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Jon's 2 year roll cage saga...


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Went out to see about fitting the seat. Kinda surprised at what I found.

 

I started by setting my Recaro tracks on the stock seat mounts and then setting the Ultra Shield seat on top of the old tracks. It seems like the seat is WAY too high, but that’s weird because the padding in the butt is only about 1†thick. But even at that my hair is brushing against the headliner. I did have a couple pieces of 1x4 wood in there so that added 3/4 inch to the height of the seat, but I’m really surprised that I’d need to go lower.

 

It looks like I’m going to need to completely remove the stock seat mounts and start over because they are too high. I've got some square 1" x .065 tubing that I can use to build a frame. I guess I can weld it to the rockers and the trans tunnel then maybe put a support underneath on each side to the floor.

 

Do I sound like I'm on the right track here? Anyone know of an easier way? Pics of seat mounts would be GREATLY appreciated...

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It looks like I’m going to need to completely remove the stock seat mounts and start over because they are too high. I've got some square 1" x .065 tubing that I can use to build a frame. I guess I can weld it to the rockers and the trans tunnel then maybe put a support underneath on each side to the floor.

 

Do I sound like I'm on the right track here? Anyone know of an easier way? Pics of seat mounts would be GREATLY appreciated...

 

I suggest you remove the adjustable tracks and set the seat up for yourself. But, most folks don't want to do that...

 

Take your 1" square tubing and cut one side off so its a U-channel. Contour the open end so it fits tight down on the floorpan and connects to the rocker and the tunnel while keeping the top surface sqaure and level side-to-side. Stich weld the U-channel to the floor pan, rocker, and tunnel. Drill holes in the top big enough to get a 3/8" nut through the opening. Weld a 3/8" nut to a 1/2" washer, insert the assembly nut down into the hole, and weld the washer to the top of the 1" tubing.

 

Tip: Order 3/8" four corner weld nuts from McMaster-Carr and 1/2" uncoated metal washers.

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I suggest you remove the adjustable tracks and set the seat up for yourself. But, most folks don't want to do that...

My wife actually races the car every once in a great while. I'd like to keep it so that she could drive when she wanted. It's really hard to get her out there, but she LOVES it when she goes. She actually spun the car at Buttonwillow once. I was so proud... :)

 

Take your 1" square tubing and cut one side off so its a U-channel. Contour the open end so it fits tight down on the floorpan and connects to the rocker and the tunnel while keeping the top surface sqaure and level side-to-side. Stich weld the U-channel to the floor pan' date=' rocker, and tunnel. Drill holes in the top big enough to get a 3/8" nut through the opening. Weld a 3/8" nut to a 1/2" washer, insert the assembly nut down into the hole, and weld the washer to the top of the 1" tubing.

 

Tip: Order 3/8" four corner weld nuts from McMaster-Carr and 1/2" uncoated metal washers.[/quote']

So mount the seat an inch off the floor? That's going to be LOW. I guess that's good for center of gravity. How about not cutting the tubing into a U, but instead cutting the floor where the bump is in the middle then welding that part from the bottom?

 

Good tip BTW, I like that way of securing a nut inside the frame rail.

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but instead cutting the floor where the bump is in the middle then welding that part from the bottom?

 

Don't cut the floor. What you're building is a box with the floor as one side. Look at how the factory seat mount is built and you'll see that they went to great effort to keep from cutting the floor.

 

What would be even better would be to build a U-shaped channel with flanges that have holes punched in them for spot welding to the floor. The edge of the flange can be stich welded and the flange holes can be filled as spot welds.

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Why can't I just stitch the tube to the floor? I guess I'm not getting the importance of not cutting the floor, especially if it gets welded back to the tube.

 

Had a little brainstorm after your first response though. I "unwelded" my recaro sliders and I think I can use them. They have a piece at each end that bends down that has 3 height adjusting holes in it. So I figure I can weld a piece of the square tube to the floor and trans tunnel at the proper spacing to use the old sliders. Then I can weld the appropriate nuts into the tubing using your previously described method. It will still call for the tubing to be a bit off the ground though, probably 1/2" or so. I understand what you mean about attaching the bracket to the floor all the way across. I do have a bunch of sheet metal. Wondering if I couldn't weld that to the square tube and to the floor across to spread the load along the floor...

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Why can't I just stitch the tube to the floor? I guess I'm not getting the importance of not cutting the floor, especially if it gets welded back to the tube.

 

You're building a box right? Why do you need two walls on one side of the box?

