Seat Belts in 30 Coupe

[dmaxweb]

First off, sorry for another seat belt thread. I've searched and searched for a clear illustration on the inboard belts.
The inboard belts are bolted to the reinforced cross sill behind the tool pan - so far so good. How are the belts routed through/around the wood seat frame and/or the curved sheet metal at the back of the seat?
Thanks
Don

[DaWizard]

First dmaxweb WELCOME to the VFF!!

It would help greatly if you had pictures of how you mounted the belts cause today my minds eye is blind. If you mounted them as I think you did, it is a simple routing under the back and atop the seat. If you didn't mount them as I thought, those pictures will help greatly.

If this thread pans out like I think it will, it can simply be a1dded to the Seat Belt tech thread, so don't be sorry. This is a young forum and I am sure we haven't covered everything yet in the tech threads, but we are adding daily.

[Mitch]

Did you see this seatbelt technical thread. There are some coupe installs documented.
https://www.vintagefordforum.com/for...lt-information
Feel free to share your belt project, and post it to that tech thread

Welcome to the VFF!!

[dmaxweb]

First dmaxweb WELCOME to the VFF!!

It would help greatly if you had pictures of how you mounted the belts cause today my minds eye is blind. If you mounted them as I think you did, it is a simple routing under the back and atop the seat. If you didn't mount them as I thought, those pictures will help greatly.

If this thread pans out like I think it will, it can simply be a1dded to the Seat Belt tech thread, so don't be sorry. This is a young forum and I am sure we haven't covered everything yet in the tech threads, but we are adding daily.

I've not yet bolted down the center belts. The attached picture shows the proposed mounting location. As you can see without any further modification this necessitates wrapping the belt forward around the wood seat frame and back and up behind the seat cushion. Maybe it's not a problem but this leaves several inches of slack between the mount and the passenger. On the "other board" there are some threads recommending cutting a slot in the curved metal riser for the belts so they have more of a straight shot. I have not been able to find a decent picture of this method or get a response over there. Any help much appreciated.
Thanks

[DaWizard]

Oh, ok, now I understand where you want to bolt them down. On the ones I have seen that is not where they were anchored. The ones I have seen they were bolted down to floor with bracing under the mounts back behind the seat pan which gives a more direct line of pull rather than trying to drag the seat forward with the belt.

[dmaxweb]

Oh, ok, now I understand where you want to bolt them down. On the ones I have seen that is not where they were anchored. The ones I have seen they were bolted down to floor with bracing under the mounts back behind the seat pan which gives a more direct line of pull rather than trying to drag the seat forward with the belt.

I assume that installation required cutting a slot for the belts in the metal riser.
I saw the cross sill mount on Vince Falter's page (http://www.fordgarage.com/pages/seatbelts.htm) but it does not show the final belt routing.

[Mitch]

If that install was by Vince, I don't see him cutting anything up. The belt was probably ran up and around the seat cushion.

[Kevin in NJ]

A mistake that can be made is to allow the seat belts to wrap around the seat cushions.

You MUST have a straight line from the mount point to around you waist. The reason is the belt will pull a substantial distance (that dash is really close to you in the A) before it gets tight. The belt will then stretch some more cause that is what it is supposed to do. This will also allow your body to build up inertia and cause substantially more force on your fasteners. Think over a thousand pounds.

For my cabriolet I found to get a straight shot for the middle I needed to cut a hole in the curved seat panel. I lined the hole with slotted brake line welded on for smooth surface. The bolts also need to be in shear, as close to 90 degrees from the length as you can get.

My opinion is if you fail to get a straight path to the waist of the person you may not be better off then no seat belts. It is well known that with lap belts improperly set people slide through them in odd ways. No they do not always survive. They must be tight on the hips.

