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  #1  
Old 10-09-2011, 10:46 AM
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Replacing W115 Rocker Panels: Spot Weld or Adhesive?

My 240 is in the body shop getting the usual rust tended to and some fresh paint. I'm quite sure that most of the rusting was the result of some idiots creating their own jack points.

The bulk of the work, then, is replacing the rocker panels.

I'm torn between two schools of thought about how they should be installed.

1. Use the tried and true spot weld method.
2. Go with a no-weld adhesive.

The body guy is leaning towards adhesive because he's confident that it's the least likely to rust in the future. His rationale is that even welding grade primer melts off during the weld and won't prevent weld seam rust. Also, once weld in place, it's nearly impossible to coat the entire inside of the panel.

He also pointed out that he had one heck of a time getting the front fenders removed. If the adhesive holds up half as well the glue holding the fenders in place, then the no-weld approach should be plenty stout enough to lasts for however many decades the car has ahead of it.

I do like welding because it's a known quantity and I've no first hand experience with the glue 'n go method. But given that even airplanes are assembled with epoxies these days, I'm willing to let him save me some money in labor and use the goo.

Anyone have any experience or recommendations either way?
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  #2  
Old 10-09-2011, 11:39 AM
DeliveryValve's Avatar
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I've used this stuff to bond quarter panels. 3M 8115 adhesive with good results with minimal spot welding while wet. The glue is very tough once cured. I think it would be a good solution to your rocker panel.


Here is some interesting threads about Glue vs Welding all by the same poster.

Welding or Bolting vs gluing panels on, a science project

Follow up peel test on Welds vs Glue.

Real world test on panel adhesives.



.
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Last edited by DeliveryValve; 10-09-2011 at 11:49 AM.
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  #3  
Old 10-09-2011, 02:17 PM
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Quote:
Originally Posted by bipolardave View Post
...
The body guy is leaning towards adhesive because he's confident that it's the least likely to rust in the future. His rationale is that even welding grade primer melts off during the weld and won't prevent weld seam rust. Also, once weld in place, it's nearly impossible to coat the entire inside of the panel.

He also pointed out that he had one heck of a time getting the front fenders removed. If the adhesive holds up half as well the glue holding the fenders in place, then the no-weld approach should be plenty stout enough to lasts for however many decades the car has ahead of it.

I do like welding because it's a known quantity and I've no first hand experience with the glue 'n go method. But given that even airplanes are assembled with epoxies these days, I'm willing to let him save me some money in labor and use the goo.

Anyone have any experience or recommendations either way?
I understand your concerns about treating the inside of the panels - I'm worried about that too. I was planning to treat with Dinitrol (Rust prevention | Rust treatment | Rust proofing from Dinitrol UK supplier). Their cavity spray was described on this forum as being the next best thing to leaving the car in the Sahara (sorry to who ever said that - I remember your comment but not your user name). It is a very popular solution here in rusty parts of Europe.

My worry about gluing on top of paint - if that is part of the plan? - would be that the strength of the bond is then compromised by the strength of the paint sticking to the metal...

I think a well kept but used(!) car with conventional spot welding and seam sealed treatment would last for a long time time - 20 plus years. How much longer must your car last?

Thanks to DeliveryValve for the glue links though - interesting option.
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  #4  
Old 10-09-2011, 03:25 PM
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Quote:
Originally Posted by DeliveryValve View Post
I've used this stuff to bond quarter panels. 3M 8115 adhesive with good results with minimal spot welding while wet. The glue is very tough once cured. I think it would be a good solution to your rocker panel. ..

.
I just re-read the data sheet of 8115.

Quote:
This product is not
intended to bond structural components of a vehicle such pillars, rockers, or frame members. If doubt
exists as to whether a particular component is structural, then that component should be welded.
The rocker is most likely a structural component. But I think a combination of minimal spot welding the adhesive would still work. Plus using a product like Dinitrol that Army mentioned above should work out.




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  #5  
Old 10-09-2011, 08:03 PM
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If you need to pretty much rust proof an enclose area ..... FluidFilm is sold in the states by farm supply and tractor dealers for that kind of thing..
Pretty much pure lanolin... spray through small holes into fixed area and seal the holes....
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  #6  
Old 10-09-2011, 08:17 PM
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Quote:
Originally Posted by leathermang View Post
If you need to pretty much rust proof an enclose area ..... FluidFilm is sold in the states by farm supply and tractor dealers for that kind of thing..
Pretty much pure lanolin... spray through small holes into fixed area and seal the holes....
Doesn't sound like it's just for you Texas clodhoppers:

