Seat belt reconditioning

[TZombek]

Has anyone worked with 40+ year old seat belts that are kinda stiff and don't slide through the adjusters properly?

Ted

[steve shea]

If washed in mild soap and water and conditioned with olive or vegetable oil they should soften for cosmetic purpose. The SAFE shelf life of even modern webbing such as dyneema is only about five years. I've got original Repa web on my euro 73S and I'm pretty sure they would fail in a catastrophic wreck but I'm not planning on finding out. I was surprised to find out about the degredation to webbing stored even in a cool, dark place. I use lots of webbing in other pursuits and regulary change it out. UV and dirt and mild abrasion take a toll.

[NorthernThrux]

Yeah, seat belts are supposed to loose 10% of their stretch resistance per year (for perspective in a 10g crash they can stretch 20%). At 10% per year it's not too long before they'll stretch enough in a crash that you'll hit the steering wheel. Remember that energy absorbing steering columns didn't appear on 911's until the 1974 model year.
That said, when I consulted with http://www.vintageseatbelts.com he said just leave it, as he has on his 40 year old 911. The front of an early car is one giant crumple zone I suppose....

[Kris Clewell]

Yeah, seat belts are supposed to loose 10% of their stretch resistance per year

that would mean I'm going through the windshield? There has to be some sort of threshold where they dont stretch much farther than XYZ.

[RSTarga]

Thats the problem, if they don't stretch, your neck will. In racing helmets and seat belts are dated and have a definite replacement time. You would think the factories would have replacement belts readily available, problem is the liability exposure if the belts are installed incorrectly.

[NorthernThrux]

that would mean I'm going through the windshield? There has to be some sort of threshold where they dont stretch much farther than XYZ.

There is. That's when they tear completely !

And yes you can get new seat belts for cars. They get replaced all the time by insurance companies after crashes, even mild ones. These days most seat belts have pyrotechnic tensioners. The whole unit gets replaced in the event of a crash.

It's pretty trivial to install a belt on our cars. It's probably not entirely stupid to consider using new belts for daily use and keep the originals for show.

Ravi

[Kris Clewell]

Thats the problem, if they don't stretch, your neck will. In racing helmets and seat belts are dated and have a definite replacement time. You would think the factories would have replacement belts readily available, problem is the liability exposure if the belts are installed incorrectly.

My point was more along the lines that if the belt stretches an extra 10% a year my belts now stretch around 4x more than they did stock. If they stretch 20% stock, that means I'm literally stretching what...80-100% of their original length? I'm not great at math, just estimating. I should have paid more attention in school...

I just find it hard to believe... if thats the case I might as well not even wear one. There has to be some sort of curve to this theory. It can't be that linear. There has to be a point where if the car is in good nick they really dont deteriorate much past X. I've been in car accidents in old cars without much of a problem with safety belts. I know a guy that rear ended a fed ex truck in an 83 rabbit gti. he walked away with belt bruises.

[Harvey Weidman]

The have LESS stretch as thay get older, not more. Meaning the belt won't absorb as much of the force when old.
H

[stretch]

Having worked with a few webbing companies over the past 2 years, it is a fact that the 1st thing to go in your 40 year old seat belts in an accident, will be the fittings. Then the stitching, and finally the webbing.

One of the tests performed : An original NOS never opened Repa seat belt. V a 43 year old original used webbing.
The result: The 43 year old sample had only lost 20% of it's original break strength compared to the new sample.

Dave

[Kris Clewell]

The have LESS stretch as thay get older, not more. Meaning the belt won't absorb as much of the force when old.
H

Not sure why I read that backwards. Been a long day. Thats why I was just like....what?