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Old 09-29-2020, 12:19 PM   #1
spock345
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Default Rusty floor pans, patch or replace entirely?

I've finally gotten around to doing the floor pans in my 122. The only real holes and thin metal are on the outer edge. The inner edge where it meets the transmission tunnel has some scaling surface rust. I thoroughly stabbed it with a screwdriver and it didn't punch through or flex. Should I replace the whole pan or just weld in a patch? This is not the first time I have welded in a rust patch but it is the first time I have been staring down major floor pan work.

I plan to apply some POR 15 either way as I have most of a can left over after doing some work on the trunk and need to use it before it goes bad.

Has anyone added some sort of drainage to their Amazon's floor to avoid the rust problem? If so how?
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Old 09-29-2020, 12:44 PM   #2
dl242gt
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If you have enough good metal near the area of the rust hole. Then I'd just patch the bad area. There may be some rust patch panels available. I'd check with VP autoparts or Skandix to see what is available.
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Old 09-29-2020, 12:57 PM   #3
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Originally Posted by dl242gt View Post
If you have enough good metal near the area of the rust hole. Then I'd just patch the bad area. There may be some rust patch panels available. I'd check with VP autoparts or Skandix to see what is available.
I've already got the front pans from VP. Mostly because I didn't want to shape sheet steel to have the strengthening ridges. So I was just going to cut the patches panels out of those.

Is there any advantage to lap welding vs butt welding in this case if I use a good weld through primer?
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Old 09-29-2020, 01:07 PM   #4
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With lap welding the patch in. You can get a panel edge flanger tool and make a nice flange to meet up with the sheet metal. Sometimes the inner rocker is rusted and it's helpful to install a 90 degree piece going from the floor up the inner rocker to add strength.
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Old 09-30-2020, 12:16 AM   #5
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Originally Posted by dl242gt View Post
With lap welding the patch in. You can get a panel edge flanger tool and make a nice flange to meet up with the sheet metal. Sometimes the inner rocker is rusted and it's helpful to install a 90 degree piece going from the floor up the inner rocker to add strength.
I went out to the car today and cut some of the rust out. The rockers are still solid but there was some surface rust under the undercoating on the inside edge where the floor pan bends and is spot welded onto the rocker. So I will be cutting the spot welds in that spot to wire wheel away that rust.

Thanks for the tip to check. It seemed good from my poking until I hit that bit of undercoating. Small spot though, I seem to have caught it early.

Last edited by spock345; 09-30-2020 at 12:32 AM..
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Old 09-30-2020, 02:58 AM   #6
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Originally Posted by spock345 View Post
I went out to the car today and cut some of the rust out. The rockers are still solid but there was some surface rust under the undercoating on the inside edge where the floor pan bends and is spot welded onto the rocker. So I will be cutting the spot welds in that spot to wire wheel away that rust.

Thanks for the tip to check. It seemed good from my poking until I hit that bit of undercoating. Small spot though, I seem to have caught it early.
The rust normally is worst on the inner rocker (sill) where the floors joins the A pillar area. The inner rocker can get a bit rusty where the outriggers join as well.

If patching I'd cut the sections out and butt weld in new bits leaving a 1mm gap around the edges to minimise distortion and to get good pen. You can get really good floor repair panels still for the Amazon and welding in new ones isn't a big deal, the biggest part of the job is probably getting the old one out neatly. You can then also check the chassis sections and treat them if required. But if it just needs a few small patches which sounds like the case then not really warranted.
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Old 10-01-2020, 12:29 AM   #7
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The rust normally is worst on the inner rocker (sill) where the floors joins the A pillar area. The inner rocker can get a bit rusty where the outriggers join as well.

If patching I'd cut the sections out and butt weld in new bits leaving a 1mm gap around the edges to minimise distortion and to get good pen. You can get really good floor repair panels still for the Amazon and welding in new ones isn't a big deal, the biggest part of the job is probably getting the old one out neatly. You can then also check the chassis sections and treat them if required. But if it just needs a few small patches which sounds like the case then not really warranted.
I have discovered the challenges of getting out the pans neatly. I found some pin holes above the frame members on the passenger side that I didn't notice before. A bit of surface rust on the inside. So that pan is coming out entirely to make sure it doesn't get bad in the future. I have a can of weld through primer and some sand paper ready. The drivers side is fine. The spot weld cutter I have leaves some small marks and I have accidentally drilled clean through in one spot where the spot weld wasn't well aligned with the frame rail. Might have to fill in a spot or two before welding in the repro panel.

I have made a patch on the driver's rear pan, not a fun time trying to butt weld that in with crappy wire in the welder. Got better wire and stitch welding in a patch is going much better. Still had to use the grinder to clean it up. I am not good enough yet to do without it. So it is back to some practicing until I can minimize my grinding work. I am very glad this car has so much bracing beneath the floors unlike some period american cars I have seen (Novas and Falcons).
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Old 10-01-2020, 02:15 AM   #8
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A plasma is a nice tool for this job. Best to cut the floor pan out as much as possible and around the spot welded areas. Then drill the spot welds and use a decent wood chisel to separate the spot welded area. On the tunnel side leave a strip along the outer edge to plug weld the floor pan to, you can then also stitch weld the floor to the tunnel as well. Easier than trying to get a nice butt weld. I Tig or oxy weld the front floor to the rear floor. The floor is a nice job to progress on from welding in patches.
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Old 10-01-2020, 01:27 PM   #9
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We have 2 different styles of spot weld cutting tools.

1 style has a drill bit and the other has a spring loaded centering pin.

The drill bit style is easier to use as the drill bit keeps the tool in place when removing the spot weld, but the spot weld cutting portion only has 2 cutting edges and are prone to breaking and once broken the tool can't be used.

The spring loaded version has a replaceable cutting bit with multiple teeth and are double sided so 1 bit has 2 sets of teeth and can be flipped over for use. The problem with this style is getting the teeth to start cutting in the correct spot. Center punching is critical to doing a clean job of removing spot welds with this tool. The other drawback to this tool is it only cuts around the spot weld so you have grind off the remnants of each spot weld while the other tool cuts a hole which removes the spot weld, but you have to fill a hole.
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Old 10-01-2020, 06:27 PM   #10
dl242gt
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An air chisel will separate spot welds.
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Old 10-04-2020, 08:06 PM   #11
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Quote:
Originally Posted by planetman View Post
We have 2 different styles of spot weld cutting tools.

1 style has a drill bit and the other has a spring loaded centering pin.

The drill bit style is easier to use as the drill bit keeps the tool in place when removing the spot weld, but the spot weld cutting portion only has 2 cutting edges and are prone to breaking and once broken the tool can't be used.

The spring loaded version has a replaceable cutting bit with multiple teeth and are double sided so 1 bit has 2 sets of teeth and can be flipped over for use. The problem with this style is getting the teeth to start cutting in the correct spot. Center punching is critical to doing a clean job of removing spot welds with this tool. The other drawback to this tool is it only cuts around the spot weld so you have grind off the remnants of each spot weld while the other tool cuts a hole which removes the spot weld, but you have to fill a hole.
I have some of those spring-loaded items and their associated parts in my menagerie.

The set which'd probably be best for the work here is the Blair Rotabroach kit #11090. Got mine to drill out spot welds, and it works great anywhere you can center-dimple the material to be cut out/through...

More info and a quick usage video at the company site:

https://shop.blairequipment.com/Frac...it-p/11090.htm

Available @ Summit Racing for a good price ;)

Cheers!
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