The folding rear seats are pretty easy to remove. Once you fold them down, flick up the piece of fabric (held down with Velcro) at the bottom of the seats and this will expose a bolt on each side. Undo those two bolts and each side will separate from the center hinge. On the other side of the seats (towards the doors) it will be held on by two more bolts. Remove those and the 2 folding seats should come right out. This will now expose the center bracket and two side brackets. Remove the three bolts holding the center bracket to the floor. Now this is where things get tricky - The two side brackets are spot welded to the body of the car, so you must use a drill to drill through the spot weld on each corner (4 in total). The metal isn't very thick so it doesn't take much to drill through, but make sure your drill's battery is charged up before you leave home.
Don't forget to grab the two seat latches, the two side cushion hooks and the plastic covers behind the seats while you're there. These are all very easy to remove.
When it comes to installing the brackets in your car you must ensure that you put them in the exact right place as alignment is the key. Fortunately for the side brackets you'll see a rectangular shaped 'hump' on each side, which shows the general location of where each bracket should sit. The center bracket doesn't have any markings however, so the best idea is to take measurements at the junkyard from every possible angle in relation to where the holes for each bracket should be. For example: Measure the distance of the middle of each hole to the rear of the car before the trunk starts, to the front of the car before it dips down to the floor etc. Write those figures down and then measure your own car, using a marker pen to mark where each hole should be. Double check and triple check your measurements to make sure you've got it as close as possible to where Toyota had designed them to be on the folding rear seat models.
Once you're confident that your measurements are correct you can begin drilling the holes for the brackets. With the holes drilled you'll have to put a nut on the other side of each bolt. I strongly recommend using stainless steel bolts, washers (2 for each bolt) and Nyloc nuts. This will ensure they won't rust or come loose due to vibrations. The bolts for the side brackets will come out under the rear wheel wells, so it's easiest to remove your wheels to get them nice and tight (unless you have crazy high fender clearance and can get your hand in there with a spanner to hold the nut while tightening the bolt from the inside). Getting the nuts on the bolts for the center bracket is a bit trickier as they come out between the trunk well and the fuel tank. When you're lying under the car you'll easily see them however, so the easiest way is to slip on a washer and then put the nut on the end of a socket with an extension. Wind the nut on by hand using the extension and then tighten the nut as tight as possible with a ratchet while someone holds the bolt from the inside with a spanner.
Now that the brackets are out of the way, you can fit the seat latches and side cushion hooks. Fortunately Toyota has already put the holes for the latches and the hooks in place, but unfortunately the holes aren't threaded so you can just use a nut and a bolt to hold each latch and hook on with.
You can now begin bolting the seats to the brackets and installing the two side cushions. Test that everything lines up right and latches into place. Finish up by installing the two plastic covers that are seen when the seats are folded down and you're all done. This sounds like a A LOT of work, and I won't lie, it does take a bit of time and patience, but it is WELL worth it. Doing the folding rear seat conversion was one of the best mods I've ever done to my Corolla and has come in handy for everything from transporting parts to sleeping in the back of my car overnight when going out of town. As long as you take your time, get your measurements right and have all of the parts you need prior to starting the job you shouldn't have any issues
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