Help Me decide 300TD floor pan rust - PeachParts Mercedes-Benz Forum

rjz5400 · #1 01-22-2016, 11:49 AM

My wife wanted to buy this wagon even though it had some indicators of rust. So we got it because it looks GREAT with a unique paint color and drives well with recent repairs and we have driven it for a year with a few long road trips and as a DD for her.

SO I am doing regular maintenance and fixing some leaks and while I have it I decide to investigate the wet floor mats we have noticed on a few rainy drives. I was Expecting windshield seals or hood hinge rot or similar.

Turns out the water is coming UP from the rotten rocker/floorpan seam weld. It is mostly gone. there is a bit of material around the seat mounts left but for the most part it is a 2" rusted out hole from footwell to seat, then another section from behind the seat to the rear bulkhead of the passenger seats.

This is both drivers and passenger sides. I am sure MANY people are familiar with this scenario.

I am hoping for some opinions/inspiration/recomendations

I have a flux core welder and am not terrible at using it.

I have a pop rivet gun and a big bag of aluminum rivets.

I also have the funds available to spend a bit of money on it to get it in safe condition, either on parts, or paying a professional.

The problems I have getting started on fixing the car are many.

How long will any repair I do on my own last?
How much is this car worth "as is" ?
How much do we really want to keep it?
Who the heck does this type of unibody welding and fabrication rust repair?
Who is right about the safety of various methods of repair which range from (suicide, to "can't see it from my house" )?

Any experience or opinions appreciated.

PS I am in eastern NC and can drive the car if need be if there is anywhere in my area <150 miles that could do the work for a reasonable price or to pull clean parts from.

WGA220D · #2 01-22-2016, 02:05 PM

Using flux core for this type of welding ... not the cleanest method. I have replaced entire floors using a MIG welder with shielding gas. Check around at some independent body shops, sometimes they take on a small project like this for 'cash'. Small patches are
straight forward. Using flex grinding discs to clean away the paint, rust, etc. There are several You tube vids on doing this.

Dan Stokes · #3 01-22-2016, 02:14 PM

Here's my bucket of tricks:

If you use plain sheetmetal (readily available) it WILL oil can. Unless you have a bead roller (or access to one) the slickest trick I've found is to go to your local junkyard or PnP depending and remove a van roof. It will yield a large, fairly flat piece of metal with groves in place and a curved edge which sometimes comes in handy. Remember that every time you bend sheetmetal it gets stronger and that is, in fact, how unibody cars work so the ridges in the van roof give you that.

If you have access to a bead roller you can just cut pieces out of sheetmetal and roll beads where you want them.

Cut back to FULLY SOLID metal. A "LITTLE BIT" of remaining rust will drive you crazy and will come back eventually.

1) Beg, borrow, rent, or steal a gas shielded MIG - you'll understand why once you use it. Flux wire really sucks for sheetmetal.

2) Clean the snot out of both the old metal and your patch panel.

3) Prime all the naked metal with weld-thru primer.

4) Drill 3/8 or so holes and plug weld the floor in place - remember, it was plenty strong enough from the factory.

4) Remember that you can plug weld the parts that touch and then hammer the new panel to meet the old one. Don't weld stuff together unless it's a snug fit or you'll introduce an air gap that rust just LOVES.

5) Buy a good professional grade seam sealer and seal the livin' snot out of all your joints - top and bottom. Smooth it with a Bondo spreader or similar and let it dry according to label directions.

6) Prime with epoxy primer (PPG DP series or similar). Again, let it dry according to their directions.

7) Top coat with the rattle can of your choice unless you have access to a spray gun and compressor - then get real paint in the color of your choice.

8) DO NOT skip the top coat part - that's what seals out weather and moisture.

I've done a ton of rust repair dating back to my Michigan days and it's no fun. However, when you bring one back from the dead it's VERY rewarding. Have Fun!

