1979 RX-7 first gen
Not sure seat belts are working properly?
Are they supposed to lock if pulled suddenly? Mine will not lock with any kind of pull, jerk etc.
Do they only lock in a crash with certain G load or are mine defective?

 

You may need to take the mechanism apart to inspect and clean it. Maybe light lube as well.

It should lock up on hard braking or even leaning forward quickly.

 

 

I've noticed this too with the belts on my '80. Without any accurate terms... I think the SA's only lock up under hard braking with the "decel rocker" that shifts forward and locks the cartridge. If you look at the actual mechanism (you'd have to remove the behind seat plates) on an SA and an FB, you will notice the FB's have an additional piece attached to the side of the belt mechanism frame. I'm guessing this is what allows them to lock when you pull it quickly, although I have never investigated more. I might be able to throw a couple photos up later if you'd be interested.

 

I am looking for complete replacement for seat belts.

 

I've had mine apart and you are right, the mechanism inside that locks the seatbelt in my 78, can only be activated under braking as the mechanism has to slide forward to lock.
I was worried that mine weren't working either, until I opened up the seat belt

 

There is a...um...pin thing inside the seatbelt retractor that swings and locks up the belt if it's not level. Take the retractor off and tilt it 90 degrees. If it doesn't lock up the belt, it's not working.