 

Think of the floor as a shear panel (which it is). Cutting the panel across its width and putting a tube in there turns it into two shear panels with the tube as one side of both panels. You're creating a place where loads are concentrated to a 1" square .063" wall tube. It would be better to augment the shear panel with a tube attached to it then to cut the shear panel.

 

That's my thinking at least. Without any specific load numbers on the floor its really just a gut feeling with no tech to back it up. Just a monkey see engineering design based on what Nissan did with the factory seat mounts.

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You're building a box right? Why do you need two walls on one side of the box?

Because I don't have an appropriate saw to cut the tube lengthwise, and with the tools I have it would be such a PITA that I'd rather just weld it in as is.

 

Think of the floor as a shear panel (which it is). Cutting the panel across its width and putting a tube in there turns it into two shear panels with the tube as one side of both panels. You're creating a place where loads are concentrated to a 1" square .063" wall tube. It would be better to augment the shear panel with a tube attached to it then to cut the shear panel.

 

That's my thinking at least. Without any specific load numbers on the floor its really just a gut feeling with no tech to back it up. Just a monkey see engineering design based on what Nissan did with the factory seat mounts.

I think I've got a bit of a plan figured out. I'm going to do the 1" tube with a small maybe 1.5 x 1.5 plate on the ends, then maybe run one little pedestal to the floor on either end to support the vertical load, with another 1.5 x 1.5 plate on the floor.

 

I just got off the phone with a friend of mine who has made similar mounts on his 510s in the past with no trouble.

 

If anyone has a better idea I'm all ears.

 

One more question for you John, since I have your attention. How big does the plate need to be where I attach the roll bar tube to the rear strut tower?

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I'm not completey sure I follow. Are you putting this tube across the car or lengthwise?

 

If across I would use sheet metal to hook to the floor just like the stock piece, similar to what John mentions above. But I'm may not be following what you're doing here.

 

For the tubes I try and do 4 times the area of the tube. Not sure why but somewhere along the line I picked that up.

 

At least one of us is out in the shop working :-)

 

Cary "stuck at work"

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On the seat mounting I'm talking about 2 square tubes across from the rocker to the transmission tunnel. The sliders have a long frame which will straddle the two tubes lengthwise. At the end of the sliders is a piece of metal that bends down about 2" and has 3 holes in it so that you can put raise or lower the seat, or change the angle by mounting to the bottom hole in front and the top hole in back, etc. I don't want to go quite so low as to put the 1" tubing on the ground, so instead I'm thinking about mounting it up off of the floor about an inch, then making little supports that go down to the floor so that the vertical load isn't really supported by the transmission tunnel.

 

Does that make any sense? I wish I could upload pics...

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yep, that makes sense. I would close the gap across the lateral tubes to the floor rather than just use a couple of stands. That makes the floor a shear panel as Jjohn mentions. It would seem like it would be harder to rip out too.

 

Figure in a wreck (worst case) that you might see some rather large forces on those mounts. And having more area will lower the load, or some my feeble thinking goes.

 

Cary

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How big does the plate need to be where I attach the roll bar tube to the rear strut tower?

 

SCCA says .080 minimum thickness, no more then 100 square inches, no longer then 12" on one side, and no shorter then 2" on one side. If you're going to the top, cover the whole top of the tower. If you're going to the front side, something 4" x 8" should be fine. If you wrap the plate around the tower it will help witht he strut tower brace.

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If I were to follow Cary's basic guidline then the area of the 1.75" tubing is 3.14 x .875 x .875 = 2.404 in sq. If I went 4x that, I'd need 9.6" sq. I have some 3" wide strap .120" and I could do a 3 x 3.5 and get 4x the area. That seems awful small, doesn't it? Might go 3" x 8" or maybe 3 x 6.

 

I already have the strut tower bar welded in so I kinda want to leave that area alone.

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Pretty nasty work getting everything ready for welding. People sometimes wonder why I charge what I charge to build a roll bar. The welding is only a small part of the work involved. Its like painting a house, getting the paint on is the easy part.

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If I were to follow Cary's basic guidline then the area of the 1.75" tubing is 3.14 x .875 x .875 = 2.404 in sq. If I went 4x that, I'd need 9.6" sq. I have some 3" wide strap .120" and I could do a 3 x 3.5 and get 4x the area. That seems awful small, doesn't it? Might go 3" x 8" or maybe 3 x 6.

 

Reading this I see that I told you a lie. I don't do area. I've been doing 4 times the size. So for a 1.5 inch tube I've been doing a 6x6 pad. You wouldn't know I had a math degree :-(

 

I'll plug weld those too to make the stick better.

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