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Old 09-09-2009, 12:00 PM
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Mounting seats/belts to wood floor

I don't know if this should be in the interior section or here, so moderators please feel free to move me. I checked Seat belt mounting points in glass car beforehand and it was placed here...

First off, I'm working with a 1935 Pontiac Coupe, obviously. It's pretty much the same as 35-36 Chevys, Buicks, etc, with the wood framing of the body. I am mounting seats with integrated belts (2002 Cadillac) and trying to figure out the mounting setup. I have seen both sides of the argument that you have to mount the seats and belts to the body of the car since the body moves at a different rate than the frame. However, with a wood framed body such as mine, how would that work? I'm not too keen on mounting the seats to the wood floors, especially since the belts are mounted to the seats.

Looking at the thread above, I see people saying that you should run a bar across underneath the floor to take the strain, however, if that's mounted to the frame, what happens when the body of the car gets pushed back and the frame keeps moving in a head-on collision? Since the steering column is mounted to both (more substantially to the frame though) which way would that move?

What is the best, and safest, way to mount these? Tearing out ALL the wood is not an option right now.

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Old 09-09-2009, 12:47 PM
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DO NOT mount the seats to a wood floor, that is totally insufficient, and unsafe. You must provide strong mounting points for the seat and integral seat belts. Usually in the case you have some 1-1/2" square steel tubing which is welded in the proper place between the fame rails to allow the seats to be bolted down to a suitably strong structure. This would require two square steel additions, one for front seat mount and one for the rear mount of the front seat.

Vince
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Old 09-09-2009, 12:51 PM
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Quote:
Originally Posted by 302 Z28
DO NOT mount the seats to a wood floor, that is totally insufficient, and unsafe. You must provide strong mounting points for the seat and integral seat belts. Usually in the case you have some 1-1/2" square steel tubing which is welded in the proper place between the fame rails to allow the seats to be bolted down to a suitably strong structure. This would require two square steel additions, one for front seat mount and one for the rear mount of the front seat.

Vince
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D O N ' T
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Old 09-09-2009, 01:05 PM
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Right, I'm not going to mount them straight to the floor. But the question is: Should I weld those braces to the frame or should they be left free to move independently of the frame? If the seats are mounted to the frame and the body moves back 6" or whatever, what happens to me? I'm moving into the steering column or dash.

I should also mention that the floor is not entirely wood. It has sheetmetal inserts and I will be adding more sheetmetal to the areas where there was wood before. However, the cabin frame is wood and the outer edge of the floors are wood, so all the steel floors mount to that outer piece of wood, which is bolted to the frame.
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Old 09-09-2009, 01:50 PM
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If you have a collapsable steering column that will help..when mounting the body to the frame use a through bolt with a vibration isolator which will limit any movement of the body relative to the chassis. Something like the universal motor mounts from speedway or others and of course you can fabricate those yourself if you like. then the seats and belts are mounted to secure metal structural points within the body..requires some thinking and mods to the body but it is a hot rod so that is OK..

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Old 09-09-2009, 04:35 PM
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Your worrying far too much about body movement relative to frame movement.....it's just not a problem.

Vince
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Old 09-09-2009, 08:27 PM
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What about using a piece of c-channel all the way across the floor? It would be able to run through the floor at points throughout the floor and not to the frame, but it will still have to sit inside of the frame rail. That would allow fore-aft movement with the body but not vertical in case of the absolute worst case.

Thoughts? I'd like to get Techinspectors thoughts, as he has posted in several threads before about safety issues...
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Old 09-13-2009, 05:10 AM
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NHRA dictates that a minimum 2" x 2" x 0.083" wall thickness steel tubing be installed between framerails at the back of the seat for proper driver seatbelt installation. I'd use one at the front of the seat and one at the rear if it were my car, as 302 Z28 said.

Stop worrying about frame/body movement. Nail the body to the frame at minimum 6 points with minimum 3/8" bolts and re-inforced body mounting points as OneMoreTime said. I don't know whether the car used plaited canvas strips between body and frame or if it used insulators, but you can figure it out.

