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 Post subject: Trans tunnel bracing
PostPosted: August 30, 2019, 1:00 am 
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Joined: March 18, 2008, 10:25 pm
Posts: 282
Location: Wasilla, AK
I'm getting ready to add bracing to the trans tunnel. I'm thinking of opposing the bracing from one side to the other. Anyone see a benefit or a problem with doing that?


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 Post subject: Re: Trans tunnel bracing
PostPosted: August 30, 2019, 1:12 am 
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Joined: January 11, 2017, 11:06 pm
Posts: 162
Location: Alberta
It might make the chassis twist when it wants to flex, or bow when it wants to twist. What's the reasoning behind it?


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 Post subject: Re: Trans tunnel bracing
PostPosted: August 30, 2019, 8:10 am 
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Joined: September 22, 2005, 8:12 am
Posts: 1742
Location: 4AGE in S.E. Michigan
If you are wanting to improve the torsional resistance of the tunnel member, the addition of a 2nd bottom and/or 3rd top diagonal attached at the intersection points will improve the design. There is no sufficient advantage in direction placement of the side diagonals in the tunnel. The one thing to consider in the design of the tunnel is the lower seat belt attachment brackets. Adding additional braces or diagonals between the outer side rails is a more effective use of material/wt relative to improving torsional resistance of the structure along with the attachment of the rear and front bulkheads. Also look at adding braces to the dash board attachment beam down to the tunnel [depending transmission linkage] to strengthen the open cabin area. After that you can look at diagonals in the floor area. Davew


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 Post subject: Re: Trans tunnel bracing
PostPosted: August 30, 2019, 9:52 am 
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Joined: October 24, 2008, 2:13 pm
Posts: 4191
Location: Carlsbad, California, USA
One thing I learned (too) late in my design and build is to watch the angles where diagonals meet other tubes. They are a real b*tch to weld.

For example, the tunnel diagonal in the foreground the upper left and lower right welds of the diagonal will be hard to weld.

There is no real loss of functionality to drop the left end down 3/4" (or 1") and the right one up the same amount. They will be much easier to weld.

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 Post subject: Re: Trans tunnel bracing
PostPosted: August 30, 2019, 9:12 pm 
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Joined: August 28, 2010, 7:53 am
Posts: 263
Lonnie - i use round tube for diagonals - much easier to get in corners


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 Post subject: Re: Trans tunnel bracing
PostPosted: August 31, 2019, 9:41 am 
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Joined: July 17, 2008, 9:11 am
Posts: 5535
Location: West Chicago,IL
I found that if I moved the diagonal's tip about 1/4" down and up the verticals away from the horizontals, I could weld without issues. Yeah, the wire stuck out of the gun a fair amount. YMMV.

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 Post subject: Re: Trans tunnel bracing
PostPosted: September 2, 2019, 2:22 pm 
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Joined: July 4, 2006, 5:40 pm
Posts: 1986
Location: Novato, CA
I don't see a problem with your cross-bracing but it seems like overkill. Sheeting the tunnel should add all the torsional stiffness you need.


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 Post subject: Re: Trans tunnel bracing
PostPosted: September 5, 2019, 11:03 pm 
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Joined: June 13, 2014, 11:55 am
Posts: 87
I went for Doble wall tunnel.
One 1.2 mm steel sheet stitch welded on that area and 1.5 mm Alu tunnel skin.
Overkill..
absolutely, but I was a little paranoid about my propshaft flailing next to my legs.


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 Post subject: Re: Trans tunnel bracing
PostPosted: September 6, 2019, 2:20 pm 
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Joined: July 4, 2006, 5:40 pm
Posts: 1986
Location: Novato, CA
I worried about that too until I git the driveshaft back from the driveline shop. All of 12" long. Not that it couldn't still do some damage but it didn't look all that scary. Anyway I sheeted my tunnel as well with 18 gauge up front and 16 gauge back by the driveshaft.


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 Post subject: Re: Trans tunnel bracing
PostPosted: September 14, 2019, 1:27 am 
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Joined: February 22, 2017, 10:47 am
Posts: 8
Location: Raleigh NC
This is just my humble opinion and is mostly personal preference, but when I am triangulating rectangular sections that are about 2x or more in length than their width, I usually try to avoid having long thin triangles by boxing the long rectangle into 2 or more roughly squarish section and then triangulating those. For example I would have a diagonal going from the top left corner down to the middle of the bottom horizontal tube, and then another diagonal going from the middle of the bottom horizontal tube to the top right corner, and also a vertical tube from top to bottom in the middle. i.e. like the middle of a Pratt truss. It uses more tube, but it makes a much stronger rectangle, both of the long tubes are supported at their midpoints, and it's a lot easier to weld. Just my .02, YMMV.

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 Post subject: Re: Trans tunnel bracing
PostPosted: September 14, 2019, 11:38 am 
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Joined: September 30, 2005, 1:28 am
Posts: 1295
Location: Sunny-Okanagan, Canada, eh?!
This is what I did on frame #2. But it's been hanging stagnant from the ceiling for the past 7 years or more.

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