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Discussion Starter · #1 ·
Hi all,

I recently got my van and I'm starting in on the build. First things first, I'm trying to install a bench seat for passengers.

I'm sure this has been posted a million times. I'm trying to do the install in the safest most professional manner possible.

Here's how I'm planning to do it. Looking for feedback.

Materials:
I'm using l-track that's 7075 aluminum (the stronger stuff)
I have all grade 8 bolts, screws, nuts, washers
I'm using 1/2" thick 6061T6 aluminum l-bracket as my underbody reinforcement

Here's some pictures that render what I'm planning.

The blue are the 6061 l-brackets that will run along side the transit crossmembers
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The 6061 plates will be bolted, see grade 8 bolts in red. The l-track would mount through the floorboard to the l-brackets, see grade 8 screws in yellow
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Here is what the installed chairs would look like, mounted on the l-track, allowing for easy removal.
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Discussion Starter · #2 ·
Now I'm mainly concerned with attaching to the crossmembers in the correct manner. So the question is, is my plan good? See detailed pics:

The red bolt is a grade 8. The yellow screws for the l-track would have washers and nuts (not pictured).
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The cyan cylinder is an anti-crush sleeve to make it so that tightening the bolt will not crush the crossmember. The crossmember would be drilled such that the hole on one side matches the bolt diameter and the hole on the other side of the crossmember would match the diameter of the anti-crush sleeve. Contrary to transit BEMM instructions I would not be welding anything (I would try to get the sleeve size to match the crossmember and paint everything for rust protection.
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Hopefully you can see in this cross-section how the anti-crush sleeve would work. Again note it would not be welded into place, just held by all the hardware.
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So what do y'all think?

Again, I'm trying to be as safe as I can here. What I'm not sure is whether drilling in the subframe in the spots indicated is safe. There is a BEMM document that spells out "no drill, no weld" zones, but I couldn't tell exactly where was indicated.

I've called a couple of my local shops and to consider just paying for a professional install. I'm not confident that their plans are great, they basically want to put a bolt on either end of the ltrack through the crossmember and then drive in sheet metal screws every few inches along the l-track.
 

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You don't need to tie into the frame and in fact, the BEMM (Para 5.1.6) states:
"Do not drill into closed frame body members"

The biggest problem when teaching to the floor is tear-out pulling the fasteners through the thin metal which the BEMM 5.1.6 alludes to with: "Spread bolt loads to minimize local stress"

I've also mounted L-track to the floor in an aluminum body F-150 and other steel bed trucks to tie down motorcycles and been fortunate to never have the ultimate test of an accident. Even so, with 1/8-3/16" thick bearing plates under the floor and using every possible* bolt hole from the L-track, some rough calculations and common sense indicated that I could turn the truck over with some G's and the bikes would stay attached. The anticipated loads were for a 600# adventure bike, which would be pretty close and maybe a bit more than your 3 person bench.

btw - For corrosion protection my bearing plates were glued in place. (Probably was D0W 4200 or 5200?)

I'm sure you are aware you're going to need to drop the gas tank and account for the floor too. If you get it put together with the seat, work on the interior, and then come back to add the floor it'll mean dropping the tank a second time.

* Adding the bearing plates really was not that big a deal, it just took a bit of planning to get as few L-track bolt holes as possible to be over frame cross members.
 

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If a floor is added you cannot take out the L track and install it back over the wood floor. The track needs to sit on the metal floor with nothing in between.
Now if you wanted to raise the track to be even with the floor you could put a drilled metal bar of some thickness below the track but no wood, no minicell, nothing that’s compressible.
This is so you can tighten all your yellow bolts to the proper torque. Can’t do that if you are compressing material in between.
The horizontal through bolting of the frame is unnecessary.
I am not an engineer. This is my opinion based on input I have sought over the last year. I’m taking delivery of my van in June and am putting two Sienna seats in it.
 

