Jay Gadsby Posted March 18, 2015 Share Posted March 18, 2015 So, I have started getting deep into the rust repair phase of this project. My front frame rails need replacing, the normal frame rails from front to back as well. I am going to fabricate everything short of the rocker panels if at all possible My floor pans are rusted through, but only straight down the middle above the rails. Exception to this rule is where the firewall and the floor meet. I have the battery box cut out. Getting ready to cut out the front of the engine bay frame rail to create a new smooth firewall. Herein lies the question. Under the firewall and floor area it is two pieces of metal sandwiched in for about 6 inches into the floor area. I want to replace this all. Do I need to replace the two pieces of metal, meaning, do I need to weld in a floor patch, and a new firewall patch separate? I am running 16ga for all the patches. I have access to a rudimentary brake for bending. It would be nice to be able to run one piece from the firewall down and meet on the happy side of the floor pan. Thoughts, suggestions, bitches, gripes or complaints anyone? Quote Link to comment Share on other sites More sharing options...
rturbo 930 Posted March 18, 2015 Share Posted March 18, 2015 (edited) Why are you using 16g for the patches? Use whatever thickness the factory used - mostly 20g. It sounds like you have quite a bit of metal to replace, and if you use 16g for all of it, you're going to add quite a bit of weight. Edited March 18, 2015 by rturbo 930 Quote Link to comment Share on other sites More sharing options...
Jay Gadsby Posted March 18, 2015 Author Share Posted March 18, 2015 (edited) Mainly because it is what I could get my hands on. This car is getting the LS treatment, and is not a track car. It will be a road car with some track time (read very little). The difference in weight is a pound per square foot between .0359 (20 gauge) and .0598 (16 gauge) is 1 pound per square foot. I will just have to diet a little to make up the weight. And being a 71 240Z, this thing needs as much structural rigidity as I can throw at it. The only saving grace is that by some miracle the entire rear of the car is rust free (except the trunk sill which I already fixed). The battery box area and center of the floors are the main culprits. The front frame rails are being replaced with 14ga 2.5 square tubing. Should stiffen it all up well. Edited March 18, 2015 by Jay_Gadsby Quote Link to comment Share on other sites More sharing options...
rturbo 930 Posted March 18, 2015 Share Posted March 18, 2015 Thicker metal alone is not going to stiffen up your chassis in any significant way. John C has a good post on things you can do to improve stiffness in a street car. Shelve the 16g sheet metal for another project and get 20g. Sheet metal is not expensive, and you should be able to find it fairly easily. Quote Link to comment Share on other sites More sharing options...
Jay Gadsby Posted March 18, 2015 Author Share Posted March 18, 2015 Out of the 6 metal supply companies in my area, 6 do not carry anything thinner than 18. And that is a special order costing double the amount of the 16. Unless my car is in danger of being sucked into a wormhole because I used a .02" thicker metal on the firewall and floors, I think it will suffice. Barring my choice in metal, any input on the question of multiple layers being replaced with one layer? Quote Link to comment Share on other sites More sharing options...
seattlejester Posted March 19, 2015 Share Posted March 19, 2015 It is strange that a metal shop doesn't have 20 gauge, but we should move beyond that. If you are willing to work with 16 gauge then so be it. Just for reference 20 gauge is just much easier to work with, 18 gauge is not bad either, once you get to 16 gauge, you can't use a lot of the cheaper benders, hole punchers, automated shears, etc that make your life really easy. I used 18 and 20 gauge, I didn't have the dies to reinforce the fire wall so that got thicker steel, and the floor I overlapped so I think the 20 gauge is fine. It is mistaken to think that just replacing a small piece of one portion of the car with thicker steel will strengthen the rigidity of the vehicle. You could do the floor and firewall in one piece, but that would be a fairly large piece. I did mine out of 3 pieces. One for the firewall, one for the floor, and then another to round the joining area. Given that you are using thicker steel it may not be as problematic to use one piece, the concern is how you will make the bend from the firewall to the floor without stressing the metal too much. Quote Link to comment Share on other sites More sharing options...