[dmaxweb]

I worked on a rough mock-up this morning for center belts mounting.
- 1/4" steel
- 1/2" grade 8 hardware
- L-Bracket on floor of rumble. 4" wide, 3 3/4" high 2" deep with triangular gussets on ends.
- Flat Backer Plate under floor. 3" wide, 8" long, 2 inner holes for thru bolts to L-Bracket, 2 outer holes to further secure backer plate to rumble floor.
- Seat belt ends bolted to top holes in L-Bracket.
- Slot cut in curved seat riser.

Thoughts?

[Kevin in NJ]

I am going to sound a bit blunt....

If that bracket you show is mounting to the floor pan and sticks up such that the seat belt would pull away from the viewer and not straight up then I would tell you not to bother trying.

That would be a great lever that will instantly tear through the sheet metal.

If you do not mount the seat belt rearward through the metal part of the seat you are not going to be able to make a strong enough mount or route the seat belt straight enough to be of any safety to your body. I would not be surprised if you body could move over 10" in a minor accident impaling you in the steering wheel.

I have a picture of my solution. I am not saying it is correct and I did not calculations. I have a slant window cabriolet and have a wood sill structure. The seat belt would be bolted about 1/3 the way back on the bar. The bar would be mounted under the floor pan. I have distributed the force such that the front the bar has a plate that is screwed in by heavy wood screws all in sheer. The rear is pulling up on the rear metal cross sill. The seat belt is like a 20 or 30 degree angle. So some force is vertical and most is forward.

I figure it will hold for most normal accidents.

Note that you can see the seat frame at one time might have been used with seat belts as it had those square hole cut in it. I fill them in and only the center got recut after I put the springs in to ensure I got the straightest path for the belt.

My side belts are mounted rear ward through the wood. They also have a long straight line putting the bolt in sheer. I also have a large heavy washer to make sure it spreads the force.

[dmaxweb]

I am going to sound a bit blunt....

If that bracket you show is mounting to the floor pan and sticks up such that the seat belt would pull away from the viewer and not straight up then I would tell you not to bother trying.

That would be a great lever that will instantly tear through the sheet metal.

If you do not mount the seat belt rearward through the metal part of the seat you are not going to be able to make a strong enough mount or route the seat belt straight enough to be of any safety to your body. I would not be surprised if you body could move over 10" in a minor accident impaling you in the steering wheel.

I have a picture of my solution. I am not saying it is correct and I did not calculations. I have a slant window cabriolet and have a wood sill structure. The seat belt would be bolted about 1/3 the way back on the bar. The bar would be mounted under the floor pan. I have distributed the force such that the front the bar has a plate that is screwed in by heavy wood screws all in sheer. The rear is pulling up on the rear metal cross sill. The seat belt is like a 20 or 30 degree angle. So some force is vertical and most is forward.

I figure it will hold for most normal accidents.

Note that you can see the seat frame at one time might have been used with seat belts as it had those square hole cut in it. I fill them in and only the center got recut after I put the springs in to ensure I got the straightest path for the belt.

My side belts are mounted rear ward through the wood. They also have a long straight line putting the bolt in sheer. I also have a large heavy washer to make sure it spreads the force.

Kevin,
Thanks for your input.
I looked at your website and have "plan B" for my coupe. A 4" wide steel channel mounted fore and aft under the center of the rumble floor. The ends would be bolted to the channel in the cross sills in front of and behind the rumble floor with 1-1/2" wide flat bar as a spacer in the cross sill channels.
The picture illustrates what I'm trying to describe using some scrap I have laying around. The channel would be steel (not aluminum as in the picture) and obviously longer. The cross pieces (spacers in cross sill channel) would be thicker and longer. The center seat belts would be bolted through the rumble floor into the fore and aft channel. This allows me to place the seat belt mounting bolt as far back as needed to have a straight line to the seat.

Thoughts?

Thanks!

[Kevin in NJ]

My opinion is the 4" wide channel may be too wide if the metal is too thin.

I do not know the correct mechanical engineering to determine the correct thickness metal. I made my fore aft piece out of 1/2" thick bar. My reason was to have enough meat for the belt attachment bolt plus enough strength to handle the forces of the bolt being pulled forward.

