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I recently bought a 1975 280z. The floors are completely rotted and most of the frame has rot holes.

So I've decided to build a tube chassis for it and put a V8 in it. This will be the first car I ever built a tube chassis for, any advice or tips would be appreciated.

 

7A26CE13-9040-4D8A-A22C-3ED96E4AEC99_zps

 

257F6E0A-201E-40C9-B369-0EF09DB095E9_zps

Edited by mjp147
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My advice is don't make a full tube chassis your first build. 

The beauty of that advice is in the simplicity. 

 

For real though. There are some awfully quick stock chassis Z's out there. I would spend the tubing money on a set of baddog frame rails and a set of floor pans. That's me. IDK. Post your progress. 

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My advice having gone down this road is that if you want to make a tube chassis don't start with an actual car.  Just measure out the big stuff on the floor or your build table and start from there.  Ship in a bottle construction will take 3 to 4 times longer and you run the risk of copying issues from your base car (I would know, my first tube Z chassis is now hanging on my shop wall as an art project).  If you really do want to do this you might consider a slightly different track.  Cut off the front end and make it from tube.  That will take less time and the car won't be down so long.  Then when ready do the rear.  

 

If you're going to do this you need to have a plan on what it is that you want to change.  You also need to be very careful that you don't fall into the trap of using too thick of tube or your tube car will weigh more than a unibody one.  People may laugh at that but when you add up everything needed to complete the car you may find that is true.

 

Cary

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My advice having gone down this road is that if you want to make a tube chassis don't start with an actual car.  Just measure out the big stuff on the floor or your build table and start from there.  Ship in a bottle construction will take 3 to 4 times longer and you run the risk of copying issues from your base car (I would know, my first tube Z chassis is now hanging on my shop wall as an art project).  If you really do want to do this you might consider a slightly different track.  Cut off the front end and make it from tube.  That will take less time and the car won't be down so long.  Then when ready do the rear.  

 

If you're going to do this you need to have a plan on what it is that you want to change.  You also need to be very careful that you don't fall into the trap of using too thick of tube or your tube car will weigh more than a unibody one.  People may laugh at that but when you add up everything needed to complete the car you may find that is true.

 

Cary

 

Any pictures or drawing of how you did yours that I could see?

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I am also in the middle of building a tube car.  Not for the faint of heart!  If you search the classifieds I think there still are some pictures of the partially finished shell I purchased from Chris Leone.  He had already completed a full roll cage and front end.  I ended up redoing most of the front clip and I'm now finishing up the floor, trans tunnel, firewall, etc. Slow going when you only get maybe 6 hours/week to work on it.  Maybe some day I will start a build thread on Hybrid.  Eventually it will become a IMSA GTU tribute car.

 

A lot depends on how much you need to replace.  Most of the rear of my car was intact, but no floors, firewall, or front.  If you can save/restore/reinforce the strut towers and frame rails I think it makes an easier project.  Brace everything out before you start cutting out panels.  That is assuming you are not building a race car.  The project gets a lot more involved if you need to locate and square suspension mounts, then you need to build up on a flat plate.  And you start thinking about all those compromises you might like to fix like Tube80z mentioned.

 

You can probably do it all with square tubing if you don't put in a cage.  But I found I can lighten things up quite a bit since I have the cage providing structure.  Either way plan way way ahead on what you want to do and don't "build as you go".  And you had better know how to weld and how to identify a good or bad weld.

 

Google for the MGB tube build thread.  Might give you some ideas of what to do and not to do.  Like mentioned above, he built up the entire car and it came in at 2400# or something like that.

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A full tube frame car is advanced fabrication, 8 or 9 on a 1-10 scale. I first did 3 full stock restorations that included extensive rust repair, then moved on to minor and major modifications including engine and suspension swaps, before (on about my 6th car) I did my first full tube frame. And that was just a simple ladder frame that was copying the existing ladder frame. A scratch designed built tube chassis was only after that.

 

No matter how rusted your Z is it will take you 3 to 4 times as long and it will be 2 to 3 times as expensive to build a tube frame car. And you will end up with something that's only really good for the race track if even that.

 

A tube frame car needs a roll cage and roll cages are only made with round tubing so you need a $400 bender.  Also a hand held power band saw, Mig welder, grinders, sanders, drills, drill press, jig saw, air compressor.

 

The easiest way is to start with some plans. Typically people don't give those up so you have to make your own. You'd be lucky if you could even get someone to sell them. 3D cad is the best but it can be done on paper. Another thing that would help is to be near someone that has a tube frame Z race car that would let you measure.

 

I would just fix what you have. You probably got it for less than a rust free car and you can spend some sweat equity to fix it and gain some knowledge in the process. To do it right it's still going to cost as much or more than a rust free car but you can spread the cost out over time.

 

(this is not my car, just an example picture)

post-38295-0-15152900-1446174422_thumb.jpg

Edited by Chris Duncan
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There are some very wise words in this thread.  Too often, our enthusiasm exceeds our capacities, with the result being frustration, dejection and failure.

 

My car has aspects of a tube chassis, in the sense that the front clip and floor/firewall were cut out, while the rest of the body was welded to a chassis-jig.  Separately, the roll cage was welded up, and then welded into the shell.  Then the floorpan was shortened, the firewall/floor welded back in, and finally the front-clip (with new structural members to account for the firewall setback.  Finally, more bracing was added to connect the roll-cage to the front and rear struts, and to the frame-rails in the engine compartment.  It's a forested warren of tubes; but even so, it's not strictly speaking a "tube chassis" because (1) the stock frame rails, albeit modified and reinforced, are still used; (2) the stock strut-towers remain, though they're braced in multiple points; (3) the K-member is mounted in the stock way (but no longer supports the engine); (4) the mustache-bar and associated rear suspension elements are also stock, although again, they're braced.

 

A true tube-chassis car would begin in a computer, with thorough structural analysis to determine tube placement and dimensions.  It would account for fatigue-loads and so forth, besides just suspension-loads.  It would presumably include some structural optimization, where an optimizer is wrapped around the finite-element calculation.  In other words, we are designing a brand new car.  We are not restoring or reinforcing a Datsun.  We are building something totally new, that superficially resembles a Datsun and carries a Datsun nameplate.

 

I'd love to see MJP147 succeed in his endeavor, especially since he's relatively local to me, and I'd be thrilled to visit and to offer spectator's approbation.  But for that very same reason, I'd urge caution and circumspection.  Start with a baseline car in better condition.  Renew the suspension components... bushings, shocks, brakes and so forth.  Maybe do a V8 swap.  Drive the thing, get comfortable with it... and on the nth iteration, think about the truly exotic stuff, like tube chassis. 

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One thing to keep in mind is locosts are mostly built from 1x1 0.065 tube.  0.125 at 2x2 will be strong, hugely overkill, and weigh a lot when you're done.  You could easily get away with the 0.065 for most of the frame and if you need to add strength in certain areas then bump it up to 0.095.  Good luck and have fun with this.

 

Cary

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Here's some progress pics of the build.

I've decided to make my frame out of 2x2x1/8. It may be a little heavy but I have no plans to race my car so I think it'll be okay. I picked this car up for $300 and thought it'd be a good car to learn on.

 

2 x 2 is a nice size to match to existing frame rails but go with a thinner wall, like .072.

 

I misinterpreted what exactly you were trying to build. It looks like a fun project with a low initial investment, and will definitely be a good learning experience.

 

If you get frustrated or run into problems just take a few days off, it works wonders for motivation.

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