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walkerbk

2x3 frame rails on a 280z

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Just checking to see if anyone has ever replaced the fame rails on a 280z with stock floors with 2x3 or 1x3 tubing. I know people do it with the replacement floors but mine are still in great condition. The problem I see is the stock floors have a large amount of contour to them to assist with rigidity. With that, a flat surface isn't just going to mate up.

 

I'm figuring after pulling the interior and cleaning out the old rails, put the new ones up there and hold them in place with a few jacks to help push up the low spots. Then from the inside bolt down through the  floor and the new frame rail some 1x1 tubing to pull any high spots down.

 

Again, I have been searching for a few days and hadn't found anyone yet. The main reason for replacement is I have finished an LS swap and would like to increase frame strength and do a 4 or 5 point cage.

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Sorry TUME, I haven't heard anything as of yet. It is really just the title that seems problematic.

The floors are supposed to be fairly flat, they have some strengthening beading on a couple places, but where the rail goes it should be pretty flat.

 

I've done 2x3 rails. They stick up in the cabin if you want to keep the bottom of the car above the rocker level. I would suggest 1x3 over 2x3 just because you could keep it under the car.

 

There are a couple users who have done full tubular frame rail replacements. I'll see if I can find a few of them.

 

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I don't mind using 1x3 or 2x3. Whichever ones fit better.

 

My understanding on the flooring is that the 240s had flat floors and the 280s had some flow to them. If this is incorrect, then I guess it's hammer bashing and all to get them flat.

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1x3 fits better of course, and 2x3 will be much stiffer. I think if you do like i did, rail can be lifted inside the car much more. So i would go to 2x3 and get stiffnes ( and much more work)

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I can't say as I do not have a 280z, but the replacement panels I looked up look to be straight. The frame rail caps from baddog my friend ordered for his 280z were also straight which probably indicates that the floor is suppose to be somewhat straight as well.

 

The 2x3 will sit up, my floor near the pedals is about 1 inch raised because I didn't think about that. I would recommend going with a 1x3 out of the two options. As TUME says the 2x3 will have more strength, but the 1x3 will still be quite a bit stronger than the stock ones depending on how you attach it to the floors and front and rear frame points. 

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i have a s130 which is always different than the older z's but i made my own frame ties by welding stainless 1x3 to the bottom of the frame rails. welded one end to the front main engine bay frame rail and connected them to the rear subframe. i have been beating on the car with a LS swap for 10yrs and they held the car nice and straight.post-24014-0-29617800-1477499436_thumb.jpgpost-24014-0-40173000-1477499409_thumb.jpg

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Hmm, leaving the rails open seems like a not so good idea, usually people connect the back of the rail to the rear subframe area, granted early Z cars don't have a subframe per say and you have a rear cross member so that may not be as applicable.

 

Additionally I thought welding stainless to mild was a pretty bad idea for anything structural. 

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3 hours ago, seattlejester said:

I can't say as I do not have a 280z, but the replacement panels I looked up look to be straight. The frame rail caps from baddog my friend ordered for his 280z were also straight which probably indicates that the floor is suppose to be somewhat straight as well.

Unlike 240Z replacement floors, the 280Z replacement floors I've seen are almost nothing like the originals. If you looks at the subframe connectors bad dog sells, the 240Z rail is flat, and has a flange, the 280Z rail has no flange, and is contoured to mate to the floor. There's a handful of bead rolls that do go over the frame rails, as well as a couple steps, curves, what have you.

 

As for stainless, I've seen lots of people suggest stainless for various things, and based on what I know about stainless (not a whole lot), I'd say stainless is sometimes used inappropriately, ie. stainless bolt kits. Stainless isn't just steel that doesn't rust. It has different properties that make it inferior to steel in certain applications.

 

I agree with seattlejester, leaving the ends open isn't a good idea. They're basically just dead weight if they're not connected to anything, and totally overkill for stiffening the floor. Honestly, I didn't even know you could weld stainless to mild, I thought you had to braze it.