Think metal heavy enough to pick up the car in the direction of the belt. If you feel confident you could pick up the whole car by the seat belt then you are probably pretty good.

Some thoughts of how I arrive at my decisions. I have looked at a bunch of cars in the junk yard to see how they did belt mount points. They were always in thicker sheetmetal in a tight U section and in sheer. Not as beefy as I would have expected, but the strength would come from the channels they created.

As I say most of what I say is my opinion and gut feeling and not based on calculations.
So take my advice at that value. I wish I could give you a better answer, but my knowledge on materials is not such that I could give a proper answer.
My best advice is think that you want to be able to pick up the whole car in the direction the belt would be in an accident.

[dmaxweb]

My opinion is the 4" wide channel may be too wide if the metal is too thin.

I do not know the correct mechanical engineering to determine the correct thickness metal. I made my fore aft piece out of 1/2" thick bar. My reason was to have enough meat for the belt attachment bolt plus enough strength to handle the forces of the bolt being pulled forward.

Think metal heavy enough to pick up the car in the direction of the belt. If you feel confident you could pick up the whole car by the seat belt then you are probably pretty good.

Some thoughts of how I arrive at my decisions. I have looked at a bunch of cars in the junk yard to see how they did belt mount points. They were always in thicker sheetmetal in a tight U section and in sheer. Not as beefy as I would have expected, but the strength would come from the channels they created.

As I say most of what I say is my opinion and gut feeling and not based on calculations.
So take my advice at that value. I wish I could give you a better answer, but my knowledge on materials is not such that I could give a proper answer.
My best advice is think that you want to be able to pick up the whole car in the direction the belt would be in an accident.

The channel steel would definitely be thicker than the aluminum shown in the mock-up picture. I was thinking at least 1/4". With the channel bolted to the sill channels at each end and the additional (minimal) strength from the bolt(s) through the rumble floor for the belt mount. Did you mount both belts to a single bolt? The reason I was thinking 4" wide was to use a separate bolt for each anchor. Perhaps not necessary.

Again, I appreciate your input.

I agree with you that others reading this should not take it as the "correct way", the "only way", or the "safest way". There are far too many variables not the least of which we are dealing with 90 year old vehicles never designed for seat belts.

[dmaxweb]

After checking around, that size channel steel is not readily available. So, I've simplified the design as pictured in wood mock-up.

1 4" x 1/2" flat bar 22" long
2 1-1/2" x 3/4" flat bars 12" long

Four red dots in picture are holes for 9/16" bolts through body cross channels.
Hole(s) will be drilled in flat bar through rumble floor for belt mounting at location to be determined.

[dmaxweb]

A mistake that can be made is to allow the seat belts to wrap around the seat cushions.

You MUST have a straight line from the mount point to around you waist. The reason is the belt will pull a substantial distance (that dash is really close to you in the A) before it gets tight. The belt will then stretch some more cause that is what it is supposed to do. This will also allow your body to build up inertia and cause substantially more force on your fasteners. Think over a thousand pounds.

For my cabriolet I found to get a straight shot for the middle I needed to cut a hole in the curved seat panel. I lined the hole with slotted brake line welded on for smooth surface. The bolts also need to be in shear, as close to 90 degrees from the length as you can get.

My opinion is if you fail to get a straight path to the waist of the person you may not be better off then no seat belts. It is well known that with lap belts improperly set people slide through them in odd ways. No they do not always survive. They must be tight on the hips.

