Making a Height Adjustable Driver's Seat for 2009 Prius

Two and a half hours of cutting and I got what I was after ... the Prius headrest support bar shown below. Like said before, without it, the Corolla frame cannot fit Prius seatback foam/upholstery which in turn is required for the seat side airbag. That airbag is virtually required to plug the seat into my car.

While on the subject, the seatback frames of the Corolla and Prius are exact copies except for the headrest bars. I have reason to believe the seat airbag would function the same as with the Prius frame, although I have no plans to test it.



The cutting wheel shown below is very versatile. Can see the game of cutting underneath the metal because the weld bead is also underneath. Very tedious work. I broke at least 8 cutting wheels tonight. Good thing these Dremel 409 wheels come in a 36 pack. Thinking to make it in for headrest bar welding Friday morning. If not, then next week. I'm glad this cutting is over.

 

I have the black reinforced wheels too, but they make thicker cuts, and thin cuts are needed around headrest bar. Even the heavy duty 420s (IIRC) seemed too thick.

I was trying to go fast as possible last night. I only broke one the night before.

 

Ooh what a sight - a Corolla frame with a Prius headrest bar, setup for welding tomorrow morning. I chose JB Weld epoxy to temporarily hold the bar in place. I thought a self-drilling screw to temp hold the bar may cause it to shift while drilling.

I marked the bar with a scratch awl while still on the Prius frame. Also used a level to check the bar against other horizontal bars down lower. The foam and fabric should fit perfectly.



I thought about cutting this little stud from the other side, but it's not going to happen. It's spot welded in a couple places. There's a couple brackets that go over the stud to hold the fabric firm over the airbag, then a cap nut. I'll find another stud or bolt to use. There's already a hole for the stud on the Corolla frame. Like said before, the Corolla seatback part of the frame is identical to the Prius one, except for headrest bar.

 

Headrest bar is welded! I was up before 6am double checking measurements on the frame and airbag mount holes, etc before going to metal shop ... All looks good. Had to be good. I'd flip having to cut the headrest bar off again, it was PITA.

Next up is to grind and/or sand the mounts and seat rail contact points, then place the frame in the car, tack or clamp mounts in place.

I also want to evaluate the fit of the Corolla seat bottom foam vs. the new Prius foam I bought. I could get $160 back on the Prius foam. If I use the Corolla foam, pretty sure must use Corolla fabric which would mean Prius seatback fabric / Corolla seat bottom fabric. I tend to use 'generic' seat covers anyway and will be shaving foam bottom, but I'm leaning towards using Prius foam for a good looking seat.

 

It was a day of grinding and sanding the seat rails and mounts. There was some old weld bead to smooth out.

The sanded portion towards the rear of the seat rails is where the rear mounts will be welded. There is no way to bolt or rivet the mounts to the seat rails because the 'stopper' in the rails would hit the bolt (or rivet) and negate being able to slide back farther anyway.

As mentioned before, the height adjust alone would provide no more seat travel back than the stock Prius seat. This would make the project 'half baked' for me, hence the extender braces shown in photo and relocation of rear mount feet.



Tomorrow I set the frame in car and epoxy the rear mounts to set them in exact place prior to welding the mount feet outside the car at the shop. This gives a good alignment of the mounts. Even if one of the mount's epoxy breaks while taking frame out of car (like last time) it leaves an imprint of where the mount foot should go.

I hope there are no surprise fitting problems.

Time to watch the game ...

 

Front mounts are bolted on rails and floor holes line up well. Seat slides fine.



Screw jack is handy after loosening front bolt, lift up rear to make space to apply epoxy to both rear mounts



I'll wait a day and a half to pull the frame back out. I won't be surprised if the left rear epoxy breaks like last time, but if it does, it will leave an imprint of where it's supposed to go. I don't know of a portable, in-car tack welder device, but that would be nice to have right now.

