the coating, corrosion inhibitor, waterproofing, etc., and you know it will cure. A weld that has bare metal on the back/inside will just rust again...

skeppa12 · #6 03-06-2022, 10:59 AM

Thanks for the links guys.

The sway bar mount itself looks solid but I will take off the rubber bushing and see where I stand. Am a bit worried about finding the right panel for the fender liner to attach to to fill the front of the rocker. Will search the forum to see if anyone has repaired this previously to get an idea of the approach to take.

Patching up the holes also doesn't look like too bad of a job and I do have some experience with POR15.

vwnate1 · #7 03-06-2022, 12:23 PM

Will you be using this thread as an ongoing repair article ? .

You might could buy an average beater 300CD that's mechanically sound and not rusty, use it plus the best parts from both to make a nice build....

JHZR2 · #8 03-06-2022, 12:28 PM

Quote:

Originally Posted by skeppa12

Thanks for the links guys.

The sway bar mount itself looks solid but I will take off the rubber bushing and see where I stand. Am a bit worried about finding the right panel for the fender liner to attach to to fill the front of the rocker. Will search the forum to see if anyone has repaired this previously to get an idea of the approach to take.

Patching up the holes also doesn't look like too bad of a job and I do have some experience with POR15.

If you go with structural adhesive, you can form patches with 22ga (or thicker) steel, including galvanized (which you can’t weld because of toxic fumes, as I understand it).

Just template with cardboard or paper, use an angle grinder to cut the steel, then brakes and hammers.

t walgamuth · #9 03-06-2022, 01:20 PM

The four door cars have drains in the bottom of the doors to expel water which gets inside the door. On a coupe I am not sure how it is supposed to get out but fact is it does not work very well. There may be a drain tube in there somewhere which needs attention from time to time.

JHZR2 · #10 03-06-2022, 01:22 PM

Quote:

Originally Posted by t walgamuth

The four door cars have drains in the bottom of the doors to expel water which gets inside the door. On a coupe I am not sure how it is supposed to get out but fact is it does not work very well. There may be a drain tube in there somewhere which needs attention from time to time.

Pretty sure my coupe has drains like any other door. I’ll have to look.

In these old cars it’s worth opening up the doors, lubing stuff, and getting a coating of woolwax/fluid film in there.

skeppa12 · #11 03-06-2022, 02:14 PM

Quote:

Originally Posted by vwnate1

Will you be using this thread as an ongoing repair article ? .

You might could buy an average beater 300CD that's mechanically sound and not rusty, use it plus the best parts from both to make a nice build....

I will update the thread with my progress on this work and I hope it will help someone in the future.

I am tracking my progress with the build through TikTok (although I know this may not be popular here) and a link to a video about this rust (the beginning of it) is here:

https://www.tiktok.com/@prodani12garage/video/7071677710027787525?_d=secCgwIARCbDRjEFSACKAESPgo8MhNOAkW9Z9ky3ZovbRS8FeQzU9n%2FPPMX4k4UBWt5DjHiVxBH GOQKiVeHblAChIj2HccgNtFTWTaTKrz%2BGgA%3D&checksum=401b23acf64cb630aa015a7214b1fdd9910f00dc5ab2e5e9eabc27ed02dc086d&language=en&preview_pb=0&sec_user_id=MS4wLjABAAAAU78lxm-hlmEkc0Ak7gl7_pljAp2kFIhzuF88nh-WihRnrKWWt2Q3B6imWtoeE-SH&share_app_id=1233&share_item_id=7071677710027787525&share_link_id=9B565AF4-178C-4E8F-A351-850110CFB92C&social_sharing=v2&source=h5_m&timestamp=1646593750&tt_from=copy&u_code=dle92bl5ic8mhb&user_id=7026396529545217030&utm_campaign=client_share&utm_medium=ios&utm_source=copy&_r=1

I rebuilt the turbo, checked the starter and alternator are working and have ordered suspension components for a suspension refresh. My thoughts were to build this thing to its full glory but am stuck with the rust repair work

skeppa12 · #12 03-06-2022, 02:16 PM

Quote:

Originally Posted by JHZR2

If you go with structural adhesive, you can form patches with 22ga (or thicker) steel, including galvanized (which you can’t weld because of toxic fumes, as I understand it).

Just template with cardboard or paper, use an angle grinder to cut the steel, then brakes and hammers.

A local used car shop suggested this approach as it was much less labor intensive and effective for the panels hidden away from view. I'll have to source some steel and start fabricating patches, whether I choose to weld or use structural adhesive, will still need the steel and a rough idea of the patches to make. Ideally I would purchase premade patches and have them welded.

The W123s in good structural condition are very hard to find here north of the border and with the price of used cars, am not sure it would be economical to get a donor car. Its worth a look

skeppa12 · #13 03-06-2022, 02:25 PM

Quote:

Originally Posted by JHZR2

Pretty sure my coupe has drains like any other door. I’ll have to look.

In these old cars it’s worth opening up the doors, lubing stuff, and getting a coating of woolwax/fluid film in there.

That's very true. It is on my to do list (which keeps growing)

BillGrissom · #14 03-06-2022, 04:20 PM

Coated steel, including galvanized, welds better for me with my cheap non-gas Harbor F flux-wire welded. Probably because the nickel or zinc outgas to act as a shield (melts ~800 F). Try not to breath the fumes, though I don't think they are terrible like heavy metals, and indeed are in vitamins, but many welders say they get a headache after breathing zinc fumes. You would mostly be doing a bunch of tack-welds on sheet metal, to avoid burn-thru and warpage, so just hold your breath when tacking. Need to spray the backside before welding w/ "weld-thru primer". I just use Rustoleum High-zinc galvanized spray paint from Ace, and again after welding, grinding, and cleaning. I agree that using structural adhesive or even fiberglass matt can work. Those areas are of minimal concern re body structure. The lower rust is typical when leaf debris which got past the cowl vents collects. Water is supposed to drain out at the bulges in the plastic mud shields, but when I've taken them off my cars, that area was clogged with leaf gunk.

The corroded battery tray is typical. Can't buy a new tray affordably. I fixed one by welding on a 1/3 section of bent galvanized steel, but then got one from another car before using it. Didn't rust thru the firewall in my 2 300D's, but I caught it starting in the 1985 when there was a big nasty blob of white powder behind the battery on the firewall (zinc-oxide?). Chemistry can be evil.

vwnate1 · #15 03-06-2022, 09:09 PM

Please don't like to other sites that are prime tracking places .

I agree, do the mechanicals first, as I don't weld I'm interested to learn what you do .