How Seat Belts Work

Ever wonder how seat belts work to save your life in a crash?

Well buckle up! This video takes you through the inner mechanical workings of the seat belt mechanism, its various functions and internal components.

The three point seat belt is common on most modern passenger vehicles. Normally unlocked, seat belts give the user sufficient freedom to move around while riding in a car.

However when the vehicle undergoes heavy braking or collides with another object, the seat belts lock - and in some cases retract, pulling the occupant away from smacking their face on the dashboard causing injury.

The seat belts also sense when a vehicle is accelerating hard, on an incline, as well as stop if pulled out too far, as well as sense quick sharp tugs on the seat belt and lock it in place.

A cam gear inside controls how much seat belt webbing can be extracted without locking. A gravity ball inside a plastic casing senses the incline of the vehicle under acceleration or braking. A centrifugal ratchet engages when the seat belt is tugged on rapidly. Finally a small tooth engages to lock the seat belt when all of the webbing material has been extracted.

The front seats are a bit different, as they come with pretensioners. Working with the SRS airbag system, the pretensioners will wind up any slack in the seat belt webbing during a collision. This will hold the occupant away from hitting the dashboard and prevent injury.

Seat belt pretensioners contain an explosive because it has to react very quickly during the collision. The explosive pushes a piston that's attached to a wire. The wire is reeled around the seat belt retractor, and thus winds up the slack when fired.

The seat belts in this video were removed from a 2001 Toyota Corolla, and completely taken apart and detonated to explain what's inside and how it works.

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Reference material:

[dXXPacmanXXb]

the amount of craftsmanship and complexity in such a seemingly simple part of the car

[chrismalitoterec]

Thanks for your effort making this video

[mikea]

Damn, , just stumbled across this video and ended up watching the whole thing.. You really know your stuff. Good job..

[malcolmx]

Very informative video. Thanks for your educational contributions to the community.

[MaximumJonathanosity]

Where do you get OEM spiders? My dealership doesn't supply them.

[aaronhammerling]

Cheers for the video! Turns out the gravity ball was full of fluff, as the seatbelt was completely locked up. Works like new again!

[IFreakingEatPeople]

Thanks brother I’m working on a new project and this really helped me narrow down what I need to emulate

[kcat]

Thank you for this video. I don't know anything about cars, but your explanation was very clear and easy to follow.

[philcourteney]

Brilliant video! I was looking to find out how it all worked, expected some visual graphics, in a dry and boring presentation, but this is brilliant! Reminds me of AVE but without the swearing! Great job!

[davidespalvieri]

Thanks for this video! That's very clear, funny and synthetic! I could finally manage to find the problem in my seatbelt. The gravity ball might be in a slightly wrong position: this causes the belt to stuck often. How would I fix this problem? Is it dangerous to remove the gravity ball and keep driving until find a replacement?

[nasedo]

The seat belt on my old beater acts up a lot. One day I pulled on it fifty times and it wouldn't extend, so I just drove off without using it. Of course a Highway Patrol spotted me in heavy traffic and pulled me over. I demonstrated that it wasn't working that day....he could have given me a warning or a fix it ticket but he nailed me for the full fine, One Hundred Twelve Bucks! : ( Then they wonder why people hate cops : ( Later I used compressed air and blew out about a pint of sand and gravel from the mechanism. It still doesn't work very well but once I got it extended I used a vise grips to keep it there.


Now that I got that off my chest this was another fascinating video!

[sammorex]

Excellent Job, best video describing this ever! Thanks for sharing your knowledge!

[AOMartialArts]

Way to take one for the team, Toothbrush. Your sacrifice will result in millions of saved lives.
*trumpet taps*
*Burrr bur burr bur

[mianarshed]

Always like to watch your videos. Very comprehensive and informative.

[GraniteInTheFace]

My big fat belly and i appreciate your video

[shreedharanvijaykumar]

Real very informative video. thank you for taking your time to make and upload this video.

[ManojKumar-miqz]

Through this video I got some picture about seat belt ...but didn't understand, I am gonna soon disassemble seat belt and learn .thank q

[HashRL]

i enjoy your videos, an easy and fun way to comprehend function principles of any car component, a big salute from Colombia

[AK-kyou]

Cool, had no idea they were so complex. Thank you

[seshachary]

very educative as ALWAYS . Thank you Regards