I recently purchased a '84 300D that I thought was mostly rust free. I've been poking around (quite literally) and noticed that the right front jack point is rotted through several inches around the jack tube. I also found a small rust through point below the battery tray.

I've heard that Miracle Paint and fiberglass cloth can be used to patch rust through points. Is it possible to repair the rocker area around the jack tube with these materials? I know these are common rust point on W123s so what have others done with similar rust issues?

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1989 300CE

For the rusted rocker jacking point I ground away the rusted area and surrounding area of the heavy under body coating then using pop rivets with the heads in a recess made by drilling a shallow dimple using a reground 5/16" drill. This hides the rivet head in the patch material. I used a fairly heavy pice of galvinized metal. Then a light grind to feather the patch and spray with a black under body coating, two coats and the patch is gone. Don't use as a jack point any more. The rivits are on 3/4" spacing. Aluminum body rivets 1/8" stem with steel pull pins.
By this time you are good with tin and rivets and can repair the battery area rust the same way. The underbody material can be painted after it is real dry.
I use a shaker can product called European Texture Rubberized Gravlguard from NAPA. It looks exactly like the factory coating

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1984 300SD turbo 126
"My true love"

God made me an atheist and who am I to question His wisdom

I know many will disagree, but I see no issue using fiberglass and filler for sheet-metal repairs, like behind the battery. Even if you could weld, you might not have access to the backside, which would then later start rusting (weld-thru primer helps). You could also catch the car on fire. Cut back to sound metal, prime well, then fiberglass (woven matt works best). I like Rust Destroyer (converts rust, etches bare metal). Many promote POR-15 ($$$). If totally shiny metal, a self-etching primer might be best. Car shows put Bondo or fiberglass direct on bare metal, but I think primer first is better.

The rocker panels are structural in my opinion on these cars. Something to keep in mind.

I would weld or get someone to weld in strong patches and do a little fill work using mar glass or short hair fiberglass. Then drill holes on the backside of the rocker panel and spray oil in there mixed with a little grease. This heated by placing a container of it in boiling or pretty hot water to thin it first. I use an electric single burner old hot plate.

For all practical purposes the rust will stop or at least slow to an almost neglishable rate from that point forward. You have to make sure you spray oil into all the cavities.

I think I remember there is a bulkhead pretty far forward on the rockers on these cars. So you have to make sure you spray your mix inside on both sides of it. Using almost anything else inside the rocker panels will probably speed up the natural rusting process.

I grew up using Bondo straight to bare ...and roughed up ... metal...it is a physical bond...not chemical ..
but it seems that since the introduction of EPOXY PRIMER... there is latitude in the decision..

Can bondo be applied directly to bare metal - Hot Rod Forum : Hotrodders Bulletin Board

Those guys are so young they are even asking it the other way... they had not heard of bare metal to Bondo .... LOL

On any of these products or suggestions... READ THE INSTRUCTIONS from Both of the manufacturers .... for instance... if you need to use a metal etch... like Metal Prep.... you need to rinse it well ....and dry it and immediately apply the next process.... just like you would with sand blasting... where it is totally exposed to moisture in the air...which you can SEE oxidizing within MINUTES...
I do not like the idea of weld through primer... clean your metal and weld it right then... properly prepped.... I do not want any burned residue caught inside my welding. Simpler is better. Learn the basics and follow them for good long lasting results.
I favor fiberglass Woven Cloth instead of mat.... bends into corners and is stronger per unit of thickness and weight... but that is ONLY if one has already decided on fiberglass..... its major problem is if you have to go back in later... WHAT A MESS....
Whereas for instance... rivets with a small amount of silicone sealer is pretty nice to remove...

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

I am ordering some Miracle Paint this week and will let you know.

I have a half of battery tray that I would like to make complete, but the big issue is a big hole right by the corner of the rear window. I want to make my trunk watertight, and stop the rust

I think that I can brush some of the Miracle paint onto the backside accessed through the trunk. Now that I'm writing this that seems doubtful for the backside of the quarter panel

I am wondering about some spray on rust converter to use from the underside. I don't know which way to go, but for the outside it is definitely the Miracle Paint.

I don't know whether to get from this place on the net that sells a kit, or get it from this other guy for less money and get the stuff made for painted body parts. I guess I just answered my own question.