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Old 09-13-2009, 08:32 AM
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It looks like most of the responses are geared towards 35pontiac racing his car. I didn't see that in his opening thread. While I do see that 2x2 tubing would be the optimum, I can't see that it's needed for a street driven car - it sure isn't for the OEM's. In my case with a full fendered Model A roadster, it's literally an impossibility with the narrow frame and the splash shields. My fix for that is a 1/2" framework sandwiched between two pieces of 16ga and some huge washers on the underside for the seat and belt bolts. I chose that design to replace the totally inadequate soft, draw quality steel Brookville floorboards and to improve the seatbelt mounting points. The floorboards are not riveted in as Brookville/Ford originally designed but bolted in place with many .250 grade 8 bolts/nuts/washers. But of course, I'm not racing NHRA - but stoplight Grand Prix's.....ya never know

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Old 09-14-2009, 12:59 PM
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Here's what I've decided after all the responses plus other research...

For the seat mounts, I'd like to run 1.5" square tube (.120" wall) across the front and rear of the seats as shown. They will run just under the floor pans, on top of the x-member, and bolt to that as well as the underside of the frame channel. Since the crossmember will be running on top of the frame, I will have to notch (miter or whatever you want to call it) the tube and bring it down to the underside of the frame channel at the ends. At the ends, I will run flat plate to allow 2 bolts to run from the top of the sill, through the wood into the frame. The original steel floorpans will remain in the rear, with the bolts running through the floors, into the crossmembers. The original rear wood crossmember will remain, as it is still solid and is mortised with the sill.

The front crossmember will tie into the front floor pans by means of the 3/4" square (.083 wall). The 3/4 tube will run in the same grooves as the old wood "foot boards." One piece will span the width of the floor in front of the shifter and behind the e-brake. The others will just run across the old grooves as support for the new foot boards, which will be 18 ga sheet with a couple of ribs rolled in. The sheet will be rosette welded to the 3/4. The 3/4 along the sills will be tied into the sills by means of welded tabs running to body bolts.

So here are my questions on some of the details...

1. Should the seats bolt straight through the square tube or through flat brackets welded to the tube? I'm thinking gusseted flat makes more sense. 1/8? 3/16?
2. How should the tabs work from the 3/4 to the sill? The tube will sit recessed below the top of the sill so the tops are flush. Maybe run 1/8 plate, welded to the top of the tube to the body bolts? Should I add another body bolt halfway between the 2 existing ones?
3. How far onto the sill (past the edge of the 3/4 tube) should I run the foot board steel? Kirk brought up the point that moisture will collect in between , so should they end at the joint with the sill?
4. Should the 3/4 tube at the front be bolted to the x member in the middle? Or leave it only attached to the body and free of the mountings to the frame?
5. How should I make the master cylinder accessible? Right now, the left foot board just unscrews and I can get to it from there. I would like to make it hinged or at least screwed so that I can get to the master. Thoughts? This is really one of my biggest holdups for how to make it accessible, but still strong...
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Old 09-14-2009, 01:04 PM
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Quote:
Originally Posted by Irelands child
It looks like most of the responses are geared towards 35pontiac racing his car. I didn't see that in his opening thread.
I am definitely not racing the car, but I wanted to know the racing standards just to compare. It may see the track once, just to see what it can do, but that's about it. I just want it to be as safe as possible while still being practical.

You'll notice that with the seat crossmember mounting to the frame and the body, that will hopefully tie everything together well. Plus, there are a total of 14 body bolts on the original, plus what I am adding, it will take quite a bit to separate the body and frame.
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Old 09-16-2009, 11:47 AM
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I've been in 6 crashes over the years all with seat belts. The first back in 1960 54 Olds vs 60 Ford . Both cars totaled. My Olds floor behind the seat where the seat belts were mounted buckeled about a foot and probably saved me from real seaious injury. Seat belts weren't cool back then and mounting was pretty flimsy at best. The whole floor behind th front seat caved up as I had mounted the belts on a 1/4 x 3 steel plate under the floor.

Later ones were mounted on tubing. In each case the tubing bent and stretched. That's a lot of force. I got heavily bruised each time but I'm still here to tell about it. I've never seen or heard about body movement. I would guess that fiberglass body like my Willys will shatter and cave in pretty easily. I still would rather be inside than on the pavement. You would have to have the body poorly mounted to have movement I think.

I wouldn't mount belts in wood unless it was heavily braced. Use only thru bolts and big thick washers. They used to make railroad bridges out of wood so it can't be all bad. Even if it does break or give it will absorb a considerable amount of energy so it will help some. At least mount the lap belt to the frame some way.
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