DIY Trunk Brace

[razasasin]

On Friday I 'made' and installed a trunk brace similar to those available for purchase. I have an '08 fa5 - this should work on any '06+ Civic. For now, no pics. Will update asap with pics. Read all the way through before attempting this - there are some tips at the end I'd have for anyone else that will do it. It is pretty easy if you have tools to cut and drill aluminum. You will need -
*1 4' piece of aluminum angle or rectangle bar - at least 1/8" thick x 1"x1", I used 1/8" x 1&1/2" x 1&1/2"
*Something to cut aluminum - only straight cuts are needed so a hack saw would do - I used an angle grinder with a cutting wheel. Cut-off wheel on a dremel may do the trick
*4 1/2" x 1" bolts, nuts and washers
*Utility knife to cut carpet
*Socket and wrench to fit the bolts and nuts selected
*Drill w/ 1/2" high speed bit

I started with 4' of 1/8" x 1&1/2" x 1&1/2" structural aluminum angle like this:

I got it at the local Home Depot for under $20. You can find it online for less, I wanted it quick. You could even use rectangular tube if you wanted which would be stiffer;

Either way, it's cheap and pretty stiff.

I layed the seats flat and pulled back the carpeting in the trunk directly behind the seats, exposing the strut tops and c-pillars directly behind the seats. I found the 2 pair of 1/2" holes in the c-pillars on each side. Next to the outside hole, there is a pinch-weld, or at least another layer of metal - you need to measure the distance between these welds - this is the max length of the bar. I don't remember the length - I'll update soon with this measurement.

Cut the bar to length. I used and angle grinder with cutting wheel. You could use a hack saw or even a dremel but it would take a while. You defiantly want to clamp it down while cutting and wear some sort of safety goggles 'cause the metal will fly. It doesn't have to be pretty - the carpet will cover the ends.

Test fit the bar to make sure is fits flat against the c-pillars. Using a level (assuming the car is on level ground - you could just eyeball it, or measure to center the holes on the bar,) and mark the 4 holes.

Remove the bar and drill your holes with a high-speed bit. Replace it in the car and bolt it up. You'll need to use the socket on the trunk side and a flat wrench on the seat side due to clearance on the outside bolt.

Next, was the hardest part - cutting the carpet to cleanly fit around the bar. Looking back, I recommend doing this before installing the brace. Visualize how the brace will fit against the c-pillar were the four holes are. Mark the holes on the carpet, and cut a corresponding L-shape and a straight line forward toward the seats all the way to the edge of the carpet. Pull it back, install the bar and muscle the carpet back into place.

What I did; installed the bar, and tried to visualize where the carpet fit back. Crudely measured and cut once, twice three times on the left side. Muscled the carpet back into place, then did a much cleaner job on the right side.

UPDATE;
Ok, after delaying for 2 weeks (sorry, my kids take up most of my free time) here are some pics. Not the greatest, but you get a good look of the finished product.

Here it is from the trunk looking in;


Here is another from the passenger side back seat with the seat folded;


And here is a close up of the passenger side where it bolts to the chassis - taken from the trunk with the carpeting pulled back;


As you can see in pic 1, I could have done a better job with the carpet. In pic 3, you can see that my first measurement was a bit off, and I had to notch that side to clear a weld. If I cared more I would have cleaned it up a bit but as you can tell the carpet covers that up so no biggie. Overall, I'd say on a scale of 1-10 the difficulty is about a 6, just because you have to cut and drill some metal, but it really just depends on the tools you have. I did the whole thing in about 30 minutes. Let me know if you have questions or want to see other pics, I have solved my issue with the camera so I should be able to respond to pic requests much quicker now.

Like others have said - it's not going to change your car into a track demon, but for ~$20, and ~30-60 minutes, it's well worth the noticeable reduction in oversteer.

Cheers

[razasasin]

I haven't gotten a chance to really flog it, but the rear end does feel a bit more buttoned-down. Incrementally less under steer, and body roll - enough to notice. I think once I get some better tires on it will be more pronounced. Next mod is a front STB. If past experience is anything, the combo will aid greatly in getting the car to rotate on command.

[bueno4x4]

interesting...subscribed for pics



Bueno

[King Bob]

i did the same thing with some shackles some chain and a turnbuckle so I can adjust the trension

[sdblurjdmsquad]

in for pics please post

[chezfrenchnamese]

Pictures please!

[IceMurder]

more pics

[King Bob]

here are pics of mine. I still need to trim the extra chain.

yeah its ghetto but that's the diy spirit. I like my design because I can adjust the tension by turning the turnbuckle.

[8thgenInAL]

How does a chain work bob, I mean whats your thought process behind it. I thought the idea of the bar was to stiffen up that area. I chain can't really be compressed and hold its shape like the bar can.

[chrisfrofro]

Originally Posted by 8thgenInAL

How does a chain work bob, I mean whats your thought process behind it. I thought the idea of the bar was to stiffen up that area. I chain can't really be compressed and hold its shape like the bar can.

Yea I looked at it and thought the same thing.

