Plan for relocating seats!

I have finally settled on a plan for relocating the front seats 2 inches further back. I have a 36" inseam and size 16 feet, so the Prius is a tight fit.

I spoke with a local welding shop and a local nuts and bolts supplier.

Here's the plan:

1. Grind off the rivets holding the two front and the outer rear mounting bracket to the seat rail.
2. Weld material onto the front two brackets to make them longer.
3. Fabricate a bracket for the outer rear location that will sit in reverse position from the current one.
4. Attach the three modified brackets to the rails using m10-1.25 (10.9 hardness) button-head bolts and 10.9 hardness flange locknuts on the bottom.
5. Drill new hole in floor for inner rear location. Weld steel plate and 10.9 hardness flange locknut onto underside of vehicle in new location.
6. Bolt seat to the floor, now 2 inches further back.
7. Relocate Hall sensor so Airbag will inflate with proper force (process TBD)
8. If the seatbelt sits too low on lap, repeat relocate procedure for lower (outer) seat belt mount.
9. If the seatbelt sits too far away from shoulder, add belt holder from a Camry coupe or similar to hold seat belt at proper position.
10. Add a fixed plate to permanently raise the front of the seat slightly.

The welder said he would do the work for $200 per seat; I'll likely undertake this in about two weeks.

I have given a lot of consideration to a drill free, bolt in solution, but I haven't come up with something. Theoretically, I could create a kit that consisted of three brackets and some bolts that others could buy, but I haven't figured out a way around drilling a hole in the body for the inner rear mount. The seat belt receptacle needs lots of strength at that point and a "reverse" bracket like I will be using at the outer rear location is likely not strong enough.

I also will not be crash testing my design, so it's hard to say if it will be effective in a crash. I'll try to make it significantly beefier than necessary but we may never know if it will hold until that fateful day.

Nate

 

Yes, step 7 above (Hall? HAL? sp?) sensor.

I'm looking into this as well.

Any other considerations anyone can think of? Better ideas? I'm open to suggestions.

Nate

 

Okay, looking at the manual, I just had another brainstorm. For the rear outer mount, instead of fabricating a new one, why not just grind the rivet out and mount it further up on the track? Very little force is applied to this part of the seat in a crash anyway. This would allow me to keep the current mount position on the floor. I'm considering doing this on the inside rear one as well, but man, that IS the seat belt anchor, so I'll have to inspect it closer to see how the loads transfer in a collision.

As far as the "Seat Position Airbag Sensor" goes, I will just mount it two inches further forward to compensate. I think this should work; the only question is what the sensor senses? (A magnet somewhere?)

Anybody know?

Nate

 

Okay, I've looked at the repair manual. It appears I need to mount the sensor 2 inches further BACK instead of forward since it's relative to the seat rail.

If the rail is moved back 2 inches, then the rail would be in the "overhang" position 2 inches sooner (as you slide forward). This could cause the SRS to use lower inflation force even though you are not as close the system believes. Moving the sensor back 2 inches would it prevent it from sending this false signal.

Nate

 

Dan, that is not correct, I realized that the sensor detects only one of two conditions:

1. The presence of TWO rails beneath it
2. The presence of ONE rail beneath it

When it is detecting ONE rail beneath it, it will believe that the seat is very far forward. If I leave the sensor in place, it will detect the "forward" position when I am actually 2 inches further BACK. If I mount the sensor 2 inches BACK, it will detect the "forward" position at the exact same location as before.

Here's an example: (Numbers are hypothetical).

Let's suppose the sensor detects "forward" at 10 inches from the steering wheel. Anything further forward is "forward;" anything further back is "back". Let's suppose that my wife's normal driving position is 11 inches from the steering wheel. The sensor will detect this as "back". If I relocate the rail system 2 inches rearward, the same sensor position is now actually 13 inches, but the sensor reads 11 inches. My wife now slides the seat forward 2 inches back to her 11 inch position. The seat sensor now reads 9 inches, even though she is at 11 inches. If I move the sensor forward 2 inches to compensate, it would read 7 inches when she is really at 11 inches! However, if I move it BACK 2 inches, it will read at 11 inches when she is at 11 inches. (An accurate reading).

Perhaps this diagram will help:

 

Yes, the diagram is from the Toyota Repair manual mentioned. However, it is from the electronic version, available page by page (no bulk download available) from techinfo.toyota.com. The manual is very, very good. It is readable like a book for those who are only slightly mechanically inclined but is also a detailed reference for those who are experts.

Dan, I'm glad you agree on the sensor. It confirms that logic is correct.

Nate

 

So, you want an update?

The short answer: I've been busy, I haven't given up, it's on the list.

The long answer? I have a new baby, so the mods pace has slowed quite a bit. No, I haven't given up on my plan, it's just that my wife is requiring me to finish my household "mods" first. The good news? My sprinkler system is almost done!

Anyway, the only thing about my mod is that it isn't all that useful to others. I'm going to have a welder (a person) do just about everything; unless you live near Longmont, Colorado, you will have to find a welder in your area.

I had originally planned to assemble and sell "Bolt-in" kits, but after failing to establish a market for my lock-mod, I realized most people just aren't willing to pay enough to make it worth while. I had originally thought that the "interested posters" were a small sampling of the available market. For example, for 10 posts there would be 100 buyers. Instead, I've learned it's the other way around, for 10 posts there's (maybe) 1 or 2 buyers. It's just not worth my while. Take your Prius to a local welding shop and get an estimate, mine is about $200 per seat.

On a side note, I'm also holding out hope that the 2006 Prius will have an adjustable seat and I can switch out the seat rail assembly. We'll see.

Nate

 

If I am able to retrofit a 2006 electric seat to my 2004, I will of course post all of the needed info to do it yourself.

But, I won't be selling any kits or anything.

Nate

 

Pay close attention to the inside rear mount. It takes the brunt of the force from the seat belt receptacle and transfers that load to the car.

The other three mounts just hold the seat and the occupant comfortably and contribute somewhat to crash protection. That right rear one, however, is critical that it not be compromised.

My plan is this: Grind off the rivets at the front of the track that hold the mounts to the track. Weld more material to the mounts to extend them. Using "button head" bolts of very high strength (and "Type C" nuts of equal strength), bolt the new, longer mounts to the track at the existing location on the track.
-For the rear, modify the outer rear mount so that it sits 180 degrees from how it sits now. Bolt the mount, in a new hole if need be, to the existing track.
-For the inside rear, I plan to remove the carpet and padding from my desired location, then drill through the body, and weld a thick metal plate on the backside, and weld a nut to that. Then bolt the inner rear mount in the new location.

I have yet to look under the car to determine if there is enough clearance in the area I wish to drill and weld. That could happen this weekend, but I don't know.

My goal is to go back 2 inches; this is a lot, since it accomodates your thighs only, it theoretically compensates for 6 or more inches in a person's body height.

One last thing, I need to relocate the airbag sensors (discussed above). I really don't think this will be a problem.

I've also considered if anything needs to be done with the seatbelt, but it looks like it won't be a problem.

Nate

 

NOT verified. TBD.

Nate