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Seat Install with LTrack

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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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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:

View attachment 152754
Surly, Which seats are these and what does the connection go the L track look like?
 

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Surly, Which seats are these and what does the connection go the L track look like?
I have a 3-seat bench. The spacing of the legs on ALL seats matches the valleys in the floor ribs (except for the seats which have one side bolted to a wall).
All factory floor mounts sit in the valleys, never on top of the ribs.

Connector to hold seat floor mount to L-track:
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I’m going to lay out my L-track so we can secure two dirt bikes ( using Bike Binderz)in the outer two spaces or a single bike in the centre position. We would like the option of adding a 2 person bench for the times we take friends skiing or camping with us and I would like to secure the seat to the L track.
My question is , without first buying a seat,
how do I know what the dimensions/ measurements of the seat base? Is there some sort of industry standard? Is it possible to shop for a seat AFTER I have installed the L track and somehow hope it all lines up?
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There's a lot of interesting ideas on this thread. We got SmartFloor installed - it's not simply bolted in, it's bonded to the van floor (the whole install only has six bolts across the entire van floor - watch the whole video to see how it's put in). The van will fold before the floor will rip up. YouTube pull test video

Simply bolting L-Track to the floor is definitely not NHTSA compliant - doing that and saying 'I'm using L-track, just like the proper installers do' is like saying 'I'm using OEM seats so, surely just throwing them in the van means they'll be just as good as an OEM installation. Be safe and think about passengers having negative consequences if something goes wrong. And your insurance company won't help you out one bit if it's a questionable installation, so get a good umbrella policy.


Underside of L-track. Ain’t goin nowhere.
@OtterPNW Once the first bolt goes, the rest will zipper. Ask any mountain climber how that goes. The momentum of the first failure will actually work against all subsequent bolts and render them worthless.

Even if it's just holding cargo down, consider what happens if the cargo comes loose and where it's going while the van is slamming on the brakes.

Sorry to kill the mood.
 

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There's a lot of interesting ideas on this thread. We got SmartFloor installed - it's not simply bolted in, it's bonded to the van floor (the whole install only has six bolts across the entire van floor - watch the whole video to see how it's put in). The van will fold before the floor will rip up. YouTube pull test video

Simply bolting L-Track to the floor is definitely not NHTSA compliant - doing that and saying 'I'm using L-track, just like the proper installers do' is like saying 'I'm using OEM seats so, surely just throwing them in the van means they'll be just as good as an OEM installation. Be safe and think about passengers having negative consequences if something goes wrong. And your insurance company won't help you out one bit if it's a questionable installation, so get a good umbrella policy.




@OtterPNW Once the first bolt goes, the rest will zipper. Ask any mountain climber how that goes. The momentum of the first failure will actually work against all subsequent bolts and render them worthless.

Even if it's just holding cargo down, consider what happens if the cargo comes loose and where it's going while the van is slamming on the brakes.

Sorry to kill the mood.
But the zipper is a flawed analogy. Pulling on rope and biners point loads every single one, one at a time. One pops, then the load travels to the next hard point, it pops and so on. L-track loads all connection points at the same time and distributes the load to all connections not one at a time. The longer the piece of track the better. The geometry of the load changes to as it travels from the source too. Starting more vertical at the load point to progressively more sheer as you travel backward. The Unwin connectors engage several points at once in addition. It’s incredibly stout.
 

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I think the fender washer install is probably adequate, but I’m using three inch wide 1/4” 6061 aluminum plate underneath the chassis to better distribute the load (holes drilled through it for the screws come through, then washers and nuts on the bottom. It also overlaps the frame member flange for each cavity. Cheap and extra pullout insurance
 

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My question is , without first buying a seat,
how do I know what the dimensions/ measurements of the seat base? Is there some sort of industry standard? Is it possible to shop for a seat AFTER I have installed the L track and somehow hope it all lines up?
Ideally you have a drawing for the seat you want to install that shows where the seat rails are - in which case you can try to match the spacing for the L-Track.

Or you could place the L-track where you want it for your bike equipment. Then when the time comes, get a pair of stout thick wall steel tubes and mount them cross-wise in the van. You can drill holes in the tubing wherever the seat rails line up. In this case you're going to add height to the bench seat with the tubing underneath it and a lot of weight if the tube is strong enough to take crash loads.
 

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I think the fender washer install is probably adequate, but I’m using three inch wide 1/4” 6061 aluminum plate underneath the chassis to better distribute the load (holes drilled through it for the screws come through, then washers and nuts on the bottom. It also overlaps the frame member flange for each cavity. Cheap and extra pullout insurance
I’ve thought about this but isn’t the limiting factor still the washer and the nut underneath it?
Imagine just the washer and the floor, no aluminum. Either you distort the washer and pull the nut through the floor or it stays whole and you pull a circle of floor up. I say the floor wins every time.
Now reinforce it with aluminum like you are doing and again the weak point is still the washer/nut?
I’m building my L-track floor with flanged nuts and nice little square steel pieces or doubled, thick washers made of the same material depending on the bottom of the floor. So essentially very thick fancy washers and I think the flanged nut is crucial for spreading the point load on that washer.
 

