Any lap belt should work. All that matters is what style you like. I will be getting some 60's belts, with the big chrome buckles, for my 56.

 

Julianos is a good source. Got mine from there reasonable and quick delivery

Bill

 

eeeeekkkkk guys, seat belt underfloor washers should be 3 inches, DO NOT use anything smaller. Federal guidlines require 3 INCHES BEHIND SHEET METAL FOR PROPER PULL.

 

Let's consider the context. Federal guidelines doesn't recommend lap belts, but that is what we are talking about. I think that the cab floor in a '54 F100 squeezed between a couple of 1-1/4" OD 1/8" thick case hardened steel washers will do the job.

Each person has to ask themselves how much is enough. And they should base that on where they are driving, at what speeds, and how much. The driver with three air bags aimed at his head will tell anyone with less that they are at grave risk.

 

Sorry, since I design and sell the stuff I guess I get a little on the overboard, overbuilt side. Of course we have to go by certian rules (because we are reselling the item) that are sometimes silly or just plan impossible, when dealing with a truck that is now 50 years old. Most people building thier own truck are a lot more safety minded that ever these days and I have seen some wonderful installations. Didn't mean to overstep.

 

Sy:

You certainly did not over step. It is this kind of dialogue that makes this venue so useful and interesting.

Thanks,

 

Sy
I will buy the proper anchor points when it come time to install them.
My face may be ugly to some, but I like it, (Except at O'dark:thirty in the morning).

 

You all know I love controversy so I might as well jump right in. 1 1/4 fender washers is the wrong answer!!!! I just completed a Defensive Drivers Course from the National Highway Safety Council yada yada yesterday.

I'll get the specific statistics tomorrow for the resident physics experts to crunch. The force on the belt mounting points when an Effie slams a stationary object is just unreal. I'll get the specifics. It's many thousands of pounds for a 200 pound driver and a 50 mph collision.

 

Well this is educational and I like it!!

I'll be interested to hear what the Physics major has to say. Personally, I like to overbuild on safety, so I welded 4"x5" plates of 14 guage steel, top and bottom. at 90 degrees and then welded a heavy washer and nut to that on the bottom side.

In the upper corners of the cab I installed 1/4" plate after welding a nut to the back side.

I didn't do the math, just intuited it I suppose!

"53Merc
M100

 

I am sure the force excerted on the bolt at the floor mounting point is unreal 1 1/4 just doest seem big enough. I looked into something at speedway motors and they have a kit that uses a 2 1/2 OD washer. These guys sell all kinds of items including racing equip so I like to think they have an idea of what will work safely.

 

Because they sell all kinds of racing equipment, they use 2/1/2" washers on their four point racing harnesses.

But this thread started as a discussion regarding lap belts on a 54 F100. My Effie has a 4.86 rear end; I'm in high gear at 20 MPH and I top out at 45 MPH. So, I rarely go on the highway. My main concern is staying in front of the steering wheels and pedals. I think the 1-1/4" diameter 1/8" thick case hardened washers will do that for me.

 

Steve

The 1 1/4 washer isn't what is going to fail. You aren't securing enough floorboard sheetmetal. That's the issue.

 

I didn't say that the washer was acting alone to do the job. We are talking about the washer because that was what the original question asked. The job of the washer is to distribute the force load over it's area.

And, it is the radius that get's squared in the area formula. So bigger is better. That's why 53Merc is using 4" X 5" plates. Each of us has to decide how much is enough in our application.

 

OK, according to the NHTSC, here’s what we need. Assuming a 220 pound driver in a 30 mph collision with a stationary object, the force applied to the safety belt is 4,400 pounds. Assuming the force is evenly applied to both anchor points, with a 2 point safety belt, we need each mount point to withstand a 2,200 pound force.

My questions are:

Would it go up by a simple factor of 2 for a 60 mph collision?

Would the numbers go up for a head-on collision rather than colliding with a stationary object.

Does the safety belt webbing stretch absorb some of the energy and reduce the amount of force applied to the mounting point?

I at one time considered attaching to the transmission crossmember. I have re-evaluated that logic now that I have considered the unimaginable force or a cab launch on my waistline.

I don't know what this means in washer diameters.

OK, George, don’t blow us away with 2 pages of equations if you can help it.

 

No. Although the total deceleration required it twice as great, it's going to happen over a longer distance since the truck will likely be crunched up a bit more. The multiplier will be somewhere between 1 and 2 - I'd bet closer to 2.
Depends on what you hit. If you hit another vehicle of the same size (mass) and crunchiness, then both will stop as if they hit a stationary object. If you hit a smaller vehicle, you will likely cause them to reverse course - your deceleration rate goes down, theirs goes up. Hit something bigger that causes you to reverse course and YOU get the bigger deceleration.
Probably, but I'm pretty sure my belly would be squishing a lot more than the belt would be stretching. That's just me, of course. The stretch of the seat belt is way, way down in the noise as far as the estimates we are making here.
Overall safety restraint (seat belt, air bag, etc.) design is driven by keeping the passenger within a safety zone, and keeping other things out of the safety zone. In the unlikely event that the cab wanted to leave the frame, and you were strapped to the frame, you would tend to be pulled through the seat and wall/floor of the cab. I imagine that would not be too good for your health. On the other hand, if the cab stays with the frame, your belts would definitely keep you in the cab - at least as far as the anchor points go.
There are at least four clear failure modes for the belt anchor points - certainly more that are not immediately obvious. The size of the washer is only involved in two of the failure modes I can think of off the top of my head.
If it were me, I'd design for a 5,000 lb load on each lap anchor and a 3,000 lb load on each shoulder anchor. Those are the numbers that the NHTSA uses to test seat belts.

For 5,000 lbs, you are not going to get a failure using a grade 5 or grade 8 bolt, at least 5/16" diameter, in either shear or tension. Standard grade 5 and 8 nuts and washers are designed to handle the same load as the bolt.

As 'fenders pointed out, the weak link is the sheet metal the bolt is attached to and, potentially, any hardware that connects the bolt to the belt material. To know FOR SURE, you'd have to do a series of tests on an actual cab to see what size washer it takes to avoid significant distortion of the sheet metal. Note that you don't need to pull the washer through the sheet metal to have failure. If the sheet metal bends three or four inches without the washer pulling through, you may still hit your head on something do to the distortion.

I've already decided to put in a couple of 6"x6"x1/4" steel plates with a 2"x2"x1/4" square tube welded between them. It's simple to do for me because the cab is off and I'm redoing everything. The square tubing means that you'd have to pull the entire bottom/rear edge of the cab inward to have a failure.

Sometimes I fool myself by underestimating the forces involved in various situations. I think the numbers from various folks in this thread give all of us an idea of what those forces are for seat belts. Everybody will have their own way of dealing with the problem - but at least we all know what we are up against.