If by miracle paint you are referring to POR15..
be sure to read the instructions before you invest...
the prep and the conditions needed for it to work correctly are different from normal paint...
If you use a ' rust converter'... you need to coat that with something waterproof afterwards... some rust converters need to be brushed before applying paint.. get any loose stuff off....
if you are just trying to stop rust in a space not easily accessible... then try ' Fluid Film'...
farmers use that for those kinds of places on equipment... available from New Holland tractor dealers and other places...

__________________
1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

Assuming the goal is to make the car durable and safe, you MUST weld in metal in the rocker area as it is definitely structural. I've done a lot of body work over the past 50+ years and fiberglass and paint WILL NOT fix this kind of damage, just make it look OK. I can't tell you how many of those patches I've cut out and replaced with metal patches that I've bought or fabricated after they've cracked away from the body structure. The body will flex even more with an improper repair and it WILL pop out a bonded repair, including one held in with rivets.

Now, there are structural bonding agents that can work but they must be used with VERY CLEAN metal and they're painfully expensive. I have the Lord Fusor system with was (at the time I bought my applicator) about the cheapest one out there and it was still pricey. This is the repair system used for body panels that are fused from the factory, as many are now starting to be - but this is not an easy short-cut for proper repairs.

You can use the fiberglass & paint process in non-structural areas with success. For example, I once did a Trans Am that had bullet holes in the sail panel as the result of police gunfire (it was used in a robbery). That section of the top has limited structural stress and I didn't want to replace the headliner so I did the glass and it held up just fine.

POR-15 and those types of products work fine if used as directed and if you're after a finish (not structure) on a part that was rusted. That application is really what they're made for.

Dan

I suggest doing what you need to to stop the rust...
and FILL IN THE JACKING HOLE...so it can not be used...
it is most certainly a structural member...
and you have to go all the way to good metal to start the fix...and really know how to do that... which is hard to do correctly....
there are places under the car to properly jack it up.....

__________________
1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

Having been through this a couple of times:

- The rocker panel surround doesn't affect the use of the jacking point. The jacking point is part of a structural bracket that connects to the door pillar.
Another pic here.
- The rocker panels are structural and it would be best to weld in a patch. It is not a big job for a shop. Cost me C$182. Before and after pics here.

- Re spraying in after the weld, you can do that through the removable plug holes along the bottom of the rocker. I have used Fluid Film as well as the canned RustCheck and Krown products we can buy in Canada. But I am about to take my car in for it's complete annual rust treatment where all cavities, underbody etc are treated.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Make sure to get all the rocker panel cavity. Just feed a feeler wire in the hole and remove it for comparison on the outside of the rocker.

Again I believe but cannot remember for sure. There is a bulkhead in the rocker way up towards the front of it I thought. Before the jack point though. Undercoating is one of those things to do properly you have to do it yourself unless you stumble upon a really ethical person to do it.

Not sure on this body but many inner rockers can be accessed by removing the sill plate molding and drilling an access hole thru and into the rocker box cavity. Anyone tried this? It's how we undercoated the rockers on Buicks back in my dealership days but I haven't done a M-B.

Dan

Based on what everyone has said, I will cut out the affected rusted rocker panel and get a shop to weld in new rocker panels. What should the back of the rockers be treated with so they do not rust out again? I suppose the weld points would be the most vulnerable for corrosion. I'm going to patch the battery tray area with the fiberglass cloth and treat everything with rust inhibitor.

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1989 300CE

Our rust treatment shops up here drill holes along top of rockers and spray through those. I used the ones underneath. They drill in many places such as door pillar. But they miss key areas for W123 like behind/below battery, cavity behind front wheel wels etc etc.

I would like to do a proper job myself, but need a gun, high capacity compressor and a barrel of Rust Treatment. NAPA sell all of these up here, but you have to put out beaucoup bucks. I pay about $110pa at Krown. Canadian Tire, believe it or not, do it too and use a well thought of product.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Hmmm - You are in Canada? Use Fluid Film from Princess Auto or TSC. Or Krown in a rattle can. Or Rustcheck in Rattle can. At those companies, or at CT.
Better still go get your car rust sprayed.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5