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Discussion Starter · #7 ·
If a floor is added you cannot take out the L track and install it back over the wood floor. The track needs to sit on the metal floor with nothing in between.
Now if you wanted to raise the track to be even with the floor you could put a drilled metal bar of some thickness below the track but no wood, no minicell, nothing that’s compressible.
This is so you can tighten all your yellow bolts to the proper torque. Can’t do that if you are compressing material in between.
The horizontal through bolting of the frame is unnecessary.
I am not an engineer. This is my opinion based on input I have sought over the last year. I’m taking delivery of my van in June and am putting two Sienna seats in it.
I'm not planning to have any added flooring between the ltrack and the transit floorboard.

Since the l-track is 1/2" high, it may sit lower than the rest of the floor (currently thinking polyiso+plywood+coin vinyl floor). I may get little strips to plug the hole when seats are in and maybe additional plugs for when the seats are out...
 

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Discussion Starter · #8 ·
You don't need to tie into the frame and in fact, the BEMM (Para 5.1.6) states:
"Do not drill into closed frame body members"

The biggest problem when teaching to the floor is tear-out pulling the fasteners through the thin metal which the BEMM 5.1.6 alludes to with: "Spread bolt loads to minimize local stress"

I've also mounted L-track to the floor in an aluminum body F-150 and other steel bed trucks to tie down motorcycles and been fortunate to never have the ultimate test of an accident. Even so, with 1/8-3/16" thick bearing plates under the floor and using every possible* bolt hole from the L-track, some rough calculations and common sense indicated that I could turn the truck over with some G's and the bikes would stay attached. The anticipated loads were for a 600# adventure bike, which would be pretty close and maybe a bit more than your 3 person bench.

btw - For corrosion protection my bearing plates were glued in place. (Probably was D0W 4200 or 5200?)

I'm sure you are aware you're going to need to drop the gas tank and account for the floor too. If you get it put together with the seat, work on the interior, and then come back to add the floor it'll mean dropping the tank a second time.

* Adding the bearing plates really was not that big a deal, it just took a bit of planning to get as few L-track bolt holes as possible to be over frame cross members.
Thanks for the detail and info, just what I'm seeking.

I believe what you're referring to is found in 5.1.1? But I think that may be limited to body members. Meaning inside the vehicle?

I was looking at 5.15.1 which shows drilling, welding, and bolting.

Does the BEMM refer to Transits that are both unibody and body of frame? Or all the all unibody? I'm confused on this point.
 

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I bolted my seat to L-track, some things I did simpler like I welded a c-channel piece of steel to the floor then bolted the l-track to that. The thing that I did that very much complicated it was that I chopped the legs off and welded my own frame. This allowed me to have an 18” square where the frame bolts to the L-track and now I am able to mount the seat forwards or sideways.
Your idea looks good, are you using a 3 person bench seat or an aftermarket.

152716

extra bracing was put in the back of the seat, this was before it was completed.

152717
 

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Discussion Starter · #10 ·
I bolted my seat to L-track, some things I did simpler like I welded a c-channel piece of steel to the floor then bolted the l-track to that. The thing that I did that very much complicated it was that I chopped the legs off and welded my own frame. This allowed me to have an 18” square where the frame bolts to the L-track and now I am able to mount the seat forwards or sideways.
Your idea looks good, are you using a 3 person bench seat or an aftermarket.

View attachment 152716
extra bracing was put in the back of the seat, this was before it was completed.

View attachment 152717
I really dig the idea of being able to rotate your 2 seater for forward or side facing. Cool.

Currently I have a 3 seat ford oem bench from a transit passenger version. I am still scratching my head about how to mount it to the l-track. One way is using the ford rail on top of the l-track. Another way would be to find a different seat entirely. Also your leg swap with weld is a new idea I'll consider.

I'll tackle that issue in a bit, but mainly want to make sure I've got the right approach to attaching the l-track to the vehicle (the cross members specifically).
 

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Also, dinocarsfast, how did you attach your c-channel on the underside?
Underside? I welded the C-Channel directly to the raised bumps on the floor, spacing was perfect for my floor with a little insulation. You could probably make the original floor mounting work on top of the L-track.
Mine mostly sits sideway now but I think its nice that I could face it forward if I wanted
 

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L Track was originally designed to locate removable seats in aircraft, often using blind rivets through the aluminum floor and the webs of its stiffening ribs.

