The not-so-definitive guide to Sienna seats

Justgosurfin

Active member
Heres the bracket that slides inside the seat, it then bolts on using the existing holes where the latches use to be located. That bracket then bolts to the slider. You have to cut out the rod that runs across under the seat. Its no longer used or needed, then you have to cut off the overhanging lip marked in red on each seat so that the bracket will slide down inside the seat. You have to cut the front of your new seat bracket at about a 45 degree angle at the front on each side so it fits inside the seat properly. Slide it in place and use the 8 existing bolt holes to secure it to the seat. DO NOT try to reuse the 4 original bolts that hold the rear latches in place. Get 4 new bolts the same size at the hardware store for each seat. The original bolts are tapered and will not tighen down far enough, they will screw in 3/4 of the way and then wedge in place and you will end up breaking them off trying to get them back out. Dont ask me how i know.... You have been warned.

You must also remove all of the latches and the cables that are attached to them as well as the release lever on the back bottom of the seat. Also note that the bracket is square, my camera has a wide angle fisheye type lens on it when i took these pics. I will post more for you tomorrow or sunday when i actually start installing the passenger side.

The side pieces on the bracket are 1/8th inch wall by 2 inches wide. The larger cross piece is 1/8th inch wall by 2"x2" angle. The smaller cross piece is 1.5"x1.5" angle. Once its bolted into the seat its about as rigid as you can get. The reason i did it this way is because when youre finished the seat will actually be offset further on one side than it is on the other when bolted to the slider. This simplified making the brackets that attach to the floor. If you just bolted angle iron on each side of the seat instead of building a bracket, one side would require a piece of angle iron 3 inches wide or more, but then a 3"x3" angle would be to tall to slide down into the seat. Side note... the smaller piece of angle is positioned where it is so as to avoid interfering with the recline mechanism as well as line up with the holes in the sliders. If you make yours like mine everything needs to be square and level so your seats arent lopsided or you damage or bend your new sliders when you start tightening bolts down. The bolt hole closest to the front of the seat on each side is offset so dont use them as a reference to build your brackets, use the other three on each side to build your bracket, then mark and drill the front holes last.
Awesome! Thanks so much for the write up. My only concern is that I won’t be able to use my swivel base with them as it will put me up way the high. Hmmm


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Justgosurfin

Active member
Heres the bracket that slides inside the seat, it then bolts on using the existing holes where the latches use to be located. That bracket then bolts to the slider. You have to cut out the rod that runs across under the seat. Its no longer used or needed, then you have to cut off the overhanging lip marked in red on each seat so that the bracket will slide down inside the seat. You have to cut the front of your new seat bracket at about a 45 degree angle at the front on each side so it fits inside the seat properly. Slide it in place and use the 8 existing bolt holes to secure it to the seat. DO NOT try to reuse the 4 original bolts that hold the rear latches in place. Get 4 new bolts the same size at the hardware store for each seat. The original bolts are tapered and will not tighen down far enough, they will screw in 3/4 of the way and then wedge in place and you will end up breaking them off trying to get them back out. Dont ask me how i know.... You have been warned.

You must also remove all of the latches and the cables that are attached to them as well as the release lever on the back bottom of the seat. Also note that the bracket is square, my camera has a wide angle fisheye type lens on it when i took these pics. I will post more for you tomorrow or sunday when i actually start installing the passenger side.

The side pieces on the bracket are 1/8th inch wall by 2 inches wide. The larger cross piece is 1/8th inch wall by 2"x2" angle. The smaller cross piece is 1.5"x1.5" angle. Once its bolted into the seat its about as rigid as you can get. The reason i did it this way is because when youre finished the seat will actually be offset further on one side than it is on the other when bolted to the slider. This simplified making the brackets that attach to the floor. If you just bolted angle iron on each side of the seat instead of building a bracket, one side would require a piece of angle iron 3 inches wide or more, but then a 3"x3" angle would be to tall to slide down into the seat. Side note... the smaller piece of angle is positioned where it is so as to avoid interfering with the recline mechanism as well as line up with the holes in the sliders. If you make yours like mine everything needs to be square and level so your seats arent lopsided or you damage or bend your new sliders when you start tightening bolts down. The bolt hole closest to the front of the seat on each side is offset so dont use them as a reference to build your brackets, use the other three on each side to build your bracket, then mark and drill the front holes last.
How high did you determine the front of seat to be?


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Justgosurfin

Active member
Sorry for the poor pics and ugly welds but this was my first seat experiment using Cadillac CTS V spec seats. Unfortunately they were not comfortable for the upright position you’re in in a van. Adapting to the swivel is actually straight forward. Just bolting the seat base to two pieces of flat bar across the swivel top. The last pic is from the discountvantruck website and more or less shows what my current swivel is. I would basically just be putting power base on the swivel top.

As I mentioned above my concern will be the added height of the 6 way base. The site says the base height is 4” when down. Did that seem accurate to you? Is your 6 way base pretty much flush on the floor? If nothing else I suppose I could chop down the pedestal.

Thanks again for diving into this!








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Justgosurfin

Active member
Yes, the base measurements are accurate. No i could not install the bases flush with the floor because the driver side has to be raised up to clear the control module under the driver seat. Your rig probably doesnt have that so it wouldnt be a concern for you. I also have a raised ledge where the floor transitions into the camper area, the bases had to be higher than that ledge so that they didnt hit it when the seat was moved back.
Thanks again for the info. I think I’m going to pull the trigger and order one of the bases and see what we can make happen.


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Coreyt

New member
So after reading through this and contacting mg, I now realize I have jumped the gun. I purchased a set of 2015 2nd row seats thinking I could just purchase the adapters and away I would go. Now I’m realizing just how wrong I was.
if I’m understanding correctly, I will need to fabricate up some adapters or spend $1000 for some?
 

Coreyt

New member
I still have a single mount for the Sienna seat (I only needed one) if anyone wants to buy it. I’m in Canada so given their weight I wouldn’t want to ship it too far.

Can’t remember if I ordered it from mgmetalworks or from u joint but it’s identical to those shown and the mate to it is still working flawlessly in my van to this day.
Is this to mount it in the front? I’m near Seattle
 

clarkh

Observer
I'll be selling my front mounts if anyone is interested. Passenger swivel. PM me. Located in San Diego.
 
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