That sounds reasonable, but more likely I (and the seat) will be moving forwards in a crash as the front of the car crumples in deceleration, so the belt will become tighter...

It doesn't do any good to stay strapped in the seat if the seat doesn't stay attached to the floor.

I'll notify the OEM's as soon as I get a chance.

Actually I think you missed the point, no big deal, its not me in the seat.

Then how about explaining it another way, instead of being snarky?

He already explained it...^^^

All the seats mentioned in this thread are awesome, I needed to find something more affordable for my big block Duster so I bought sport seats off ebay for a total of $200 shipped for the pair, even came with slider brackets which I always bolt straight to the floor for head room.
I think for the money they are great, I'm 6'2 230# so I wish they were a little wider but they're fine and they hold you in place very well if you do any cornering.

And I implied a question, which he (and you) have not answered so I will ask again explicitly:

If the seat and the driver are moving forward, and the belt is not (because it is fastened securely to the body), why does the belt not become tighter?

Just an observation. They do look good in that A body vert

It will become tighter when moving forward as long as it is secured correctly and doesn't rip out of the floor. But if you bounce off a wall or guardrail and end up going backwards it will become real loose. It's also very possible to back it into a wall or object during an incident.

With that said, my Duster has 3" lap belts just bolted to the floor with large washers. I need to decide on a factory shoulder harness or something else. This is my first street only build, I'm use to having a 5-way harness mounted to a roll cage.

True, it only gets tighter going forward... although the frontal impact is most likely, at least on a street car.

I suspect another reason for having the seat and belts attached together is that it's quicker on the assembly line!

Anyhow I think I'm going to buy new shoulder/lap belts, manual adjust, that fit the original mounting points (on the floor and roof). 3" sounds like a good idea, to reduce the loading per unit area on my body...

I have never liked retractors since they eventually get "sticky", and I worry that they may not lock when I need them to. I ran a car off the road once at 55 mph and went through the median ditch, flew up in the air and hit my head fairly hard on the roof. The belt never locked with the vertical acceleration, so fat lot of good it did me for that impact!

Incidentally, is there any value to the old bench seats? The driver's spot is, of course, worn out, but the rest is OK. Maybe they should just go to the dump...

"succintness" is sometimes misinterpreted as "snarkiness". The strongest counterpoint to your stated conclusion has been addressed by others already, ie accidents happen in 3d, and can have have multiple impacts. My main original point, ANYTHING that allows a restraining seatbelt to loosen, has a bad outcome.

And which category do you think that remark belongs to?

Yes, of course if the belt loosens there is a bad outcome! And MY main original point was that I don't want to rely on my homemade brackets to restrain my weight plus that of the seat.

I plan to use "old-school" manually adjustable belts as I mentioned previously. No retractors or other inertial-locking devices. One less thing to worry about loosening.

I had a set of L-Body (Charger or Daytona/Laser) seats in a 67 Dart and they were very comfortable, but probably not easy to find nowadays.

Don't pitch the old seat as guys are looking for them.

I agree, bolt the belts to the original floor mount locations . choice of belt is up to you.

I'm not sure, extreme soft sarcasm or maybe borderline snarky, does it really matter, because I think it made my point loud and clear. If it hurt your feelings, that was not the intent.

Might I point out that if you are concerned about your homemade seat brackets supporting you and the seat with the seat belts attached to the seat, how are you so sure the seat brackets will keep the seat in its proper location in a crash? If the seat moves, belts attached to the floor pan are worthless.

How did you make your seat brackets?
If the seats are attached to the homemade brackets with bolts in the original location on the seat, and the angle brackets are bolted to the floors with at least 2 3/8" diameter grade 8 bolts per side, a 3" diameter washer or 1/8" flat steel plate on the bottom side of the floor pan will keep the seat from moving, provided the floor pan remains intact. Modern day seat mounting brackets are attached to the floors on reinforcing plates that run from door to trans tunnel. 2" x 2" x 1/8" angle is heaver gauge metal the the seat frame is made of, and is thicker material then the floor pan is, unless its at a reinforced pan are.

The seat belts have been added to the seat frames because it is safer. Belts attached to the seat keep you in the seat, and don't loosen up nearly as easily. Seat mounting brackets properly secured to a solid floor pan stay put in most accidents. Given a choice, if things fail, I would much prefer the added protection of me and the seat staying together rather then having a loose seat beating me up as well as me flying around inside the car.

As a side note, modern day (since the early 90s) seat belt retractors are much more sensitive to locking then the earlier versions were. Modern ones lock with a swinging weight on a lever. If it gets the least bit off center, it locks, until then its pretty easy.

I've been involved with a few rod builds that have been real life crash tested. Gene

You realize that very few cars have the belts attached to the seats, right?

The Intrepid seats he is using only have the belt buckle attached to the seat. The retractor is attached to the car. If his seat breaks free it will simply spin around backwards and spit him out. A big lot of good that will do him.

The other thing to consider is that the belt he uses may not be 100% compatible with the buckle. It might click but will it fit properly?

I'm either going to remove the Intrepid buckle end, cut it off, or just pretend for a while that it's not there... but won't be plugging a possibly incompatible tongue into it, definitely.

I also don't want one end of the belt attached to the seat and one or two of the other points fastened to the car. I'm planning to use the factory original mounting points (which are all on the car). And not an $8 Chinese seat belt either.

Anyhow, any system is only as strong as its weakest point. I may upgrade the fasteners and floor pan reinforcements. Gene, thanks for the info, can you tell me more about those "real world crash tests"?

Some day I'll have a roll bar or cage, then a whole new set of issues arises.