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Discussion Starter · #1 ·
So I was on my way to Michigan for the first trackday of the year, and once I hit about 75-80 on the highway, I hear a bang from underneath the car. I pull over and see the undertray hanging loose. It looks like a bunch of the fasteners came loose and after the banging around, many of them are gone. I cannot reattach the undertray as-is, so I'm asking:

1) can I easily reattach the undertray with something from the hardware store? I bought my car used and it has these quarter turn fasteners that screw into some kind of clip. I've never seen these at a hardware store, but maybe I just need to ask? I don't think this is the stock fastener.

2) can I run without it? This would be about 3 hours each way on the highway and then 2 days of track time. I'm thinking this is a no, but I guess I should ask.
 

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The quarter-turn studs were probably not fully "clicked" into place. I have a set on my tray and diffuser and have never had even one come loose.

The OEM method of fastening the tray is with small cap screws which thread into body-panel clips. I know I have seen the standard clips at a hardware store in the past. Maybe you can find some in time. You'll also need a cap screw and washer for each clip.

Do you know any forum members in the Chicago area? Maybe someone has some spare clips they could loan you...
 

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No...go to Home Depot and buy some of that aluminum A/C ducting tape...it is in the plumbing department. Tape it all together for the track day... It is not the standard ducktape that I'm talking about. It is actually made out of aluminum foil. You peal off the brown backing and tape it together... Im the aerospace industry, we call that speed tape. Have fun on the track.
 

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Should be able to find decent bolts and washers to do the job, and the two bigger bolts at a hardware, but a proper nut and bolt place could probs get stainless.

Really makes one wonder how this can happen, how so many can loosen and disappear. But it happened to me, turn one road atlanta. Maybe evil trolls?

And I just don't see the quarter turn deals as needed. A small electric screwdriver with a nut driver can take em on or off in maybe 4 seconds.
 

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You need six 8MM screws. 3 on the left and 3 on the right + washers for each screw. then you need clips that slide on to the side panel body.

If you need to attach the diffuser to the under tray, add another 5 screws/washers/clips. Hopefully somebody has some in the CHI area. There are 2 big screws as well, which are 13 MM
 

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You need six 8MM screws. 3 on the left and 3 on the right + washers for each screw. then you need clips that slide on to the side panel body.

If you need to attach the diffuser to the under tray, add another 5 screws/washers/clips. Hopefully somebody has some in the CHI area. There are 2 big screws as well, which are 13 MM
NO!!!! Those are M5 screws with an 8mm head. You have to buy 5mm screws and not 8 as this guy says. An M8 screw has a 13mm wrench.
 

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:popcorn:
 

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Discussion Starter · #13 ·
Thanks for all the help on short notice. I ended up redistributing the remaining fasteners and I was able to make the 3hr trip without incident. I bought a roll of metal "speed tape" just in case. I'll keep an eye on it and figure out a more permenant solution later.
 

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Essentially, any 10-32 fastener will do for the outer screws.
The big bolts are 8 mm. Use washers on them.
Sam
 

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Thanks for all the help on short notice. I ended up redistributing the remaining fasteners and I was able to make the 3hr trip without incident. I bought a roll of metal "speed tape" just in case. I'll keep an eye on it and figure out a more permenant solution later.
Were the original 1/4-turn fasteners loose? Is that why they fell out? Covering those fasteners with speed tape does two things...it works like safety wire and prevents them from coming loose/out and it aerodynamically fairs the heads... Taping the seams also aerodynamically fairs the joints. You will go faster with them taped...that is why its called speed tape. :up:

I've made aluminum blanking plates for the exhaust tip hole in the diffuser and for the NACA duct openings. The only thing holding them in is speed tape...they have been in that way for over a year now, so that speed tape is great stuff!
 

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No...go to Home Depot and buy some of that aluminum A/C ducting tape...it is in the plumbing department. Tape it all together for the track day... It is not the standard ducktape that I'm talking about. It is actually made out of aluminum foil. You peal off the brown backing and tape it together... Im the aerospace industry, we call that speed tape. Have fun on the track.
This tape is excellent. Good idea.
 

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Don't run without the undertray

The tray under the engine bay is structural and you should not run without it. Although the edges are secured with small bolts and probably don't do much, the two large interior bolts anchor the tray to the chassis and create a torsion box. Without the tray properly attached, the frame will flex more, which will affect handling and stress your frame.
 

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The tray under the engine bay is structural and you should not run without it. Although the edges are secured with small bolts and probably don't do much, the two large interior bolts anchor the tray to the chassis and create a torsion box. Without the tray properly attached, the frame will flex more, which will affect handling and stress your frame.
No it's not! The shear panel above that under-tray (under the fuel tank) is structural. A shear panel does absolutely nothing for torsional rigidity. And the rest is just pure BS... :facepalm

Now...if you had on continuous under-tray/diffuser made from a honeycomb sandwich construction of carbon fiber and securely fastened the four M8 screws, then you would have a shear panel for added rigidity, but still nothing for torsional rigidity... but as it is right now, it is only an aerodynamic fairing.
 

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The tray under the engine bay is structural and you should not run without it. Although the edges are secured with small bolts and probably don't do much, the two large interior bolts anchor the tray to the chassis and create a torsion box. Without the tray properly attached, the frame will flex more, which will affect handling and stress your frame.
The undertray is nowhere near structural.

The PO of my car ran without it intentionally, to make oil changes easier.

Aside from a dirtier engine than normal, there was no difference in how the car handled/drove (I do run it for legality reasons).

The two big bolts are the only ones that'd do _ANYTHING_ for rigidity, the little woodscrews on the sides do nothing, the ones connecting it to the rear diffuser do nothing - beyond hold it on the car. Heck, it is not even CONNECTED to the car at the front, just sits on a shelf.

I run mine, will continue to do so, but a track day without it is not going to hurt a thing.

.02c



Iain
 

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What bothers me is that the bolts we're loose enough to fall out! What else is ready to fail???? Prior to any track day all suspension, brake, lug nuts, and rear toe links must be checked for proper torque! You took a huge gamble, but glad you made it out ok! Next time please do a full inspection on the car. Your life and the other drivers safety depends on it.
 
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