Fluid Film® | Corrosion Preventative, Lubricant and Rust Inhibitor
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  #7  
Old 10-09-2011, 09:58 PM
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do you have photos of the panels that need bonding? I've got a car nearly completely stripped down, and could offer some insight if you are in doubt.

welding has certain strengths and some weaknesses... fire from the undercoating is a possibility that does not exist with epoxies...
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  #8  
Old 10-10-2011, 04:35 AM
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Quote:
Originally Posted by vstech View Post
do you have photos of the panels that need bonding? I've got a car nearly completely stripped down, and could offer some insight if you are in doubt.

welding has certain strengths and some weaknesses... fire from the undercoating is a possibility that does not exist with epoxies...
I've been burning off old W123 undercoating with a blow torch and I'm surprised at how much heat is required to keep it burning - don't get me wrong that evil stuff smokes like a %^&%$^&*$^* but it doesn't keep burning that easily.

Was the same stuff used earlier on the W114 / W115s?
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1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1992 W201 190E 1.8 171,000 km - this one should be the daily driver

Don't leave that there - I'll take it to bits!
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  #9  
Old 10-10-2011, 04:40 AM
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Quote:
Originally Posted by DeliveryValve View Post
...
The rocker is most likely a structural component...
I'd say it is most definitely a structural component. Removal of the floor or the roof will bust that egg shell in two (or three or four!)
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1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1992 W201 190E 1.8 171,000 km - this one should be the daily driver

Don't leave that there - I'll take it to bits!
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  #10  
Old 10-10-2011, 09:26 AM
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Rockers structural?

Actually I would be surprised if the outer rocker panels were considered as structural on a w115 or w123.

As far as I know, on most cars they are not. For example, rockers are the one area where many bodyshops will still fabricate repair sections as they can use thin metal stock to do so.
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  #11  
Old 10-10-2011, 09:48 AM
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when in doubt replicate what the factory did, weld it. The rockers may not be "structural" in the strictest form, I would argue they are, but they sure do add significant strength to the rigidity of the vehicle over all. Bonding adhesives are fantastic and I don't doubt that they would work but you cant go wrong with welds. if your concerned about rust creeping in over the next 40 years, keep the car maintained and clean, that will help slow the re-rusting process.
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  #12  
Old 10-10-2011, 10:06 AM
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Thanks for the advice, folks.

It never occurred to me that perhaps the rockers could add anything structurally. The raw replacement panels seem quite flimsy and the actual frame is hidden beneath, so one could be excused for ignoring what impact, if any, they have on rigidity.

I'll talk it over again with the body dude.

I'd not have dwelled on it if this were a '77 or newer 240. But given the scarcity of W115 parts now, I shudder to think at the effort and expense of sourcing body panels in 15-20 years. I'd like to do the best thing now to extend this quasi restore out to benefit not only myself, but any future owners as well.
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  #13  
Old 10-10-2011, 02:21 PM
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Quote:
Originally Posted by Zacharias View Post
Actually I would be surprised if the outer rocker panels were considered as structural on a w115 or w123.

As far as I know, on most cars they are not. For example, rockers are the one area where many bodyshops will still fabricate repair sections as they can use thin metal stock to do so.
I'm 90% sure the same thickness steel is used on the floor pan and the sills / rockers / longerons (whatever you want to call them!) on a W123. I think the roof is also the same thickness. These flimsy bits of steel are made stiff by pressing funny shapes in them, punching holes in them with a lipped edge, bending them into awkward positions and tacking them together.

So far I've identified slightly thicker steel plates on the front of the W123 down the side of the car behind the front wings / fenders just below those horrible rot prone bonnet / hood spring pockets. The rest of the body structure from the fire wall back seems to me to be of the same gauge (thickness) steel. (Even the long beam that the differential is bolted on - but I'll check that)

Only at the front can I find real thick "reinforced" bits such as the two beams that hold on the lower cross member for the engine mounts, and the two little out rigger bits that lots of people recommend as lifting points instead of the more flimsy looking jacking holes in the rockers... oh yes and some almost after thought add-ons for the gear box mounting points!

My point being? Compared to a 1950s ladder chassis it all looks like it will bend by the time it reaches the first corner!
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1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1992 W201 190E 1.8 171,000 km - this one should be the daily driver

Don't leave that there - I'll take it to bits!
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  #14  
Old 10-10-2011, 03:51 PM
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I've seen those panel adhesives work very well for that kind of repair. As for concerns about strength, I'd put them to bed. Thats some strong stuff!
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  #15  
Old 10-10-2011, 05:39 PM
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I've used fiberglass repairs--very successfully--in rocker panels and floorboards. It helps prevent further rust, and I never had issues with them failing. I just used multiple layers of fiberglass cloth to build up strength.
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