Technical 3 point seat belts in a '31 Sports Coupe.

Yep, I took your drawing idea and messed about with it a bit.

 

One can only do so much to achieve that goal but anchoring into the subframe and or the frame too, you can't get stronger than that...

 

Maybe I'll leave the over acessorised non matching straps in place for a while

 

...... @282doorUK lets see the whole shebang, Sport Coupes are awesome...is it a hopped up banger?...Av8,,,must be if you want to be strapped in......Searched...they always say search is your best friend...

https://www.jalopyjournal.com/forum/threads/31-sports-coupe-making-it-mine.1306036/

 

This is from my hard copy of the build guidelines in my state:

 

Thanks, that's the info I was hoping for, and I reckon that's easily doable.

 

Interesting subject. I have no experience with a Model A, but have installed a few 3 point belt systems in older pickup cabs, which have similar closeness. My opinion is that maybe those seat belts in that old truck cab might not protect me in a major crash, but any help has to be better then none. Let me put this into perspective. I was in a 50 Dodge pickup (on a modern chassis) and was involved in a head on crash @ 30 mph. The truck did have a lap belt, but I didn't wear it (was not wearing it in the crash) because I was concerned the lap belt would put my head in the middle of the windshield (I would have been correct). I was lucky enough to have survived pretty much uninjured, but I have a persistent pain in my neck to remind me of the event. Everything I've built since then has had 3 point belts, and has developed my opinion concerning 3 point seat belts in older vehicles. That 3 point belt might not save me in every crash, but any help has to be better then no help.

As far as a Model A is concerned, my 1st thought was: Does your Model A still have the wood structure, or has the wood been replaced with metal?

If it still has the wood structure, what good will it be to try to be held in the seat and have the car body clasp around you as the pull of the seat belts rip the body structure apart? The design of the 3 point seat belts relies on the use of the automobile body structure (or the seat frame structure) to hold the person in the seat. The belt anchor points rely on that body structure to distribute the persons body weight to as much of that structure as is required. A wood body structure does not have that level of strength.

If the wood has been replaced with a metal structure, the body MAY already have most of the strength required for the seat belts to do the job. Short of a 4 point roll cage, that metal body structure might do the job. The trick here is to connect a couple of those metal structures together for extra strength, which could also provide the top anchor point on the 3 point belt system.

Again, I have no concept of a Model A metal body structure, but the old truck cab metal structure (from the late 30s Dodge trucks on) has a metal frame work around the doors. That metal is fully boxed everyplace around the door frame except from the floor to the door latch on the rear end of the door. That metal structure also wraps around the rear window and is often tied to the frame work around both doors. That frame work may also be attached to the bottom at the rear of the cab. In the case of the late 30s Dodge truck cab, that structure that connects the door frame to the rear window frame was a bit on the weak side. A curved piece of 1/4" x 1.5" bar stock tacked to the back side of the door frame and to the back side of the rear window frame, in addition to what the factory (or the wood replacement structure) provided sure solved that problem. A 3 window cab provides a lot of room to place that 1/4" bar stock so it can be at the correct height for that upper belt anchor point, and with a holed drilled through the bar at the correct position to place the belt in its desired location around the curve, solves a lot of that belt position issue. If that hole was drilled large enough for the 7/16" fine thread seat belt anchor bolts to pass through, and then the proper size nut was welded to the back side of the curved 1/4" bar. The idea with all that is that in a frontal crash, the seat belt will pull forward. If it moves, I want it to bring as much of the rest of the cab as it can with it, if it pulls the entire rear corner of the cab with it, that is the most protection the structure can provide. With the set up above, the belt anchor point would have to first straighten the 1/4" bar stock, or pull it past the rear window frame, or past the door frame, (so reinforce those attaching points accordingly) or it would have to bring everything forward with it. If it pulls that much cab structure, you would not have stood a chance with out that belt at least providing that much protection. Its all a matter of perspective.