 

Just having a little fun seeing how low the seat goes with some Corolla cushion on it. Seat looks like heck right now, but it will be nice when done. I'll put the new Prius foam on there to see how it looks too.



edit - The Prius foam does not tilt down as much as the Corolla foam with frame fully lowered. Each foam cushion is shaped differently yet both fit on the frame. This means after welding*, I ought to sit on both foam bottoms and decide. The fabric bottom on the bent 05 Corolla frame is Gray and is in good shape.

* scary thought, but if I sat in the seat now, it would ruin everything - the right rear mount would rotate and collapse, a front brace might bend as well as the frame. Got a 'do not touch' sign on the frame just to remind myself.

 

I went to Lowe's looking for a stud like the one welded in the Prius frame. A couple brackets go over the stud which pull the fabric snug in the airbag area. I knew the stud was an M6 x 1.0, 8mm long with a large, flat, blank head. I looked around but didn't see at Lowes.

So, I cut the frame around the stud.



.... and spent a half hour cutting away the frame material while holding stud (on left) with pliers. I can reuse this and that's a good thing.



Next up is to pull the frame carefully out of the car tomorrow afternoon, wait a couple days and have the mounts welded.

 

The frame is prepped and ready for its last session to weld all four mounts and tack the threaded stud.



I put some foil tape to seal off the inner rail slots, keep sparks out.



I'm looking at Thursday or Friday morning for welding. This week for sure.

This week is much easier. Time to take apart the 05 seat for a few Gray colored trim parts.

Later...

 

The first time I thought about taking a seat apart (without reading Toyota's disassembly instructions ) last May, I gave up after about half an hour.

Reading the instructions helps. To get a side trim piece off, there's a tricky little claw in the crevice between the seat bottom and seatback. I happen to have this curved screwdriver hanging around.



Once finding the right slot, I press away ...



and the claw releases (sometimes it gets a little chewed up). There's a proper tool somewhere for this, but I'm not buying one.



This piece will end up on the finished seat.



I used to think taking the seat apart was a mystery and would need to use an upholstery shop to have it done. Nah. Taking trim and upholstery off is not bad. Doing the metal work - cutting, grinding, sanding, prep for welding .... time consuming!!

 

Mounting feet welded on this morning! Went well.

Looking for better paint to make weld areas look nice again.

Painting, foam shaving and reassembling coming up. I might finish within a week.

 

Finally found semi-gloss black enamel at a hobby store. Doesn't match the black on the rails but that's ok.

 

Edit 8/6/10 If shaving in to side bolsters of foam, best to shave a little, then put foam bottom on frame in car, drive around (will need seatback upholstered of course and use seat cover)

Note - in pic below, too much is shaved out of side bolsters.

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I spent the day shaving this brand new $200 Prius seat bottom foam. I like how it turned out. Still Prius-like, but 1 1/2" wider on the flat portion and the raised sides are relaxed. I used a rotary cutting bit, electric knife and rotary grinding bit on the foam. And lots of vacuuming up the foam dust.



I'm all ready to start reassembing the seat, tomorrow.

 

I discovered a minor problem this morning when trying to mount the seat belt latch and wire harness - the Prius seatbelt latch arm is 2" longer than the Corolla (and that makes sense since the Corolla frame can lower 2" more). I knew there's no way I'm going to drive around with a lap belt not even snug.

But, I thought the parts must be interchangeable. Turns out there is an similar black electro-mechanical switch that plugs into the seatbelt latch. There's a claw underneath, push to release it. The Prius switch plugs into the Corolla seatbelt latch just fine.

Wire colors are the same on these Prius and Corollas switches. I checked out the continuity at the connector pins on the Corolla with seatbelt unlatched and latched, then plugged it into the Prius harness. It behaves the same, so it should work fine.

 

Today was a day of lubing the seat frame, dealing with the problem of different size seatbelt latch arms, wiring, adjusting seat position sensor, attaching fabric to new seat bottom foam, fitting foam and fabric to cut hole for height adjuster mechanism.

All that's left to do is bolt on the airbag, reassemble seatback and seat bottoms onto frame, attach the trim. And place in car. Not tonight though, I'm wiped out.