Dan

Zacharias · #4 01-22-2016, 02:21 PM

When assessing this rust you have to keep in mind that in order to ensure you are cutting back to solid metal, you will be cutting at absolute minimum another 1.5 inches back from the rust, 2-2.5 inches would be preferable.

Also if you haven't scraped the area and are just looking at the initial evidence of rust that can be seen immediately, you can count on the rust area being larger than you now think. When I took my w116 in for the floor repair it was showing a 4" hole behind the seat. When I got the car back, at least half of the floor pan had been redone.

The best route in terms of a nice job would be that a competent shop do it. Reason for emphasis is that lots of mainstream shops take on such small rust jobs as semi-annoyances, put little effort into the work and grab some cash. In fact many shops around here won't even door floor rust work anymore, period.

If you have a high school or community college nearby that does auto body shop classes, that could be a way of cutting costs (or you could sign up for the course and DIY with a full shop of equipment and a teacher at your disposal).

If you want to DIY at home, the flux core welder or the rivets are both okay. If you are doing the rivets properly they won't be that much less work than the welder, once you seal up the patch properly and space the rivets closely enough.

dude99 · #5 01-22-2016, 02:53 PM

I too got suckered into buying a cheap flux-core unit.. they are USELESS for body repair. Hunto on craigslist and buy a gas shielded mig. I picked up a DekaStar mig with gas bottle for $170. Worth every penny.

rjz5400 · #6 01-22-2016, 02:59 PM

all good advise, Ill click about for a mig welder. anyone actually done it on this body or are all unibody steel cars the same?

I see that patch panels are available but seems to be of low quality.
I don't care much for looks but solid structure is a must.

Junkman · #7 01-22-2016, 03:12 PM

I thought about doing rust repair on an old Datsun Z floor pan. It would have been a rig job since I don't have the tools and haven't done much welding. I paid a friend of mine who is an old school body man that likes to do this kind of thing ~$150. The car came back with a patch custom bent to match, welded in, painted and with seam sealer in appropriate places. Money well spent. You have to find someone that has done custom fabrication. Newby parts installers won't handle it.

You do all of the required interior removal and reinstall to make it easy. Someone near you is building rods and will consider your floor pan refurb as routine.

Dan Stokes · #8 01-22-2016, 05:20 PM

Quote:

Originally Posted by rjz5400

all good advise, Ill click about for a mig welder. anyone actually done it on this body or are all unibody steel cars the same?

I see that patch panels are available but seems to be of low quality.
I don't care much for looks but solid structure is a must.

While there are, of course, differences in application, the CONCEPTS used in unibody cars are pretty much the same. If patch panels are available they'll save you a ton of time IF they are big enough. I've had situations where by the time you get the bad stuff cut out the patch panel is like JUST BARELY too small - might as well be a foot too small at that point. If they give you lots of extra metal at the edges they will be a great help.

I'm not sure what you mean by "low quality". If you think the metallurgy is lacking you may be right but there's really no way to determine that. If the stamping quality is iffy that still might be the best thing available. Not factory but OK. Most Asian imports these days come with an E-coat and that holds up pretty well though of course it's just a primer and will need to be painted to be durable. Also, it is NOT weld-thru and will need to be removed for your welds - I'd sand it back and prime the weld area with weld-thru primer.

I've tried pop rivets years ago but they just do not make a durable repair. The issue is that every rivet makes a hole in the paint and that leaves a spot for water to get under the rivet from either side and set up a rust situation. Think about the drill bit boring it's way thru the primer on the panel and it's pretty much impossible to reseal that hole. The better you seal it the better the durability but really it's not a good deal.

Notice that I've suggested that you lap weld your panels in place (whether made from a van roof or a commercial patch panel). A purist can argue that the panel should be cut to fit the hole EXACTLY and then butt-welded in place. Technically that would be the highest quality fix but it is NOT easy to do and is overkill for a backyard guy. Lap welds, sealed as I suggested, will do just fine.