IMHO, all you need to to is add load spreading plates or washers and use all of the fastener holes in the L rack. I cant imagine the loads from a survivable crash would pull the L track out of the floor.
 

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Discussion Starter · #14 ·
Underside? I welded the C-Channel directly to the raised bumps on the floor, spacing was perfect for my floor with a little insulation. You could probably make the original floor mounting work on top of the L-track.
Mine mostly sits sideway now but I think its nice that I could face it forward if I wanted
Got it, thanks
 

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Discussion Starter · #15 · (Edited)
L Track was originally designed to locate removable seats in aircraft, often using blind rivets through the aluminum floor and the webs of its stiffening ribs.

IMHO, all you need to to is add load spreading plates or washers and use all of the fastener holes in the L rack. I cant imagine the loads from a survivable crash would pull the L track out of the floor.
The floor is just a tin can. So even if the fasteners don't pull out of the floor, the floor itself could be the problem, right? I'm imagining the whole floor section coming out like a zipper...

On the transit passenger van, ford welds the seat brackets to the crossmembers...
 

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Do what you want, we all overbuild a lot of things but I think the seat brackets welded to the crossmembers has a lot more to do with speed of assembly than safety. If your in an impact that’s so bad that the floor rips open like a tin can because the seat is bolted to it I don’t think anybody would have survived that crash even if the seat was bolted to the frame rail either. I think a backing plate underneath would suffice.
 

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What anti crush sleeves were you looking at? I don’t think it’s a bad idea to do a few through the frame members, even if it’s not recommended in the BEMM. But it is overkill and not necessary IMO.

For my seat install, on the underside I’m going to have wide steel plates that the l track bolts through the floor into to distribute the load.

On top of the floor, 1x1” aluminum bar the length of the l track (front to back in van), sitting down in the grooves.

Then the flanged 7075 l track bolts through that. This puts the flange just over my flooring (.4” insulating between ribs, 1” polyiso on top of ribs, 1/2” plywood on top of that, .1” vinyl on top of plywood.

The top of the l-track must be level or above your flooring for the seat brackets to be able to bolt to it properly. It cannot sit lower than the rest of the floor unless you build some kind of spacer for it. Which is certainly doable.

I decided I’d accept the l-track flange sitting .1” above the floor, so that there’s is not room for water or dirt to get down into the subfloor (and the vinyl can’t peel up around the channel)
 

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The floor is just a tin can. So even if the fasteners don't pull out of the floor, the floor itself could be the problem, right? I'm imagining the whole floor section coming out like a zipper...
No, the floor is not that thin and helpless, especially with the spaced ridges for stiffening! As I and now others have pointed out, you just need to have load distribution on the bottom to spread the load across the face of the sheetmetal.

You don't need to drill the frame members and are adding new potential problems. In addition to the BEMM cautioning not to, off the tp of my head these could include:
1. Having a floor that can have a small amount of flex over the edge of a corner of an immovable piece of angle means that the floor will eventually crack along the edge of the reinforcement. If you just add something to spread the load, there will be less flex along the edge.
2. The frame section width will not be absolutely even along the length, meaning that each crush tube will need to be made for each hole.
3. With the tubes not welded in, there's a new opportunity for frame rust.

etc. . .
 

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The floor is just a tin can. So even if the fasteners don't pull out of the floor, the floor itself could be the problem, right? I'm imagining the whole floor section coming out like a zipper...

On the transit passenger van, ford welds the seat brackets to the crossmembers...
No it really isn't and no it really won't - especially if you add load spreading washers or plates to back up the fasteners. The floor is bonded to the cross beams and rails. You should consider the whole underneath as a structural side of a giant braced box section. Its not that different to an airframe. The Transit body is really very strong, far stronger than the body-on frame E Series that it replaced over here.
 

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The OEM method for mounting the passenger van seat brackets is to have a wide washer/plate that overlaps the flange of the underbody support beam. You don't need to add all that extra bracing if you just do what the factory does. Of course, the factory seat legs are at exactly the right width to drill through the floor and use a plate to overlap the flange right next to the hole you just drilled.

My L-track mounted on floor with stainless fender washers overlapping the flange underneath:

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