DIY: Front Tow Hook

[SonicWRX]

Originally Posted by 02wrxRally

and if your used 02 wrx didn't have that bag in the trunk? I looked on subarugenuineparts and found a part called "tow hook", but the diagram shows it's the rear. There's another part called "hook", but there's no diagram for it. Is that it? Is there a reason the stock one won't work for track days? If not, I'm just going to paint them red and call it done (once I hunt down a front, that is).

No clue on the stock front hook part number. Search around it should turn up in either the forums or a parts catalog. It might even be listed under "tool kit" if they don't sell it separately. My kit had a lug wrench, the tow hook, a screwdriver and something else I can't recall.

I think you should still be OK with the stocker. The reason these bigger hooks are popular is that most tracks will come get you with a tow strap and those won't fit through the stock hook. They would have to have a hook or clip of some sort on their strap to hook in.

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[Admission_Regret]

I probably would have used a Button head cap screw in stainless, not bad though, good idea!

[SonicWRX]

Originally Posted by Admission_Regret

I probably would have used a Button head cap screw in stainless, not bad though, good idea!

Agreed on the button head. I went with what I could find and even that took 3 stores.

Stainless will give up a lot of strength, but won't corrode like this SHCS will. It's got a black oxide on it, but it will eventually lose to the elements.

[Admission_Regret]

True, but do you think your forces are really going to be that high, I would imagine the shackle would fail first.

http://www.mcmaster.com/#92949a769/=2cvqqv

http://www.mcmaster.com/#92488a352/=2cvs3d

Anti corrosion comes at a price.
The oxide should hold up for a while and at that price, you could swap it out at least 10 times.

[domestic_abuser]

Originally Posted by BenGSX

No offense..

what?

[SonicWRX]

Originally Posted by Admission_Regret

True, but do you think your forces are really going to be that high, I would imagine the shackle would fail first.

Working on that answer. I've got the assembly in SolidWorks Simulation and am getting ready to load it and break it.

Anti corrosion comes at a price. The oxide should hold up for a while and at that price, you could swap it out at least 10 times.

So true. The SS is always so high. You can get it with a special black coating also, but that is even more ridiculous.

[SubieWReX]

Awesome mod. If I had a car that I could actually use it on and not be posing I would definitely go this route. Tow hooks would be just meh for my practically stock-looking stage 2.

[bcWRX-02]

Originally Posted by 02wrxRally

and if your used 02 wrx didn't have that bag in the trunk? I looked on subarugenuineparts and found a part called "tow hook", but the diagram shows it's the rear. There's another part called "hook", but there's no diagram for it. Is that it? Is there a reason the stock one won't work for track days? If not, I'm just going to paint them red and call it done (once I hunt down a front, that is).

I could be wrong here, but I think most track regs require a 2" inner diameter tow hook. Although whether this applies to the weekend warriors and occasional track goers I'm not sure. If that is the case, the stock one obviously doesn't cut it, and neither would this DIY one.

[williaty]

I am interested in your results with the FEA. I'd like to do this, but I am WAY too familiar with how quickly that black gunk comes off and lets the metal start rusting. Stainless for me.

[FunkRider]

Originally Posted by SonicWRX

Shear strength of the SHCS is just over 31,000 lbs

Tensile strength of the shackle is rated at 4,000 lbs

I would guess looking at the cross section of the stock tow hook that it would be in 15,000 lbs tensile range.

I will see if I can get the assembly into SolidWorks and break it with an FEA analysis to give a better answer.

I would assume that shear strength rating is double shear and not single? Not that it matters I'm just curious. lol

[dtfdanyo]

looks easy to jack

[SonicWRX]

Originally Posted by williaty

I am interested in your results with the FEA. I'd like to do this, but I am WAY too familiar with how quickly that black gunk comes off and lets the metal start rusting. Stainless for me.

Got all the loads, constraints, fixtures, etc and ran the numbers. With a 10,000 lb pull on the shackle, the stock tow hook gets close to its 30,000 psi yield in the area just above the threads and before the first chamfer. It was by far the most compromised part of the assembly. We were still playing with it when I ran out of time so I'll get some screen caps tomorrow.