EDIT: I forgot to mention that you need to make sure that no water is coming in from above the floor. The windshield seal, sunroof (if so equipped) etc. can all be sources of leaks into the car and it's hard to know if the floor rotted because of leaks from higher up or if the floor metal lost enough paint etc. to allow a rust-out from below. I'll tell you that it's more common for the water to come in from above and end up rusting the floor from the top down. Just check carefully to make your repair last.

Dan

Graham · #9 01-22-2016, 05:59 PM

I had some of the same questions when I started to find rust on my 300D.

Long story documented starting here: Restoration of my 85 300D

I would check for other sources of water ingress. In particular, through the hinge pockets under the hood. The bottom of those rust out and allow water to enter cabin. Then floor and other metal gets rusted out. Unlikely that your car rusted from bottom up.

I won't go into the gory details, but if you look at pictures of my car during restoration, you may get some ideas of where else to look!

Its been a few years now since my car's repairs were completed. I use it as my daily driver. It looks and runs just great. Glad I did not sell when I first found rust. The guys that offered me $1500 should also be glad! But I was very lucky to find Last Chance Auto Restoration in Moscow, Ontario Canada. Owner John did a great job at a great price.

rjz5400 · #10 01-22-2016, 06:05 PM

I believe I have found your thread before and will look again at the whole story.

Perhaps I haven't searched hard enough to find the right man for the job>!?>?>>?

And yes the rust almost certainly started from a leak, what I meant was the WATER in the cab was wicking up through the Massive holes in the floor. I have done well in the past finding and stopping the common hinge pocket rust pockets and sunroof leaks.

and Yes I do need to fix the hole hidden under the battery in this particular car which was likely the cause of all the trouble on the passenger side at least.

Ill try to get the pics uploaded, I have recently updated my computer and it didn't transfer as I thought it did.

Dan Stokes · #11 01-23-2016, 09:00 AM

Hey - I just pieced together who the original poster is! Duh! Sometimes I'm a little slow. You can borrow one of my MIGs if you want. If I wasn't so tied up I'd help but I'm booked for probably a year out right now between the Volvo and the S-10 and racing. I'll ask around and see if I can turn up any one who could do a nice job for you - I know some folks to ask.

Hope you and The Bride are doing well. I was at The Harp the other day and thought of you.

Dan

Air&Road · #12 01-23-2016, 10:09 AM

You REALLY need to use gas. It allows each little weld to be welded over without cleanup. Doing the same thing with flux core or a stick would take forever if you were to clean properly between welds and even then you couldn't do a good job.

My $0.02

MagicBus · #13 01-23-2016, 11:45 AM

I'll be the voice of dissent here. I actually fixed up my 240D with Klokkerholm rust repair panels and yes... a flux core mig unit from Harbor Freight. I swapped out the Harbor Freight flux wire for Hobart flux wire and got much cleaner welds. I've never used a gas-shielded mig, and have no doubt that it's tons better for the job, but this can be done with flux core, especially if you're working on floors, where cosmetics aren't necessarily a priority.

Obviously, I did have to grind the welds, but it really wasn't a deal-breaker for me.

So, I'll say this can be done (I had no experience going into this). Use a gas-shielded mig if you can get your hands on one, but if all you can get your hands on is flux core, don't necessarily be discouraged. Just my $0.02...

Dan Stokes · #14 01-23-2016, 12:19 PM

Both of my MIGs are gas-shielded and he's welcome to use one of them. We're both in Wilmington and he's been to my shop so he knows where it is and I'll say again - come and grab the Lincoln. It has plenty of power for sheet metal (it's a 100 amp). I have a stainless steel spool in it right now but that's an easy change.

Dan

bsmuwk · #15 01-23-2016, 05:12 PM

I have a wagon with perfect floors that I'm chopping up. Take pictures of the spots you want and I'll cut them out for a couple bucks + whatever shipping is.

Getting rid of the car in the next couple days.