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Posted (edited)

Didn't see the need to cap the end off the back, maybe you can't see it but there a block welded to the subframe that drops down and welded to the top of the bar... the front is angle cut and hammered up so it's wedge shaped...I have heard the same about stainless welded to steel but we Did use stainless wire ,primed and seem sealed it and it's been good for 10yrs. I'm always under the car doing things and would see if there was issue...its what we came up with for frame ties and I'm happy with them. Every time the car has been dynoed they use them for strapping the car down even.

Edited by G-Tech

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I just thought that the frame rails in the photo werent complete... never even thought someone would leavr them like that. 

 

As for welding to stainless steel and all, most stainless does not have the strength that mild steel does, but they can easily be joined. The proper way would be to use stainless wire as it will weld exceptionally to both metals.

 

Turbo 930: sounds like you have some dealings with the 280 floor. Do you think my method will work. Push up with jacks, pull down with bolts and a hammer where needed?

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@rturbo 930 Ah, I remember some steps cut out in the replacement rails, but I didn't really register them as curves, but yes they are in retrospect.

 

In that case you would either have to notch the beam or notch the floor. I think notching the floor would be easier of the two options, but pulling the high spots down forcefully does not seem like a good idea.

 

 

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Posted (edited)
3 hours ago, walkerbk said:

Turbo 930: sounds like you have some dealings with the 280 floor. Do you think my method will work. Push up with jacks, pull down with bolts and a hammer where needed?

I think out of the three, the hammer is the only worth while option. The floor material is fairly thin, so it doesn't bend that hard, but the bends it has are pretty sharp, some of which are bead rolls. If your floors and frame are in good shape, I'd actually just make up a sheet metal piece out of the same thickness to connect your current rails to the rear subframe. Not that I'm an expert, but I'm not really convinced that thicker metal is needed here, I think simply connecting the front to the back will be plenty. I think your roll bar is going to do far more for stiffness than the subframe will if done right. Look up John Coffey's suggestions for chassis reinforcement on a street car.

Edited by rturbo 930

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I slid my bad dog frame rails up as far as they would go and scribed them to fit the car. I had to cut almost the entire length. I think they're made to weld to the sides of the existing frame rails, not the floor, at least on the 280. I wanted mine to fit the floor. Just get some U channel, scribe it to the floor, and cut, cut, cut. 

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I used 2x3 and did perimeter frame, welded it to the rocker then did 90 over to frame rails in the front.  Gonna weld a tube from that 90 up  up to the strut tower and another to the back of the strut rod bracket (cut the lower part of the frame rail off) and another back at an angle  back to the frame rail. The floors were gone and had to come out anyway and I am planing on cutting out the outer rocker and fitting 2.5" exhaust into the recess for the side pipe look that isn't hanging off the car. The jegster hoop sits perfect on the rails and runs back to the rear strut towers and down to the rear crossover factory frame rail and the door bars will attach to the 2x3 frame rail. Should be pretty strong and add a ton of clearance under my slammed car(floor boards used to rub on everything.  

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I was looking at something like that earlier. My car is currently on stands and I always put a 1x1 square tube between them and the car to help distribute the weight.

The 1x1 fits up under the side very nicely with only the smallest amount showing. I'm thinking redo the rails as planned or add in 1x1(1x.5 wouldn't be seen at all) welded to the perimeter tied into the rails and the front/ back. 

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I did 1x3 subframes on mine but also replaced the floor pans with custom built ones that are flat on the bottom.  I replaced the front frame rails with 2x2 as well so the front tie in is different from stock rails.  Here's what mine looks like and we capped the open ends of the 1x3 with a piece of sheet metal welded solid.

 

 

DSCF0017.thumb.JPG.a847561f2ecfbe605995e02f6d73aba9.JPG

DSCF0018.JPG

DSCF0019.JPG

DSCF0020.JPG

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