Go Back   The Ford Barn > General Discussion > Model A (1928-31)

Sponsored Links (Register now to hide all advertisements)

 
 
Thread Tools Display Modes
Prev Previous Post   Next Post Next
Old 03-04-2016, 07:22 PM   #1
Kevin in NJ
Senior Member
 
Join Date: May 2010
Location: South East NJ
Posts: 3,398
Default Safety Issues with Seat Belt Article in Current MAN.

I just received my Model A News. I came to the article on installing seat belts and feel I must bring up some safety issues.

The physics of a seat belt in an accident is that all the attachment points are pulled along their strongest direction. Bolts are put into shear with wide thick washers to distribute force. You will notice the belts are usually mounted back behind the seat in a long straight line.
So when you design a seat belt mount you have to take all this into consideration. You want as straight a line from the anchor point to where it comes up around your hips.

Take a look at the diagram that was shown in the article. You will see the mount is a couple of soft all thread bolts attached to a thin piece of flat metal. The path of the seat belt winds around the seat cushions. The all thread metal piece is extended well above the mount on the sill rails with almost no extra re-enforcement. Too much room for movement of the soft metal.

In the unfortunate event of a quick stop...
The belt material will pull tight against the cushions allowing the person to slide forward. Then the flat steel and soft all thread will bend. This will further give more length to the belt. The countersunk screws are really bad. Very little contact area so they have no strength. It does not take much to pull them out of soft thin steel.
I have attached a scan of the drawing provided in the article. I have added the path of the belt when tension is pulled on the belt.

While the system is better then nothing, I feel it is not likely to hold against much force. I am really concerned that the countersunk screws might pull out easier then you might expect. I am sure an experienced mechancial engineer would be quick to see these issues.

A better way, but more work, would be to cut a hole in the curved metal piece and run the belt in a more straight path rear ward. Then make a brace on the floor area of the rumble to attach the seat belt mount bracket.

For my cabriolet I had some wood to deal with so the idea is a bit different. I made a piece of 1/2" steel bar that screws to the bottom of the wood cross sill with a bunch of wood screws and under the rear metal cross sill. The forces in an accident will be at an angle with most translated to a forward movement against the heavy wood with some of the force pulling up.
I cut a hole in that curved metal part to allow the seat belt to take the straightest path. The mount point for the belt was put back some in the area where feet go for the rumble passengers.
The side mounts are also put rear ward to make for straight lines. They go into the wood with large thick washers.

Keep in mind seat belt installations in the A are always a compromise. Some kind of seat belt is better then none. I feel what was written in the MAN may not be very good and with the countersunk screw maybe even dangerous.

I hope I have not offended anyone.

Now onto an idea for the rumble seat. The rumble seat is very difficult to make a proper seat belt mount point. There is just no room. So I made a lot of compromises. I have included a picture of what I have done. Heavy 1" square tubing under the sills. Then some tabs slipped up through the rumble riser. It is very tight with little room up the back of the seat bottom. Here is a case where way less then optimum mounting happens. The torque on the bar is not good and the tab might bend. Not much you can do.
Attached Images
File Type: jpg coupeseatbelt.jpg (40.9 KB, 318 views)
File Type: jpg ft_center1.JPG (62.2 KB, 248 views)
File Type: jpg rumble_pan1_txt.jpg (111.6 KB, 239 views)
Kevin in NJ is offline   Reply With Quote
 

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Sponsored Links (Register now to hide all advertisements)


All times are GMT -5. The time now is 10:54 AM.