A 5 window cab has better support between the rear windows, the corner windows, and the door frames then a 3 window has, but you loose the option of choosing the best location for mounting that upper seat bely anchor. With a 5 window, the odds are the rear door bracing is the only option that puts the belt even close to where it needs to be. Nearly every 5 window factory cab structure I've seen has a mostly enclosed tube structure around the doors and the quarter window. Often the lower section, below the door latch is open, and in some cases, the top of the door frame may be open. With a little bit of reinforcing, that area between the rear door frame and the quarter window probably has enough strength to provide an upper seat belt anchor point. That additional reinforcing can also be used as a method of attaching the the belt to the door post.

Again, the concept is to make it so if that belt anchor point pulls forward, it has to pull as much of the side of the car with it as possible, and if it does that, you would not have stood a chance with out the seat belt providing that much protection. Perspective man.

I'm not going to pretend I know what the rear door frame nor the quarter window structure looks like on your ride. All I can do is show you pictures of what my 49 Dodge truck cab looks like, and what I did. It might give you an idea of what might work on your ride. Keep in mind, every time you add a curve or bend to flat sheet metal, you multiply its strength toward bending against the bend or curve, box those curves or bends in to a form a tube shape really increases its resistance to bending. That is the reason most body panels on vehicles are not flat, but have at least some curves. Body lines not only add an appealing look, but they also add a lot of strength to the body.
Pic 1) Lets look at my 49 cab door post from the outside. This curved area extends from the top of the cab to the bottom along the rear edge of the door, one would not expect this many curves and bends to fold up very easily in just this form alone.
Pic 2) The outside of the cab, from the rear quarter window angle. Even more curves = more strength.
Pic 3) From the inside, rear quarter window and door post. More curves, 3 separate pieces, all welded together forming a tube, enclosed completely from the top rain gutter to below the door latch, then it was 3 sides with the rear edge open.
Pic 4) This is the inside view of the door post "tube." The hole drilled is a 5/8" hole. The top seat belt anchor bolt is a 7/16" fine thread bolt and it passes easily through this hole. This hole is drilled at the best possible location for the upper seat belt anchor bolt and the hole is centered on the door post width. You will also notice that the metal the hole is drilled through is pretty thick, it is actually double wall, two of the three pieces that form this area overlapped in this area. The areas around the hole above and below the center hole have been ground clean, that is why they appear different. I will be welding those holes closed shortly.
Pic 5) The "flat" area on the door post facing the inside of the cab on my truck is about 1 3/8" wide. In my stash of metal I found a piece of 1.25" structural channel iron (1/4" thick flat stock of the correct width would have also worked). I cut the length so I could slide it up into the door frame tube from the bottom. and make it long enough I could clamp both the top end and the bottom end to the door post tube. The channel iron was clamped into place (flat side against the inner flat side) when the seat belt anchor 5/8" hole was drilled, and that hole was drilled through everything at the same time. Once the hole was drilled in the channel, and the hole was deburred, I welded a 7/16" fine thread nut to the channel side of the channel iron. Drilling that hole through everything at the same time, when everything is clamped into place, assures the holes will match up. With the reinforcement channel slid back into place, the seat belt anchor bolt was screwed through the holes and into the welded nut, and it was tightened up to assure it fit correctly, then the channel was removed from the door post. Then I marked the door post for the weld through holes. I put two 3/8" holes through the door post above the seat belt anchor and two 3/8" holes below the seat belt anchor bolt. With the now 5 holes in the door post drilled, the channel was reinstalled, bolted and clamped into place, and the four weld holes were marked onto the channel, and the channel was removed.
Pic 5) The 4 places marked for the weld holes on the channel were ground to shiny metal, and the area around the weld holes on the door post were also cleaned to shiny metal. The channel was then reinstalled into the door post. First it was bolted into position, then the ends were clamped, then the 4 weld holes were welded closed. Once welded, the seat belt anchor bolt easily is removed and installed and with a flat washer, tightens against the door post. This seat belt bolt has a long enough shoulder for the belt anchor to pivot freely on the door post with the bolt tight.
Pic 6) This is what the seat belt anchor bolt hole looks like on the finished truck, without the seat belt in the way. You have to look for it pretty hard, the hole is at about the center height of the corner window, on the door post. For it to move in a crash, it has to pull all of this with it. Ideally, it would sit back another 2" - 3", but the corner window glass isn't much support, and the seat back wouldn't take the stress of a seat belt at all. In its current position, the belt anchor is slightly behind the seat back, and about 6" farther towards the outside. In a hard angle crash, its possible the belt could slip off the shoulder, but its still much better odds then not having a belt there at all.