Jay Gadsby Posted March 19, 2015 Author Share Posted March 19, 2015 I found one place about 45 minutes away that can get 20, we shall see if I am feeling adventurous. Most of the metal places around here are steel building supply places. A popular item in and around fort hood it seems. I will be using a plasma cutter to cut it, so that helps. The brake in have bends the 16 pretty well. It's only about a 50 degree bend to transition to the floor. So you are thinking a single piece with a small overlap would work where as the original piece has inches of over lap? It's all how it's welded in in guess as well. I know just adding stiffer metal does not necessarily mean stuffer panel, but compared to the wafer thin rusted out metal the PO drove around on for what seems an eternity worth of band aids and cover ups, anything will be an upgrade. Quote Link to comment Share on other sites More sharing options...
seattlejester Posted March 21, 2015 Share Posted March 21, 2015 I mean if you have the means to use it, then go for it, just know that know everything else is weaker then the new repair you made lol. If you have a plasma it should be easier as long as the cuts are clean or else lots of finishing work for the pieces. My brake was a cheap one and boy would it struggle bending 16. It would fold 20 gauge completely in half though. I built the frame rail first and welded my floor and firewall around it. I don't recall the overlap very well on the stock car since my floor was so far gone. I just didn't want to make the bend so I welded the firewall portion then the floor and let them meet up and then welded those and welded a piece to round it out so it wasn't at an abrupt angle. Could you take a picture of the area in question to refresh my memory? Quote Link to comment Share on other sites More sharing options...
Jay Gadsby Posted March 21, 2015 Author Share Posted March 21, 2015 It is true, the camera adds 10 pounds of rust lol. Battery box cut out, working on the frame rail so I can do the firewall, then the engine bay frame rail. The floor pan is solid everywhere except where the frame rails are. I am Sooo glad I made a rotisserie. This stuff on my back would be miserable. Quote Link to comment Share on other sites More sharing options...
seattlejester Posted March 24, 2015 Share Posted March 24, 2015 Oh, that overlap. Hmm I don't have nearly as much on mine anymore, but my floor is fully welded instead of spot welded. Can't offer any structural advice there, but if you are going thicker it should be ok. I would poke and prod all the sheet metal in the surrounding area, that frame rail section seems pretty far gone, and it would be easier to replace any adjacent material while you have it up on the rotisserie. Quote Link to comment Share on other sites More sharing options...
morbias Posted April 3, 2015 Share Posted April 3, 2015 (edited) There shouldn't be any area of the floor that has 6 inches of overlapping sheet metal. The fronts of the floors overlap the bottom of the firewall by about an inch so they can be spot welded on, and under that there is a small overlap where the frame rail sits as the frame rails are actually formed as double box sections in that area. Be sure to check them out as they have a tendency to rust out in that area due to the angle causing water to sit there, you might even have to cut some of the lower firewall out to access it. Also, that area is about as structural as structural gets because of the front end of the car wanting to pivot upwards on that point so make sure it's solid first before welding the floor on top of it. Edited April 3, 2015 by morbias Quote Link to comment Share on other sites More sharing options...
Jay Gadsby Posted April 6, 2015 Author Share Posted April 6, 2015 Gotcha. 6 inches may be a little bit of a fish story, but as you can see in the pic above, there is a definite overlap. Maybe it was another hack job by the PO, as it seems it was welded all the way down versus just spot welding. The plans for the frame rail to fire wall is fully welded 1" flanges on the firewall side of the frame rail(which is 14 gauge 2.5sq tube) Then the 1.5x3.0 tube will run front to rear 1/2" above floor level and angling upto the TC rod cup. Hoping it will be beefy enough. 1 Quote Link to comment Share on other sites More sharing options...
seattlejester Posted April 7, 2015 Share Posted April 7, 2015 Hmm with a 1.5 you might be able to leave all of it beneath the floor. I think my rail was 2 x 3 and it sticks into the cabin half an inch to an inch and is flush with the lowest point on the body. Quote Link to comment Share on other sites More sharing options...
Jay Gadsby Posted April 7, 2015 Author Share Posted April 7, 2015 Pics or it didn't happen! Flush would still work the way I am envisioning. Was just trying to keep the frame as high as possible for some sick stance lowering. Just kidding. slight drop is all that's planned. Quote Link to comment Share on other sites More sharing options...
seattlejester Posted April 8, 2015 Share Posted April 8, 2015 Blurry picture The lowest line is the exhaust Interior shot Quote Link to comment Share on other sites More sharing options...
Jay Gadsby Posted April 8, 2015 Author Share Posted April 8, 2015 Awesome! Thanks. Pretty much what I was picturing. Also found a new fountain of joy. PO riveted on the rear quarter/doglegs and bondoed the everyloving shite out of it all. At least it was fairly recent. The metal is still good, just need to drill out the rivets and then weld it all in. Seems I will be getting my welding degree on this car alone lol. Quote Link to comment Share on other sites More sharing options...
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