Couple of questions for you.
What size slot did you cut in the curved seat panel?
Did you attach both inboard belts to a single bolt or individual bolts?
Thanks

[Bill Z]

Here’s how I mounted seatbelts in my ‘30 Coupe. I fabricated a bracket using 3” wide X 3/16 steel with 1” X 3/16 stiffeners welded to the sides, then mounted under the floor to the body cross members. Nuts were also welded underneath to attach the middle belts. The side belts are mounted to the sub rails using welded nut plates slid under the sub rails and over the splash aprons from the rear wheel wells and pop-riveted in place. My belts are mounted a little farther back than usual since I moved my seat back 4 1/2”, requiring me to also modify the package shelf, which is now only about 2” deep. I’m 6’ 3”, and it’s the only way I could fit in this car.

Bill Z

[dmaxweb]

Here’s how I mounted seatbelts in my ‘30 Coupe. I fabricated a bracket using 3” wide X 3/16 steel with 1” X 3/16 stiffeners welded to the sides, then mounted under the floor to the body cross members. Nuts were also welded underneath to attach the middle belts. The side belts are mounted to the sub rails using welded nut plates slid under the sub rails and over the splash aprons from the rear wheel wells and pop-riveted in place. My belts are mounted a little farther back than usual since I moved my seat back 4 1/2”, requiring me to also modify the package shelf, which is now only about 2” deep. I’m 6’ 3”, and it’s the only way I could fit in this car.

Bill Z

Thanks Bill, that gives me a couple ideas. Do you have the dimensions of the opening that you cut in the curved sheet metal under the front seat for the center belts pass thru?

[Kevin in NJ]

Couple of questions for you.
What size slot did you cut in the curved seat panel?
Did you attach both inboard belts to a single bolt or individual bolts?
Thanks

The hole size is eyeballed big enough to allow the belt through with no restrictions.

I only have one bolt.

[Bill Z]

The slot dimensions are approximately 1 1/2” X 4-6”. As Kevin in NJ said, big enough for no restrictions. I protected the belts from abrasions with some vinyl edging secured around the openings with polyurethane glue.
Bill Z

[carolinamudwalker]

Maybe it is just me but lap belts mean you are going to eat the steering wheel and the passenger is going to have her face all over the windshield. I urge you to check out the 3 point belts as Mitch suggested, do a search.

[dmaxweb]

The slot dimensions are approximately 1 1/2” X 4-6”. As Kevin in NJ said, big enough for no restrictions. I protected the belts from abrasions with some vinyl edging secured around the openings with polyurethane glue.
Bill Z

Looks great!
Is the vinyl edge trim from McMaster Carr? Do you happen to know the part number?
Thanks!

[Mitch]

Looks great!
Is the vinyl edge trim from McMaster Carr? Do you happen to know the part number?
Thanks!

It does look good

[Bill Z]

Looks great!
Is the vinyl edge trim from McMaster Carr? Do you happen to know the part number?
Thanks!

Actually, I ordered the trim from Amazon. KX black vinyl 1/8” edge trim. $10.99 for a 10 foot roll.

Bill Z

[pooch]

A seat belt bolt should be grade 5 only.
Seat belt bolts are standardised as 7/16 UNF 20 and grade 5.

They have shallow domed heads which were designed for a 165 mm (human head size) to roll around inside a vehicle and not get cut.

A grade 5 bolt will bend in shear whereas a grade 8 will fracture in shear.

[dmaxweb]

Here’s how I mounted seatbelts in my ‘30 Coupe. I fabricated a bracket using 3” wide X 3/16 steel with 1” X 3/16 stiffeners welded to the sides, then mounted under the floor to the body cross members. Nuts were also welded underneath to attach the middle belts. The side belts are mounted to the sub rails using welded nut plates slid under the sub rails and over the splash aprons from the rear wheel wells and pop-riveted in place. My belts are mounted a little farther back than usual since I moved my seat back 4 1/2”, requiring me to also modify the package shelf, which is now only about 2” deep. I’m 6’ 3”, and it’s the only way I could fit in this car.

Bill Z

Maybe I'm missing something. How were you able to slide the side belt backer plates under the sub rails and then hold them to pop-rivet in place? The opening from rear wheel wells is way to small to reach into.

Can this area be accessed by removing the rumble seat floor pan?