[GreyK20]

subscribed really wanna do this

[King Bob]

well the way I figure it the bar resists compression but only after a small amount of travel (until any slack is made up for by the car flexing) and the same on expansion. What I am saying is that the car must flex slightly before the bar will begin to resist. My "design" (lol) only resist expansion ( which honestly I don't know how much there is when cornering) but due to the preloaded tension on the chain it resists any and all expansion at all times. This was a brain fart and I had the materials already in my garage so I decided to try it. I am not much of one to think small mods make much of a difference but I can honestly say I think this has somehow increased my car's tendency to over steer, which I like. It could be psychological or it could be the fact that the chain is seriously tight, like vibrates when you strum it tight. Maybe some one more familiar with suspension geometry/theory would like to chime in, I am always willing to learn something new even if I am just proven wrong, lol.

[razasasin]

The chain is similar to the setup I had on my old nx2000 - I did an aluminum bar (it mounted on the rear strut tops,) but it was seriously flimsy. So, it kept the struts from flexing out, but not in. It did make a major difference in getting the car to rotate (oversteer), but that was in conjunction with a front stb and the battery relocated to the rear.

I used a much stiffer bar on the si, and it's bolted in tight; - there is no slack as Bob mentioned above - it stiffens all around. I think the chain isn't a terrible idea if it's all you have, but inferior to a bar. A stiff bar helps keep struts from flexing together, as in a hard right turn would put outward stress to the left = both sides go to the left a bit. The chain doesn't prevent this as there is only one mount point. The bar mounts to two holes on each side, 4 points total, create more stiffness in all situations.

I know I created this thread and haven't posted actual pics yet. I'm planning on getting them up tonight - thanks for your patience...

[razasasin]

Ok I went out and took the pix, but now I can't find my mini usb for the camera, and my sd card is bad... hmmm it might be another day or two. My apologies.

[Solo2EG]

Originally Posted by razasasin

I used a much stiffer bar on the si, and it's bolted in tight; - there is no slack as Bob mentioned above - it stiffens all around. I think the chain isn't a terrible idea if it's all you have, but inferior to a bar. A stiff bar helps keep struts from flexing together, as in a hard right turn would put outward stress to the left = both sides go to the left a bit. The chain doesn't prevent this as there is only one mount point. The bar mounts to two holes on each side, 4 points total, create more stiffness in all situations.

I know I created this thread and haven't posted actual pics yet. I'm planning on getting them up tonight - thanks for your patience...

The thing is that there is no rear strut assembly on the 8th gen Civic, with a separate spring and damper (with the spring under the floor) there is really no benefit in tying the tops of the damper towers together. And even so, I'm not sure where your bar is but I know the store bought ones don't even really do that, thay just sit behind the seat, you could call it chassis bracing (I guess) but it does ZERO for the suspension...

[razasasin]

Originally Posted by Solo2EG

The thing is that there is no rear strut assembly on the 8th gen Civic, with a separate spring and damper (with the spring under the floor) there is really no benefit in tying the tops of the damper towers together. And even so, I'm not sure where your bar is but I know the store bought ones don't even really do that, thay just sit behind the seat, you could call it chassis bracing (I guess) but it does ZERO for the suspension...

Well, there are rear struts, they're just not in a spot that you can add a brace easily, but the bracing point that I (and the braces available for purchase) use is connected to them. As for it doing 'zero' for the suspension, there is a noticeable reduction in understeer so there is some benefit. I didn't claim to develop the idea on a chassis dyno, I just saw braces for sale and said, 'i can make that,' and it was cheap enough that there was no harm in trying. Now that it's done, I can 'feel' a difference when taking high speed corners like freeway interchange, entrance/exit. Can't say for sure that it is a measurable difference, but pretty sure that it's identical to what would happen for you if you bought a trunk brace and installed it...

[Solo2EG]

Originally Posted by razasasin

Well, there are rear struts, they're just not in a spot that you can add a brace easily, but the bracing point that I (and the braces available for purchase) use is connected to them. As for it doing 'zero' for the suspension, there is a noticeable reduction in understeer so there is some benefit. I didn't claim to develop the idea on a chassis dyno, I just saw braces for sale and said, 'i can make that,' and it was cheap enough that there was no harm in trying. Now that it's done, I can 'feel' a difference when taking high speed corners like freeway interchange, entrance/exit. Can't say for sure that it is a measurable difference, but pretty sure that it's identical to what would happen for you if you bought a trunk brace and installed it...

You are right, it is the same as adding the trunk brace, I'm sure you did good work!

But FYI, a strut is defined as a damper & spring assembly together, the rear of an 8th Civic does not have this, these 2 components are separated and the damper is alone (while the spring sits under the floor) so there is not nearly the same load on the damper as there is on a "strut" in most cars (because the load is on the springs) so tying the damper towers together is not really beneficial.

[razasasin]

Originally Posted by Solo2EG

You are right, it is the same as adding the trunk brace, I'm sure you did good work!

But FYI, a strut is defined as a damper & spring assembly together, the rear of an 8th Civic does not have this, these 2 components are separated and the damper is alone (while the spring sits under the floor) so there is not nearly the same load on the damper as there is on a "strut" in most cars (because the load is on the springs) so tying the damper towers together is not really beneficial.

I agree...

[CorSport]

Originally Posted by chrisfrofro

Yea I looked at it and thought the same thing.

Bingo.

[BLouIsGod]

That chain set-up belongs on a 1985 Escort, not a 2006+ Si, imo.