 

https://www.jalopyjournal.com/forum...s-in-a-31-sports-coupe.1306194/#post-15066431

...Did you by chance see this post...there's no wood in this structure to be installed and anchored to the frame/sub channels, it is specifically for the belts...

 

I have been pondering this over and over in my head for quite some time myself.

Building my 31' tudor every step in the body and floor integrity has been a major concern. Working on cars everyday that are wrecked keeps that side of car building in the back of your mind.

I do the frame and body structure side of wreck repair along with the custom building and fab side too so I'm always repairing something that's been hard hit usually then maybe the next day doing fab work on a hot rod so I'm always looking at a better way to build a mouse trap and making it safe.

My model A floor structure is over built and hopefully made to drive the engine and Trans under the car incase of a head-on. Some give me crap about it but that's OK, once it's on the road and full of my grandkids I know I'll breathe a little easier knowing it's as safe as I can make it.

Sooo I'm planing on building a channel above the rear window just behind the B-pillar and mounting the anchor to that. Have to get a little further along to see how good it will work. The upper outer wood has been replaced with 1" heavy wall square tube.

..

 

Hey @lostone , just found and looked through your frame construction threads. Very impressive. I have saved them so I can read them in full, and for future reference. Excellent workmanship. No such thing as overkill....

 

Can't think why I never thought of it before, but I have a Camper van with a German made convertible bed/seat installed, which has seat belts for when it's in the seating position.

Hidden under the unit is the frame that the seat belts are fixed to, it's just two parallel rectangular tubes bolted to the floor with two uprights and a cross bar and two angled rear supports all 1:1/2" x 3/4".

It does have retractable belts, which makes things much easier, and it must have passed EU type approval so that's good enough for me.

Here's my updated design which apart from sloping backwards a bit is almost the same thing, except I've added cross ways triangulation braces.

It will be fixed to the floor and sub frame not the main frame.

 

Excuse the OT pics of the Camper van seat belts but they're relevant for info.

 

Seasons greetings folks, and it just about time for a yearly update on this project.

Hopefully you should be able to work it out from the pics.

Morticing the top rail into the uprights is much better than tack welding as it makes things a whole lot easier for trial assembly.

There will be a fair bit of leverage on the uprights above the rear brace bolt, but hopefully the 3mm wall will take it, I may decide to move it up through the parcel tray to ease that.

Not too sure about the head rests, they might not stay but with them in place it's very hard to get my head to contact any hard bits, which will be well padded anyway.

 

I built something similar on my coupe,
I didn't know about this thread and yet it is similar.
It is braced against each other under the parcel shelf and supported at the front and screwed into the frame with high-strength screws, there are also reinforcement plates in the frame channel, additionally screwed to the flange of the panels.

 

That looks like it'll work fine Deutscher, I'd like to see how you fixed the inner belt bolts to the floor, I have to tackle that bit next.

BTW great belt colour choice there

 

I actually didn't take any pictures of this, just of the planning.
I'm using the support behind the seat recess.
There's a reinforcement from one side to the other and screwed on the outside, and in the middle the inner straps are screwed to a belt plate.
I then have to lead the straps through the frame of the seat.

 

Thanks, I'll be using the rearward dicky seat support in the same way, which should get the belt angle closer to what's recommended by the makers.

