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Stiffening a FB Chassis

Old 10-19-05, 05:06 PM
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Stiffening a FB Chassis

I know that the FB chassis is already stiff for the time that it was produced, but i'm looking for a way to stop the creaks and groans that i hear everytime i go slowly over speed bumps or pull into/out of driveways. the groaning is coming from the rear of my car. I have the Racing Beat 3 point strut tower bar. I'm planning on seam welding my chassis after I fix all of my rust (it's confined to drivers floor pan and the passenger rear wheel well, just a tiny hole about 1/4" square), but for the time being can I do anything to stiffen my chassis? Right now i'm thinking about rivoting the seams to make them seem as one. If i go this route, i'm going to use 3/16" Aluminum pop rivots, the same rivots that i am using to cover the factory drain holes in the driver and passenger floor pans, sealing them with 100% Silicone Caulk, clear in color, paint under it with Rustolem Flat Black, and then use some black rubberized undercoater.

Would this stiffen the chassis enough to justify the work, or am I just wasting my time? Is the Aluminum going to be strong enough to not shear under the stress of the chassis flexing and the seams shifting?
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Old 10-19-05, 11:11 PM
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stitch welding and roll cage will stiffen it up, but the groams are from age and stretch of the metal.
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Old 10-19-05, 11:23 PM
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I'm going to be taking a welding class this spring at the local community college, and i'm probably going to be buying a Lincoln Electric wire feed MIG welder, does anyone have any expierence with Lincoln Electric welders? What should I look for?
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Old 10-20-05, 12:12 AM
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LE's are good welders. I have a rebranded LE MIG, and it's a nice unit. Unfortunately, when it was rebranded they took all the settings off and instead of amps it's just some arbitrary number. But, it welded some 1/4" steel no problem, so that's cool.

As far as stiffening it up, your only option is to put a cage in it. Strut bars are kinda like pissing in the ocean. The folks that make them and the folks that love them won't tell you that, but it's true. They're all too candy-assed to do much good. Sadly, my racecar makes the same noises. I don't think they're necessarily the noises of bending... when the plastic in the roof starts popping like in a Miata then you know you've got too much chassis flex.
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Old 10-20-05, 07:55 AM
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I have a nice hardmounted tower brace and it did make a bit of a difference, also had to find a nice level ground to install it, if the car was sitting uneven the bars would come up short so everything is held tight. I don't go with a cage because I can't have one in the class I run w/ AutoX.
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Old 10-20-05, 05:33 PM
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A roll bar would probably help quite a bit. On an FB, it bolts on the floor behind the seats, and to the rear wheel wells. I advise getting one with a bolt in cross brace, so the passenger can recline with it out. If you get a roll bar, be sure to check under anything where you are going to drill. Don't ask me why i know this
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Old 10-25-05, 10:36 PM
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I seam welded my FB and had good results. Plan on going through a couple spppols of welding wire and several evenings. Welding upside down isnt fun dont ask how I know this..lol. I sand blasted away the seam sealer before welding. After welding I sprayed on undercoating. All my work was done under the car. The erea that seems to help the most is seam welding the transmission tunnel but you have to remove the tranny to do this. I also added U channel steel to the main unibody frame like supports under the car. This was a extensive amount of work but...I can now jack up the car in the front and both tires on that side come off the ground. Open any door with no dragging or catching on the door catch. I know it has helped but how much I cannot say. Only cost was the welding wire and time so I decided to do it.
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Old 10-25-05, 10:43 PM
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Originally Posted by custom13B
I seam welded my FB and had good results. Plan on going through a couple spppols of welding wire and several evenings. Welding upside down isnt fun dont ask how I know this..lol. I sand blasted away the seam sealer before welding. After welding I sprayed on undercoating. All my work was done under the car. The erea that seems to help the most is seam welding the transmission tunnel but you have to remove the tranny to do this. I also added U channel steel to the main unibody frame like supports under the car. This was a extensive amount of work but...I can now jack up the car in the front and both tires on that side come off the ground. Open any door with no dragging or catching on the door catch. I know it has helped but how much I cannot say. Only cost was the welding wire and time so I decided to do it.
thanks for the positive feedback. I have full access to a 10,000 pound lift, so jacking up the car is not a problem. I'll probably have my grandpa weld the seams in the tranny tunnel this winter when I swap my tranny out (it's a manual and it slips hardcore) this winter. He's got an ancient arc welder, but he's really good with it, so i have no problem asking him to weld it up. Right now with my RB 3-point strut tower I can jack up the front left corner of my car, and the front right and left rear will come off the ground, and both doors will open with ease. Right now i'm pretty worried about how much rust I found in my drivers seat pan/under the seat mounting piece of metal.
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Old 10-26-05, 09:45 AM
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An ancient arc welder (stick style) is usually too powerful to weld the thin 0.025" thick sheet metal that the floor of the SA & FB chassis are made of. He won't be able to do anything but burn holes.

To do all the seam welding they are talking about, you have to strip the car down to bare, clean metal; everything that can be unbolted must be unbolted, and then all the undercoating, paint, and seam sealer must be removed. The amount of work required to do this is more than you think.

Also check the body area where the upper control arm attaches to the body. This area is prone to rust too.
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Old 10-26-05, 12:17 PM
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Don't weld on the car with it on the lift. Make sure the weight of the car is going through the normal suspension points/springs/struts. Otherwise you may end up with a nice stiff but twisted chassis.
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