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Old 02-22-2009, 08:44 PM
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Frame Design

What do you think?
Just rough plans I'll finalize the dimensions later.
2x3 Rectangular tube .120" wall
3" Z in the front adding a split section of 2x3 to taper the rail & act as a gussett
Leaning towards a 6" Z in ther rear
4 bars & coilovers on all four corners
2x2 .080" for the gas tank suround & center x member or should I go with 2x3 .120" for the x member?
Anything I should do differently?

Shane
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Old 02-22-2009, 08:57 PM
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Very nice.. I would build it... You don't really need to bring the bottom front all the way like you have it.But That's just me.
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Old 02-22-2009, 10:00 PM
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I realize this is a rough design, but I believe your front 4-bar frame mounting points will end up being lower than what you have drawn to have the bars level at ride height. That will require a mount for the lower bar below the frame and will eliminate the need for the extended gusset. Just kick the front up in a similar fashion as the rear. I would use 1 5/8" x .120 round tubing for the "X". It will give you the torsional stiffness you are apparently after and will take up less space under the car. I would also carry the "X" as close to the front and rear coil over mounts as possible for more chassis stiffness. Build the center lateral brace and the trans mount crossmember in the same round tubing also.

Move the rear panhard bar to behind the axle and make it as long as possible. If you can make the rear four bars the same length, it will help with controlling the pinion angle in bump and droop.

Andy
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Old 02-22-2009, 10:06 PM
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Yes I do have to agree with the front bars.They need to be level at ride height.Sorry I didn't catch that when I looked.Thanks Andy. The pan hard bar will work.But run it as far over as you can.Instead of putting it on top of the center chunk,Run it all the way across.to the axle tube.It looks like you can keep it high enough to clear the center chunk.You have enough room between the frame back there.Keep it level at ride height.

Last edited by NEW INTERIORS; 02-22-2009 at 10:13 PM.
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Old 02-22-2009, 10:30 PM
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I know I don't have to have the gusset tapering down that far, but it looks a little more like an old frame. I got the idea from Jonny Cola's coupe and the Live Wire coupe off of mad fabricators.



So flatter 4 bars, Closer to equal length on the rear,longer panhard bar.
Should the front 2x3 cossmember,and the 2 rear ones be enough in those areas for support?
Am I going too overkill on the center x member? Its just going to have a mild (300ish hp)small block Chevy & a 4 speed(remember the screwy od one from the early 80s) or a 5 speed.
It shouldn't be all that heavy.


Shane
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Old 02-22-2009, 10:42 PM
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If you can keep the rear bars the same it's better,But it has been run like you have them alot,And is still being ran that way.It will change the pinion angle a little.But not enough to worry.Just keep it close to the same..As far as the x-brace.I wouldn't have one in that car.You can put a good cross member with a loop in the back.And add the same brace's that i added on my willys frame,From the side frame rail to the cross member with the loop.And it will be very strong.If you understand a little bit about Triangulation.Then you will understand what I'm getting at.Then you will have a good transmissions cross member.And a cross member in the front.But some people like them.I only put them it a high hp car.Not so much for a driver.But everyone is different.This is a frame I built for my 32.It would pull the front up.Never had any problem's..

This frame was 2''x 3''x 3/16''.. And believe me it was way to stiff. The drive shaft was about 13'' long.It didn't like to spin the tires.The motor was so far behind the cross member.it had very good weight transfer.It would give you a He** of a ride out of the hole..
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Old 02-22-2009, 10:59 PM
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you may want to use 083 for you 2x3 tube frame. O83 is plenty strong. Also no need to cant your rear coils, you just increase the need for higher rate.
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Old 02-23-2009, 09:28 AM
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Quote:
Originally Posted by Chevrolet4x4s
So flatter 4 bars, Closer to equal length on the rear,longer panhard bar.
Should the front 2x3 cossmember,and the 2 rear ones be enough in those areas for support?
Am I going too overkill on the center x member? Its just going to have a mild (300ish hp)small block Chevy & a 4 speed(remember the screwy od one from the early 80s) or a 5 speed.
It shouldn't be all that heavy.
Shane
Adding an X in the center of the chassis is the most efficient way to torsionally stiffen a chassis. If you can, extend the X to the points where the suspension loads are introduced to the frame/body (at the coil-over frame attachment points in this case). I typically add bracing of this nature to every vehicle I build. Having a torsionally stiff chassis helps in many ways, expecially in open vehicles (roadsters etc.) to compensate for the body stiffness lost when the top structure is removed. The 2x3 rails will be strong enough for beam strength, adding the "X" will give you the torsional strength you need.

Moving the panhard bar lower in the rear (to the axle centerline if possible) will lower the roll center. That will help with more predictable handling characteristics. Increasing the length of the front panhard bar will help as well at that end.

Andy
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Old 02-24-2009, 04:07 PM
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I won't be able to extend the x member to the mounting points of the coil overs,due to the z's in the frame. I could add a 3rd rear crossmember & triangulate it there,and a midplate at the front if need be.
Would I be better off to use parallel leafs in the rear?Bed length will be 36",no more than 40" if need be. 4 wheel coil overs are not 100% set in stone.

Thanks
Shane
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Old 02-25-2009, 07:38 AM
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Extending the X to the spring pick up points is not always possible like you stated, I just try to achieve it when possible. Lateral crossmembers add little in torsional or beam strength, so adding some more would likely be a waste of time and space. In some cases a slight bend in the tube in the appropiate spot will get you closer to that goal of extending the X as far as possible. If you have the funds, the coil overs and trailing arm rear suspension would be preferable over parallel leaf springs. If you do decide to go with leaf springs, adding a panhard bar at or near the axle centerline is a good way to handle side loads and to lower the roll center of a hotchkiss type suspension.
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