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Old 10-23-2008, 05:16 PM   #1
PetersRedYaris
 
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Front seat modification. Increase thigh support.

Want to add some extra thigh support to your front seats? Here’s what I did.

Note: I’m not going to give you a step by step DIY as I don’t want to insult your intelligence. I think it’s straight forward enough.

Go to your local hardware store and pick up some metal washers, and longer bolts. The amount of washers depends on their thickness as you can make the spacer anywhere from zero to 5/8 inch thick. The bolts are a M10 x 1.25 thread. 1.5 pitch is the common thread for an M10 bolt so finding a 1.25 thread may take a few stops. I used a 2 inch stainless steel class 8.8 bolt. Class 8.8 SS is about the equivalent of a grade 5. I also found some plastic caps that fit the stainless bolt heads to make them not so bright and noticeable. (Not that they were ugly, just bright…)



Wrap your stack of washers with electrical tape as the sides will be visible after they are installed. I know I show a nylon spacer instead of washers, but the nylon spacer cracked and this DIY now recommends metal spacers (AKA- washers).



The “centering pin” for the seats will need to be bent back about ¼ inch to allow the bolts to stay centered in the holes as the seat is tilted back. I also say that the max spacer thickness is 5/8 inch because any greater and you will need to “ovalize” the holes with a round file to get the bolts to thread in cleanly.



Finish is relatively clean and unnoticeable.





This mod works well for tall drivers. This is because, if you have the seat all the way back, the seat is extended past the rear mounts, thus by raising the front you actually lower the back of the seat base.

Caution: I take no responsibility for you altering the seat mounting system in your car. As always, use common sense and don't be a fool.

Last edited by PetersRedYaris; 10-24-2008 at 04:35 PM.
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Old 10-23-2008, 09:09 PM   #2
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Nice write-up. I've done a similar mod (3/4" high) and highly recommend it if you're unsatisfied with the stock seat position. You appear to be using an grade 8.8 (strength rating) bolt. For safety, you should use the same as stock uses, grade 10.9.
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Old 10-24-2008, 09:30 AM   #3
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No, it.s not a grade 8.8 because it's metric and they use a different grading scale. Stainless is about the equivilent of a grade 5, and grade 5 is plenty strong. In the event of a crash, the threaded inserts would rip out of the floor before a M10 bolt would snap. Plus, there are four bolts holding the seat in place. Don't forget, higher grades of steel are stronger but also more brittle. I have seen grade 5 bolts bend but still hold while a grade 8 has snapped clean off. Basically, just don't use some crap non high grade steel bolts.

Lastly, if your concerned about safety, you can get about 1/4 inch rise and still use the factory bolts. Just make sure you have about 7 full turns of thread contact when you put the bolt back in.
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Old 10-24-2008, 12:26 PM   #4
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First off, "8.8" IS a metric strength rating. See this site for more info: http://www.roymech.co.uk/Useful_Tabl...s/Strength.htm

Secondly, M10 is a metric SIZE, not a strength rating.

Last edited by tk-421; 09-18-2009 at 09:55 AM.
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Old 10-24-2008, 04:27 PM   #5
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Quote:
Originally Posted by Reddog99 View Post
First off, "8.8" IS a metric strength rating. See this site for more info: http://www.roymech.co.uk/Useful_Tabl...s/Strength.htm

Secondly, M10 is a metric SIZE, not a strength rating.
I am aware M10 is the size. I am also aware that 8.8 is a strength rating, but it is a class, NOT a grade. Like I said, they are measured differently. US bolts are measured in grade and metric bolts in Class. A class 8.8 bolt is NOT the same as a grade 8. See here-

http://www.boltdepot.com/fastener-in...ade-Chart.aspx

[...]your first post says the stock bolts are a grade 10.9, which is NOT correct. Again, it's a class 10.9. You can figure out the strength comparissons yourself, just remember US (grade) bolts measure strength in PSI, while Metric bolts (class) use MPa. Heres the conversion- 1MPa = 1N/mm2 = 0.2248 pounds/mm2 And you'll need to know 1 inch = 25.4mm

Have fun...