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Not quite. With only the nut and washer, the washer can deform semi-easily, because the floor above it also deforms easily (and the washer surface area is still much less than a 3x12x1/4” plate). So high vertical forces in a crash would likely cause the washer and van metal floor to deform upwards together and possibly rip out. See the picture in this thread of a guy who torqued everything down and deformed the washers. This allows for a load concentration on the van floor sheet metal smaller than the washer area.

Even with thicker washers (that might not deform) the floor is still a weak point for ripping out, the washers don’t have that much surface area. So the whole joint is only as strong as the vertical force applied to a van floor surface area equal to the washer’s. Nuts and bolts have extremely high tensile strength, so the Floor/washer will deform and rip before the bolt breaks.

Just think how easy it is to dent the van floor. A single 1/4” Grade 8 bolt has an ultimate tensile strength of close to 5000lbs. Think what would happen if you loaded 5000lbs on the van floor to a surface area equal to a fender washer (hint: it would deform or rip out). The bolt/nut combo is much stronger than the van floor (until you distribute the load out a lot more).

With the ~rigid aluminum plate, the washer is essentially prevented from deforming upwards, and the vertical force is applied through the rigid plate to a much larger surface area of the floor. At that point the bolts might become the point of failure, not the floor. But I still think the floor itself might be the weak point, because you’re comparing the tensile strength of maybe 6-8 1/4” bolts (30-40,000lbs) at the rear of the seat brackets, to the vertical tensile strength of a ~12x6” section of van floor.

In another thread, I also more or less determined that the studs mounting the west brackets to the L-track might actually be the weak point regardless, not the floor
 

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It’s a lot to think about. My L-track is about 7.5 ft long and each is secured with 16-17 5/16 bolts using flange nuts and either 1 5/8 X 3/16 steel plate or 1 1/4 washer of equal thickness depending on avoiding any little frame ledges which would make the steel plate not flat under the floor. Then I have Unwin L-track connectors attached to an MG Metalworks base with only 3 grade 8 bolts per side. Forget the size but they are mammoth. 3 seems small beer but I know at least that Unwin stuff has been crash tested. These are in turn connected to Sienna seats with 4 bolts each side same size and strength. Pretty much how they came out of the van.
I honestly couldn’t tell you where the weak spot is. I just know that in a crash where I deform the floor the van will be totaled every which way and I hope whoever is in those seats is not. Really that’s all we can do after installation. That or go with a Smartfloor which has other things I’m not crazy about.
 

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DOT standards for seatbelts work out to a 5,000 lb pull strength. This can be achieved after-market with a 7/16-20 bolt in an installation where the bolt is the failure point. On the other hand, on older Honda CRV's the back seats were bolted down with four M8 bolts.

Your L-track should have a pullout strength spec. I would guess that the L-track is the weak point of your design.
 

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Does anyone know of a way to adapt the OEM 2nd row seat for a cargo van to the Unwin seat lockers . I have all the parts, except for bridging the seat bench to the L-Track on the floor!
Not a great photo... but we've got 1/4" aluminum plates bolted to the factory seats, then 3" x 1/4" aluminum angle adapting to the L-track (in our case). Full disclaimers that you will probably DIE using anything we have done with our vans; but I'll show you anyway... in case you are willing to risk your life as we are. ;)

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an update here - I finally got the floor fully installed. further up in the thread you can see how I welded the L-track mounts into the floor. Sometime soon, I'll get the seat fully installed. I installed it temporarily to get the van registered with unwin lockers. But I hate the way the lockers work, having to lift up the seat and roll it. I want the seat to slide on the L-track, so I'm making my own "lockers".
 

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an update here - I finally got the floor fully installed. further up in the thread you can see how I welded the L-track mounts into the floor. Sometime soon, I'll get the seat fully installed. I installed it temporarily to get the van registered with unwin lockers. But I hate the way the lockers work, having to lift up the seat and roll it. I want the seat to slide on the L-track, so I'm making my own "lockers".
Please post what you come up with! Currently I just bolt and in bolt the factory seat mounts into the l track which is a major pain haha
 

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an update here - I finally got the floor fully installed. further up in the thread you can see how I welded the L-track mounts into the floor. Sometime soon, I'll get the seat fully installed. I installed it temporarily to get the van registered with unwin lockers. But I hate the way the lockers work, having to lift up the seat and roll it. I want the seat to slide on the L-track, so I'm making my own "lockers".
Ever come up with some kind of locking system?
 

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Those are cool! A bit pricey for DIY folks, but I guess people spend more than that on swivel adapters.
The factory floor mounts could be bolted to them, but those are already 1.5" lift of seat height, and these would add another inch. The seat legs bolt onto the seat, so it would be easy to use a leg as a template to fabricate legs of appropriate height to bolt to the seat and the seat locker. fwiw; I think the middle leg on the 3-seat bench is superfluous. there is a 3" tube in there plus a bunch of other heavy gauge steel spanning the whole width. I removed the middle leg on my 3-seat.
 
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