Thread: Seat & Seat Belt Mounts

Tweet

Fiberglass body, core-mat reinforced floor , bolting in bucket seats, one 3/8" bolt per corner. Is it necessary to weld tabs/plates to the frame to catch these bolts, or are fender washers on the bottom side sufficient? With buckets this is much more of an ordeal than for a bench.
Same for seat belts - mounting hardware welded to the 1x1 tube body reinforcements, or through bolts in the floor, using their large (2"x3") nut plates?

I'd be doing the weld program if I intended to drive the car on the street. I don't have my Machinist Handbook handy but I'd venture that the force from a crash, even a mild one, would pull those fender washers right through the glass body.

Just my opinion.

REGS

Roger - you need some reinforcing for those seats. Fender washers are not sufficient to hold a bucket seat through a fiberglass floorboard. I trashed the Brookville supplied soft, draw quality 22ga steel floorboards after kneeling on them and having them bend under my 200# weight. I had a double 16ga floorboard made up and then welded up some .500 square tubing and put that in the middle - i.e. meat in the sandwich along with some insulation. I added some tabs on the tubing web then through bolted the seats. These floorboards are in turn bolted via many Gr5 .25 bolts to the body sub frame. I would, in your case, probably make up a steel tubing web, bolt to the underside of your floorboards then bolt your seats through that. Is it necessary to fasten to the chassis? Probably not. Additionally, you could allow for your seat belts to bolt to that seat frame too - which I did as well.

For whatever reason, I don't seem to have any pictures of the assembly - probably because I was 'between cameras' when I was doing this part.

Hope you can figure out what I said If not let me know if interested

Food for thought.
In a crash the body will most likely leave the frame. Therefor . if you are held by the sdeat belt that is welded to the frame may not be a good idea.
May be that you want to stay with the body and have that protection around you rather than the body trying to go around you.

Use two, minimum 2" x 2" x 0.083" wall square tubing welded framerail to framerail to mount front and rear of seats. Make whatever provision you have to to clear transmission/driveshaft. Mount lap belts and crotch straps to rear crossmember. DO NOT mount shoulder belts to this crossmember. Shoulder belts must be anchored height of shoulders to prevent compression of spinal vertebrae on impact. Engineer the package so that the body and frame remain as a unit (translation: Use lots of bolts and nuts and big flat washers).

Evidence of my being uncomfortable with the fender washer approach, which had been suggested to me by a local guy, is me asking the question here. Regs, I share your concern about the forces involved and the strength of the floor, even with Core-Mat. IC2, I understand your "sandwich" approach and it sounds secure, but applying it to my glass body is a bit different. CCBob, your comment is one that really makes us think - this is a fiberglass car, so any crash of significance is going to put us in a world of hurt. Recall KennyD's pictures a few days back of the Willy's that broke up all around him. Tech, as usual you cut to the chase with specifics, which I expect are based on your understanding of the rule books for comp cars. While the body may be separating from the chassis in a wreck, your approach is to ensure that the part with the seats remains a unit, which makes sense to me.
I attached a picture from N&N's website showing the basic chassis - American Stamping rails with a round tube bracing section between, sort of a modified X-member with upper & lower sections. The upper section is at, or very close to contacting the bottom of the body - within 3/16" at the widest point in the area of the seats. Tomorrow I will spend some time laying under the car pondering the layout, and how best to anchor the seat bolts while keeping it presentable. The body is coming off very soon for final frame work, prep and paint, so the timing is not too bad.
Thanks to all who took time to respond.

I will agree with techinspector1 in asmuch the seatbelt should be mounted correctly for not only safety but also comfort. I find it difficult to understand why some people believe that in a crash, the body will seperate from the frame... If constructed correctly no car should fall apart like that... When building my Bucket I constructed a special crossmember with outriggers solely to mount seatbelts that when the body is fitted the seatbelt bolts pass through the floor into the crossmember mounts. The should height seatbelt mounts are welded into the heavy 3mm wall rollbar that is bolted directly to the chassis/frame. I personally find that the seatbelts in my bucket are far more comfortable than the stock belts in my BMW coupe, as they don't slide up my shoulder and cut into my neck.. As tech says..... use heaps of bolts / fasteners to attach that body....

This thread has made me look closer at the whole body/seat/seat belt mounting from a system approach rather than as individual components, which is the right thing to do. I will probably have more work to do than I had anticipated when I pull the body from the frame, but it will hopefully result in a safer overall approach.

Search for street rod wreck pictures, you will find that LOTS of glass bodies leave the chassis. I'd definitely mount the seats and belts to a crossmember or piece that you fabricate that is attached to the frame. Also i would be finding a way to keep a 'Glass body attached. Min'e steel and i am still beefing up the mounts and body structure so that it won't leave the frame in the event of an accident.