Yes, I am trying to find a SS button head but nothing yet and Fastenal doesn't like to sell oneseys.

I would assume that shear strength rating is double shear and not single?

That was the number reported on the manufacturer's website. I pretty much ignored it in SolidWorks by going through and defining actual materials for the individual components.

I could be wrong here, but I think most track regs require a 2" inner diameter tow hook.

You could be right. This one would not make the grade and I doubt if this approach would work due to clearance issues I mentioned above.

[JavaBot]

Does it wobble when you're driving? Is it tightly torqued? Otherwise it will F up your bumper, looks good but I'm not a huge fan of the droopyness.

[SonicWRX]

Originally Posted by msesno

Does it wobble when you're driving? Is it tightly torqued? Otherwise it will F up your bumper, looks good but I'm not a huge fan of the droopyness.

Not at all. Replacing the shackle pin with a SHCS allows you to tighten the shackle so it won't move unless forced and the split washer keeps the SHCS from backing out.

[SonicWRX]

Ground off the cast-in text, repainted the shackle, painted the stock hook black and got this: (still need that button head!)




Here is the graphical output from an FEA in SolidWorks Simulation Pro. I constrained the stock hook at its threaded section then loaded the assembly with a 20,000 pound pull using a big ring (since I don't know how to draw a tow strap). The yield strength of alloy steel is around 90,000 psi (not 30,000 like I said above) and you can see from the colored von Mises scale that anything red is bad.

There are two stress risers in the stock hook: one just up from the threads and one not as bad near the first chamfer. You can also see some high compressive stresses where the ring meets the shackle, but with a tow strap those will go away.

CN: Stock hook will break before the stuff I added.

[bigolrig]

^^ thats pretty neat

[98Legacy_757]

wow thats pretty legit

[williaty]

Originally Posted by SonicWRX

CN: Stock hook will break before the stuff I added.

CN: stock tow hook will break first at the most annoyingly difficult to remove place possible.

[SonicWRX]

Originally Posted by williaty

CN: stock tow hook will break first at the most annoyingly difficult to remove place possible.

For sure. That's a written rule right close to "Fasteners dropped while working in the engine compartment will either go down the intake or not make it to the floor if they somehow miss the intake."

[bcWRX-02]

Epic Solidworks sim. Well done sir. You must have some sort of engineering background because I've played with that program before (without an engineering background) and it took me literally a couple hours to design a bolt

I just picked up all the stuff to do this. Originally I was gonna design something similar to the nukabe and have a friend cut it out with a waterjet, but I almost like this look better, and I really only need it there for the winter, whereas the nukabe would be on there all the time.

[SonicWRX]

Originally Posted by bcWRX-02

Epic Solidworks sim. Well done sir. You must have some sort of engineering background because I've played with that program before (without an engineering background) and it took me literally a couple hours to design a bolt

I just picked up all the stuff to do this. Originally I was gonna design something similar to the nukabe and have a friend cut it out with a waterjet, but I almost like this look better, and I really only need it there for the winter, whereas the nukabe would be on there all the time.

Thanks. And yes, 22 years of mechanical engineering behind me so far. I'm not a SolidWorks jock by any stretch, but I have some guys working for me who can really kill it. When I get stuck, they help me out.

[jcbluescooby]

solidworks FTW..lol..mechanical engineering student myself and am actually doing an intern right now where i make car suspension parts (mostly suspension mounts and end links) in soldiworks and then send out the drawings to get made..this is an awesome mod..will be heading to home depot when i get out of work

[SonicWRX]

Originally Posted by jcbluescooby

solidworks FTW..lol..mechanical engineering student myself and am actually doing an intern right now where i make car suspension parts (mostly suspension mounts and end links) in soldiworks and then send out the drawings to get made

Sweet! The guys at TiC did the same thing for their new "drag racing ALK". Part was designed in SW then laid down by a 3D printer for test fitting/prototyping.

I NEED a 3D printer!

[recce02]

If I can throw out a suggestion. First, I like the tow hook looks great. Second, you can add a piece of clear vinyl under the D ring to prevent it from scratching the paint on the bumper.

[jcbluescooby]

its on their tight i believe so that the wind wont be able to push it back against the bumper