Post
by Steve Simmons » Thu May 02, 2019 2:22 pm
Hi Steve,
There is a bit of controversy about how to best install seat belts in cars this old. Some say lap belts, some say shoulder belts, some say no belts. The problem is that the car wasn't designed for them, so no matter how you install belts, you will be making compromises.
One big issue is the fact that the body and frame are separate, so in a serious enough collision the body could potentially break away and shift in relation to the frame. If this happens and you have bolted the seat belts to the frame, then one of two things can happen. The body could move rearward which would loosen your belt and allow you to be thrown about or slide under. Or, the body could move forward and since the seat is mounted to the body, the seat could move several inches while the belt stays where it is and result is serious abdominal injury.
On the other hand you could mount the belts to the body, but then you run the risk of the bolts tearing out of the wood, which is obviously no better. In a collision this serious belts may not help you anyway, but may as well take the best precautions possible.
Another scenario worth considering is a roll-over. In this case some people say a shoulder belt will kill you since you won't be able to duck. Others say you'll never be able to duck against such violent forces anyway. Personally I feel that being locked upright in a roll-over would be far worse than being flung against the windscreen due to lack of shoulder belts. The other issue with shoulder belts is the mounting angles. The only place to mount them is far below the shoulder, which is proven to be a bad idea. In a moderate collision, serious shoulder and/or spinal injury can occur because the belt will pull violently downward. But in a minor collision a shoulder belt can certainly prevent serious injury, namely forehead to windscreen, chest to solid steering column, and in the case of your passenger, forehead to wiper motor.
My personal preference is for lap belts only. My mounting method is to attach the outer belts to the frame behind the seats. The inner belts are mounted to the metal gearbox tunnel with large curved fender washers underneath. The logic in my mind is... should the body move, one side will remain fixed (outer belt) and the other side will move at least partially with the body since the tunnel is partially attached to it. So if the belt tightens or loosens as the body moves, it should only do so 50% of what it would otherwise have if both sides were bolted to the frame. And if the tunnel does tear away then at least the initial impact will be absorbed before the belts begin to loosen.
Obviously the idea is to never get into a collision of ANY kind in these cars, especially against the average modern vehicle. But even if there were no danger of an accident, I would still run lap belts simply because they offer far better control of the car, especially on bumpy roads. I used to expend a lot of energy holding myself in place but once I installed lap belts, all of my energy and attention went toward driving the car.
Hope this helps.