Sorry, I have no photos but here's what I did.

I made a couple of seat frame mounts and the rear seat mount also serves as the mount for the seat belts. The rear mount is 1"x4" thick wall tubing. It's secured with grade 8 bolts welded to make studs. They go through the floor pan and then through the frame cross member. The seat mounts to a couple of welded tabs to this mount. For the belts I used nuts counter sunk into the bottom of the 1"x4" tubing. I'm comfortable that the seat and belt mounting would pass "TECH 1's" inspection, which is good enough for me, LOL.

In my 32 I used 2" angle (3/16) that spans the frame rails directly behind the seat on the floor and mounted the seat belts to it. The angle is bolted thru the body into the frame via 2x1/2-13 UNC grade 8 bolts using existing body mount holes/nuts welded inside the boxed frame. The angle iron is viewable inside the car; function before form applies here for me.It is designed to restrain my fat butt and a passenger's in at most a moderate low speed street type crash.

Like the vast majority of older model hobby cars my car ain't designed for crash safety at the strip nor energetic collisions (over 45 mph) on the street in most cases. It is what it is ......................

Kitz

Seat belts and seats need to be anchored together. A seat belt to the frame and a seat to the floor do not move together in a crash. As the floor and seat pull away the belt gets short (owch) Frames do not always bend in the same direction as the body.

It seems we have some differences in approach regarding seat and seat belt mounting. The NSRA May 2010 Street Scene Safety First column on page 156 (thanks, Mike52) includes an article on seat belt safety by Charley Bryson who is on their Southern Illinois Safety Team, and they stress that seat belts should never be mounted to the frame (assuming that the seats are mounted to the body) due to the potential for body & frame to separate, or as 53 Willy’s points out, frames and bodies don’t always bend the same way. They also call out specifics of mounting, using 2”x4”x ¼” plates beneath the floor pan, which happens to be exactly what Juliano’s provides with their belts.
After a lot of thought I believe that 53 Willy’s hit upon the most critical point – Seat belts and seats need to be anchored together. I also believe Kitz is right – most street builds are built for moderate crash safety. Race rules only apply if you have all the race goodies, like roll cages, etc. Tech, your “engineer the whole system” takes me down this path – tying it all into a package that stays together, which I’m not sure can be guaranteed for a “normal” build. Considering a typical three point mount the retractor and center belt end will be anchored to the floor, and the upper pivot will be mounted at or above the belt line which makes it a body mount – no other option. With that in mind, I believe the key drivers are:

1) Both seats and seat belts need to be anchored together, all to a common structure. Differential movement between anchor points can kill a driver or passenger that may have otherwise survived a crash.
2) For a street car without an integral roll bar system, since the shoulder harness pivot cannot be a frame mount, then all seat and seat belt mounting points should be body mounts to account for potential differential movement of body & frame in a crash.
3) Seat mounts and the two lower seat belt mounts need substantial under floor reinforcement to prevent pull through to the extent possible. Reinforcement plates that tie two or more mounts together over a wider area are a plus, especially for a glass bodied car.
4) For a glass bodied car body to frame mounts, reinforcement plates above the floor should be significant. Use of 2”W x ¼” thick plates tying two or more body mount bolts together may help keep body and frame together in a crash.

I have not yet finalized my approach and I know this may be an emotional subject, but I welcome comments on my key points above, pro or con. I really don’t want to become a statistic due to something that can be avoided by doing things different.

Roger,

What you described is pretty much the method I used. While I expect the body to stay attached to the frame in case of an "incident," I did not want to be the "cotter pin" that held 1000 lbs of body to 1800 lbs of engine and frame via the seat belt. If God forbid, the body comes off the frame, the seats will still be attached to the body, as will I, because of the seat belt.

I used 4 plates per seat. Each plate had a hole drilled in it with a grade 8 bolt inserted. The head of the bolt was tacked to the plate. Then, I inserted the bolt through holes in the floor pan and glassed them in place. That way, I had studs sticking through the floor, and didn't have to crawl underneath the car again to install or remove the seats.

Here's something I see missing with the seats/belts anchored together gig. It's called inertial loading. Seat belts are all about being respectful of Newton's first law which states in short 'objects in motion tend to stay in motion'.

My bench seat weighs 50 lbs. I weigh 320 lb. If I anchor myself to the bench seat and expect it not to fail then the seat mounts better be able to handle the sudden forces associated with deccelerating 370 lb. If the seat is anchored by itself then you can see these fundamental forces are reduced a factor of 7.4.

That said I too like the idea of a plate beneath the floor on glass rods to spread the seat load points out, but I'll make mine aluminum. That will more than hold the seat for any minor fender benders that could be survivable in a glass '32. I still like anchoring my big butt to the frame though ..............

Kitz