PS- I reread my post as can see how you misunderstood me. You do realize however that both class (or grade) and size contribute to a bolts strength. I meant that an M10 bolt is huge, and there are 4 of them holding the seat in place. So long as you don't use a low carbon bolt, they will NEVER break. In a major accident, the seat will be ripped from the car before the bolts snap...

Last edited by tk-421; 09-18-2009 at 09:56 AM.
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Old 10-24-2008, 04:52 PM   #6
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Here, I'll make it easy for you. Here a conversion calculator-

http://www.chapelsteel.com/mpa-psi.html

If you want to enter the numbers yourself, you will see that my origional post stated that a class 8.8 is about equal to a grade 5, which is correct. A class 10.9 is almost identical to a grade 8.

Now that that's sorted out, If you want to say a grade 5 bolt isn't strong enough for this application, that can be your opinion.

120,000 PSi vs. 150,000PSI, BOTH will hold. And of course people are welcome to find a longer class 10.9 bolt to do this mod if they wish.
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Old 10-24-2008, 04:56 PM   #7
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Over-reaction? Maybe I had too much coffee this morning.
But I'll stand by my admonition about recommending, in a public forum, lower strength bolts for a safety related item like the seat hold-down bolts. There are a whole lot of people here who might follow that advice. Are you willing to take responsibility if someone got hurt because of it?

And remember, in a front or a rear collision, the major load on the seat would be taken by just two bolts, not four.

The original bolts are 10.9, so it's not my OPINION, it's Toyota's judgment about what is appropriate.
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Old 03-04-2009, 07:50 AM   #8
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i did this yesterday. i like it. if others are considering it- don't be scared. bolts are plenty strong enough. it changes the dynamics of the seat dramatically and ended my shopping for a new seat (for now at least...)

if pull out strength were an issue, a coarser thread (deeper thread) would've been used, and if sheer strength were an issue, a larger diameter bolt would have been used. i used a class 8.8 bolt, and have no regrets.
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Old 03-04-2009, 01:28 PM   #9
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The pin near the bolt hole, does it have a structural function or just a mounting guide?
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Old 03-04-2009, 01:32 PM   #10
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Quote:
Originally Posted by yaris-me View Post
The pin near the bolt hole, does it have a structural function or just a mounting guide?
that pin takes a good portion of the load in an accident

and the seat just holds your butt off the ground, it doesn't take any lateral load in a head on collision.

the seatbelt does, however.
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Old 04-06-2009, 10:31 PM   #11
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Good mod. I don't have a problem with the seats, but being 6'0, I think it'd be good to do this mod. I'm definitely doing the passenger seat too since one of my main passengers is 6'2, or 6'3".
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Old 04-06-2009, 11:15 PM   #12
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im 5'6" and im going to do then when i get home as well, maybe not as high though. hopefully it will give more of a sporty feel.
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Old 04-06-2009, 11:19 PM   #13
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I did this mod but used the factory bolts and didnt have to bend the pin. Made the seat much more comfortable. I used head bolt washers and just jammed as many as i could fit in there lol. So they look like a oem fitment since they are black and ofcourse they are strong. If anyone is in the bay area and wants some i got a bunch of them still leftover.
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Old 04-06-2009, 11:30 PM   #14
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Yaris sedan, so all you purchased was washers, and used stock bolts/everything else? How much difference did it make?
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Old 04-06-2009, 11:34 PM   #15
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Seat feels more comfortable. Helps keep your bum from getting store on really long trips and your theighs are more supported. And feels less like you are driving a minivan since you are tiled back a little bit instead of sitting up so high. Best part of it is you can always put it back to factory whenever you want or if you sell the car. without any signs of what you did.
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Old 04-06-2009, 11:36 PM   #16
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Sounds good, I guess I'll have to go out and purchase a pack or two of washers in the next day or two.
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Old 04-26-2009, 07:27 PM   #17
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I'm 6'4" and I never had any complaints about the yaris but I did this today and it's great. It feels sportier and increases head room. Thanks for the write-up.
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Old 09-04-2009, 11:58 PM   #18
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Thanks for the good info on the seat mod I just bought a Yaris and the seat is not comfortable at all I was looking to replace it for the foam is also to firm I will try your spacer mod and see if that helps and it would be nice if the steering wheel was'nt so ackward to reach,I just joined this Yaris site and look foward to the good ideas ya'll have.
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