 

As I recall on my 32 Sport Coupe, I'm able to get a hand behind the upper 'B' post where it meets the top fabric to get a nut & washer on a fastener similar to the posting #3 by 282doorUK

 

@282doorUK

Thanks for posting all of this. What CAD program did you use?

 

Hope you found it useful Sarge, I used Sketchup free version.

https://www.sketchup.com/en/plans-and-pricing/sketchup-free

 

Got a bit more done.



Parcel shelf wood held up with a couple of small brackets, and wood seat spacers fitted to allow room for the belts move, those rough bits would snag the belts.



Fitted plastic bits to cover rough bits, it'll be hidden by parcel shelf upholstery.



I've also moved the rear braces up to above the parcel tray to lessen the leverage, made a flanged plugs that were plug welded inside the tube .



Spreader plates underneath, glass fibre splash aprons make access nice and easy, holes will be covered with sheet ally screwed on.



Rear brace fixings, made a bit of a slip up here as raising the brace up meant the end moved further forward, trimming the wood back a bit fixed that, didn't want to but don't think it matters too much.



Just the centre belt fixings to sort out next.



Made a hole in the seat for the centre belts to pass through, then glued the carpet back and used a bit of rubber hose to trim it with, it'll get a longer bit when I find one.







That's it for now folks.

 

Id only do a three point in an a with a cage. Especially on a soft roof one

 

Your face, your dash, I do hope they never meet..

Granted the Model A is a high car, but hundreds of thousands of UK and European sports cars and convertibles have 3 point belts fitted (it's been the law since 1965) mostly without any roll over protection whatsoever.
I reckon the number of them that have rolled over is tiny in comparison.

Lap belts have been illegal here since 1981.

 

Rollover is the least of the worries. Show me a single spot on the b pillar of a model a that is strong enough to withstand the force of 150+ lbs being yanked on it at speed. All of those euro sports cars since 1965 were engineered for shoulder belts. Take a depression era car that was engineered before seat belts were a thought and used wood as part of the structure. Then revert to my previous comment.

 

The entire thread is about retrofitting anchor point structures to work around that.

 

Good work, it will do its job, we all don't want to have frontal collisions on a country road with our vehicles, that would be a lottery even in a modern car with all its safety systems, here is just an extract from the European approval regulation for seat belts, which is for modern vehicles.

5.3.3. The load must be applied as quickly as possible. The anchorages
must withstand the specified load for at least 0.2 seconds.
5.4.1. Testing when using three-point seat belts that have a retractor and
deflection fitting on the upper anchorage
5.4.1.1. A pulley or deflection for the cable or strap that is suitable for transmitting the test
force from the pulling device, or the pulley or deflection supplied by the manufacturer is attached to the upper anchorage.
5.4.1.2. A test force of 1 350 daN ± 20 daN must be applied to a traction device (see Annex IV, Figure 2) by means of ropes or straps constituting the shoulder part of the safety belt.
5.4.1.3. At the same time, a traction force of 1 350 daN ± 20 daN must be applied to a traction device (see Annex IV, Figure 1) connected to the two lower anchorages. For lap belts, this force must be doubled.
1350 daN is 1350kg
Just so you can see how long and how much force is applied.
Best wishes, Harald

 

Exactly, thank you.

 

Perfect thank you, I was just trying to write a reply to explain all that.

When a 'three point' seat belt has retractor unit fixed to the floor it becomes a four point system, the shoulder and buckle slip fittings act as snatch blocks, so the forces even out to all four mounting points.

Not only are the forces doubled with only a lap belt, they are mostly taken by the soft belly first before hitting the lower spine. With a three point belt the load is taken almost entirely by the skeleton.

 

That is very useful information, thanks. Could you perhaps post the two illustrations it refers to as well?

Is the test force to be applied horizontally? I ask because the test force is a bit over half the typical belt tensile rating of around 22500N, so perhaps it takes geometrical factors into account?

 

There you go,
but as I wrote, this is for the registration of new vehicles.
For classic cars this is not checked, only inspected.
Greetings Harald